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{{Short description|Motor vehicle manual gearbox; stick shift}}
{{pp-semi-vandalism}}
{{Redirect|Stick Shift|the video game|Stick Shift (video game)}}
{{transmission types}}
[[File:M5OD transmission.jpg|thumb|right|[[Mazda M5OD transmission|Mazda M5OD]] manual transmission for a four-wheel-drive vehicle ([[Ford Ranger]]) viewed from the engine side]]
A '''manual transmission''' (also known as a '''stick shift''' or just '''stick''', '''straight drive''', or '''standard transmission''') is a type of [[Transmission (mechanics)|transmission]] used in [[automotive]] applications. Manual transmissions often feature a [[driving|driver]]-operated [[clutch]] and a movable [[gear]] selector. Most automobile manual transmissions allow the driver to select any gear at any time, but some, such as those commonly mounted on [[motorcycle]]s and some types of racing cars, only allow the driver to select the next-highest or next-lowest [[gear ratio]]. This second type of transmission is sometimes called a '''[[sequential manual transmission]]'''.
[[File:Getrag282internals.jpg|thumb|Internals of a [[Getrag 282 transmission|Getrag 282]] manual transmission for a front-wheel-drive vehicle ([[Oldsmobile Cutlass]])]]
 
A '''manual transmission''' ('''MT'''), also known as '''manual gearbox''', '''standard transmission''' (in [[Canadian English|Canada]], [[British English|the United Kingdom]] and [[American English|the United States]]), or '''stick shift''' (in the United States), is a multi-speed [[motor vehicle]] [[Transmission (mechanical device)|transmission system]] where gear changes require the driver to manually select the gears by operating a [[gear stick]] and [[clutch]] (which is usually a foot pedal for cars or a hand lever for motorcycles).
Manual transmissions are characterized by gear ratios that are selectable by engaging pairs of gears inside the transmission. Conversely, most [[automatic transmission]]s feature [[epicyclic gearing|epicyclic]] ([[epicyclic gearing|planetary]]) gearing controlled by brake bands and/or clutch packs to select gear ratio. [[Automatic transmission]]s that allow the driver to manually select the current gear are called [[semi-automatic transmission]]s.
 
ContemporaryEarly automotiveautomobiles used ''sliding-mesh'' manual transmissions are generally available with fourup to sixthree forward gearsgear andratios. oneSince reversethe gear1950s, although''constant-mesh'' manual transmissions have beenbecome builtincreasingly with as few as twocommonplace, and as many as eight gears. [[Semi-trucks]] have at least 13 gears and as many as 24. Some manuals are referred to by the number of forward gearsratios theyhas offerincreased (e.g.,to '''5-speed''') asand a way of distinguishing between automatic or other available6-speed manual transmissions. Similarly,for acurrent 5-speed automatic transmission is referred to as a ''5-speed automatic''vehicles.
 
OtherThe typesalternative ofto transmissiona inmanual mainstreamtransmission automotiveis use are thean [[automatic transmission]],. Common types of automatic transmissions are the [[semi-Automatic transmission#Hydraulic automatic transmissions|hydraulic automatic transmission]], (AT) and the [[continuously variable transmission]] (CVT). The [[automated manual transmission]] (AMT) and [[dual-clutch transmission]] (DCT) are internally similar to a conventional manual transmission, but are shifted automatically.
 
Alternatively, there are [[semi-automatic transmission|semi-automatic transmissions]]. These systems are based on the design of, and are technically similar to, a conventional manual transmission. They have a gear shifter which requires the driver's input to manually change gears, but the driver is not required to engage a clutch pedal before changing gear. Instead, the mechanical linkage for the clutch pedal is replaced by an [[actuator]], [[servomechanism|servo]], or [[Solenoid valve|solenoid]] and [[sensor]]s, which operate the clutch system automatically when the driver touches or moves the [[gearshift]]. This removes the need for a physical clutch pedal.
Manual transmissions come in two basic types: simple non-synchronous systems, where gears are spinning freely and their relative speeds must be synchronized by the operator to avoid noisy and damaging "clashing" and "grinding" when trying to mesh the rotating teeth; and synchronized systems, which eliminate this necessity while changing gears.
 
==Overview==
==Unsynchronized transmission==
A manual transmission requires the driver to operate the [[gear stick]] and [[clutch]] in order to change gears (unlike an [[automatic transmission]] or [[semi-automatic transmission]], where one (typically the clutch) or both of these functions are [[Automation|automated]]). Most manual transmissions for cars allow the driver to select any gear ratio at any time, for example shifting from second to fourth gear, or fifth to third gear. However, [[sequential manual transmission]]s, which are commonly used in [[motorcycle]]s and [[racing car]]s, only allow the driver to select the next-higher or next-lower gear.
The earliest vehicle transmissions could be shifted, with multiple gear ratios available to the operator, and even had reverse. However, the gears were engaged by sliding mechanisms or simple clutches, which required a lot of careful timing and [[throttle]] manipulation when shifting, so that the gears would be spinning at roughly the same speed when engaged; otherwise, the teeth would refuse to mesh.
 
In a vehicle with a manual transmission, the [[flywheel]] is attached to the engine's [[crankshaft]], therefore rotating at engine speed. A clutch disc sits between the flywheel and the transmission pressure plate which is attached to the transmission input shaft, controlling whether the transmission is connected to the engine or not. The clutch pedal controls the pressure plate (''clutch engaged'' – the clutch pedal is not being pressed) or not connected to the engine (''clutch disengaged'' – the clutch pedal is being pressed down). When the engine is running and the clutch is engaged (i.e., clutch pedal up), the flywheel spins the clutch pressure plate and hence the transmission.
When upshifting, the speed of the gear driven by the engine had to drop to match the speed of the next gear; as this happened naturally when the [[clutch]] was depressed or disengaged, it was just a matter of skill and experience to hear and feel when the gears managed to mesh. However, when downshifting, the gear driven by the engine had to be sped up to mesh with the output gear, requiring letting the clutch up (engagement) for the engine to speed up the gears. [[Double declutch]]ing, that is, shifting once to neutral to speed up the gears and again to the lower gear, is sometimes needed. In fact, such transmissions are often easier to shift without using the clutch at all. When using this method, the driver has to time the shift with relative precision to avoid grinding the gears. The clutch, in these cases, is only used for starting from a standstill. This procedure is common in racing vehicles and most production motorcycles.
 
The design of most manual transmissions for cars is that gear ratios are selected by locking selected gear pairs to the output shaft inside the transmission. This is a fundamental difference compared with a typical [[Automatic transmission#Hydraulic automatic transmissions|hydraulic automatic transmission]], which uses an [[epicyclic gearing|epicyclic]] (planetary) design, and a [[torque converter|hydraulic torque converter]]. An automatic transmission that allows the driver to control the gear selection (such as shift paddles or "+/−" positions on the gear selector) is called a [[manumatic]] transmission, and is not considered a manual transmission. Some automatic transmissions are based on the mechanical build and internal design of a manual transmission but have added components (such as [[computer]]-controlled [[actuator]]s and [[sensor]]s) which automatically control the timing and speed of the gear shifts and clutch; this design is typically called an [[automated manual transmission]] (or sometimes a ''clutchless manual transmission'').
Even though automotive transmissions are now almost universally synchronised, heavy [[truck]]s and machinery as well as dedicated [[automobile racing|racing]] transmissions are usually non-synchromesh transmissions, known colloquially as "crashboxes", for several reasons. The friction material, such as brass, in synchronizers is more prone to wear and breakage than gears, which are forged steel, and the simplicity of the mechanism improves reliability and reduces cost. In addition, the process of shifting a synchromesh transmission is slower than that of shifting a non-synchromesh transmission. For racing of production-based transmissions, sometimes half the teeth (or "dogs") on the synchros are removed to speed the shifting process, at the expense of greater wear.
 
Contemporary manual transmissions for cars typically use five or six forward gears ratios and one reverse gear; however, transmissions with between two and seven gears have been produced at times. Transmissions for trucks and other heavy equipment often have between eight and twenty-five gears, in order to keep the engine speed within the optimal [[power band]] for all typical road speeds. Operating such transmissions often uses the same pattern of shifter movement with a single or multiple switches to engage the next sequence of gears.
Heavy duty trucks utilize unsynchronized transmissions in the interest of saving weight. Military edition trucks, which do not have to obey weight laws, usually have a synchronized transmission. Highway use heavy-duty trucks in the United States are limited to 80,000 pounds GVWR, and the lighter the curb weight for the truck, the more cargo can be carried, and with a synchronizer adding weight to a truck that could otherwise be used to carry cargo, most drivers are simply taught how to double clutch.
 
<gallery class="center" heights="160px" widths="220px" caption="Manual transmissions in operation">
Similarly, most modern motorcycles still utilize unsynchronized transmissions as synchronizers are generally not necessary or desirable. Their low gear inertias and higher strengths mean that 'forcing' the gears to alter speed is not damaging, and the selector method on modern motorcycles (pedal operated) is not conducive to having the long [[shift time]] of a synchronized gearbox. Because of this, it is still necessary to synchronize gear speeds by "blipping" the throttle when shifting into a lower gear on a motorcycle.
File:Gearbox 4gears.gif|Operation of a constant-mesh 4-speed manual transmission
File:Crash gearbox 3gears and reverse.gif|Non-synchronous "crash" gearbox; with ''sliding-mesh'' design, used in older vehicles
File:Gearbox 4gears sequential.gif|Operation of a constant-mesh 4-speed sequential manual transmission, commonly used in [[motorcycles]] and [[race car]]s
File:0762 Spinning Levers 04 45 20 00 3mb.webm|1936 film of automobile gearbox
</gallery>
 
== History ==
==Synchronized transmission==
=== 1890s to 1940s ===
[[Image:Ford Design 3-speed OD Transmission w. Hurst Shifter.jpg|thumb|right|400px|Top and side view of a typical manual transmission, in this case a Ford [[Toploader Transmission|"Toploader"]], used in cars with external floor shifters.]]
[[File: PSM V57 D608 Cherrier two speed gear.png|thumb|right|Cherrier two speed gear, {{Circa|1900}}<ref>[[Wikisource:Popular Science Monthly/Volume 57/August 1900/The Evolution and Present Status of the Automobile]]</ref>]]
Modern gearboxes are '''constant mesh''', i.e. all gears are always in mesh. Only one of these meshed pairs of gears is locked to the shaft on which it is mounted at any one time, while the others are allowed to rotate freely. Thus, it greatly reduces the skill required to shift gears.
 
Many of the first automobiles were rear-engined, with a simple belt-drive functioning as a single-speed transmission. The 1891 [[Panhard#Early years|Panhard et Levassor]] is considered a significant advance in automotive transmissions since it used a three-speed manual transmission.<ref>{{cite web |title=The 1891 Panhard et Levassor |url=https://www.themotormuseuminminiature.co.uk/1891-panhard.php |website=www.themotormuseuminminiature.co.uk |access-date=2 July 2020}}</ref><ref>{{cite web |title=Sliding Gearbox - 1891 Panhard et Levassor |url=https://www.youtube.com/watch?v=VkrjueYVvYA | archive-url=https://ghostarchive.org/varchive/youtube/20211030/VkrjueYVvYA| archive-date=2021-10-30|website=www.youtube.com |access-date=2 July 2020}}{{cbignore}}</ref> This transmission, along with many similar designs that it inspired, was a [[non-synchronous transmission|non-synchronous]] (also called ''sliding-mesh'') design where gear changes involved sliding the gears along their shafts so that the desired cogs became meshed. The driver was therefore required to use careful timing and [[throttle]] manipulation when shifting, so the gears would be spinning at roughly the same speed when engaged; otherwise, the teeth would refuse to mesh. This was difficult to achieve, so gear changes were often accompanied by grinding or crunching sounds, resulting in the gearboxes being nicknamed "crash boxes".<ref>{{cite web |title=1902 Panhard and Levassor |url=https://auto.howstuffworks.com/1902-panhard-and-levassor1.htm |website=www.howstuffworks.com |access-date=2 July 2020 |language=en |date=7 December 2007 |archive-date=4 July 2020 |archive-url=https://web.archive.org/web/20200704154635/https://auto.howstuffworks.com/1902-panhard-and-levassor1.htm |url-status=dead }}</ref> Even after passenger cars had switched to synchronous transmissions (i.e. with synchronizers), many transmissions for heavy trucks, motorcycles and racing cars remained non-synchronous, in order to withstand the forces required or provide a faster [[shift time]].
Most modern cars are fitted with a synchronized gear box, although it is entirely possible to construct a constant mesh gearbox without a synchromesh, as found in a motorcycle, for example. In a constant mesh gearbox, the transmission gears are always in mesh and rotating, but the gears are not rigidly connected to the shafts on which they rotate. Instead, the gears can freely rotate or be locked to the shaft on which they are carried. The locking mechanism for any individual gear consists of a collar (or "dog collar") on the shaft which is able to slide sideways so that teeth (or "dogs") on its inner surface bridge two circular rings with teeth on their outer circumference: one attached to the gear, one to the shaft (one collar typically serves for two gears; sliding in one direction selects one transmission speed, in the other direction selects the other). When the rings are bridged by the collar, that particular gear is rotationally locked to the shaft and determines the output speed of the transmission. In a synchromesh gearbox, to correctly match the speed of the gear to that of the shaft as the gear is engaged, the collar initially applies a force to a cone-shaped brass clutch which is attached to the gear, which brings the speeds to match prior to the collar locking into place. The collar is prevented from bridging the locking rings when the speeds are mismatched by synchro rings (also called blocker rings or balk rings, the latter being spelled "baulk" in the UK). The gearshift lever manipulates the collars using a set of [[linkage]]s, so arranged so that one collar may be permitted to lock only one gear at any one time; when "shifting gears," the locking collar from one gear is disengaged and that of another engaged. In a modern gearbox, the action of all of these components is so smooth and fast it is hardly noticed.
 
=== 1950s to 1980s ===
The modern cone system was developed by [[Porsche]] and introduced in the [[1952]] [[Porsche 356]]; cone synchronizers were called "Porsche-type" for many years after this. In the early [[1950s]] only the second-third shift was synchromesh in most cars, requiring only a single synchro and a simple linkage; drivers' manuals in cars suggested that if the driver needed to shift from second to first, it was best to come to a complete stop then shift into first and start up again. With continuing sophistication of mechanical development, however, fully synchromesh transmissions with three speeds, then four speeds, five speeds, six speeds and so on became universal by the [[1960s]]. Reverse gear, however, is usually not synchromesh, as there is only one reverse gear in the normal automotive transmission and changing gears in reverse is not required. (The obvious exception to this is in cars made by [[Lamborghini]], almost all of whose models have synchromesh on reverse gear - presumably because the designers were thinking of drivers engaging reverse while still moving forward.)
[[File: Ford Design 3-speed OD Transmission w. Hurst Shifter.jpg|thumb|right|Top and side view of a typical manual transmission, in this case, a Ford [[Ford Toploader transmission|Toploader]], used in vehicles with external floor shifters]]
 
The first car to use a manual transmission with [[#Synchromesh|synchromesh]] was the [[List of Cadillac vehicles#1920s|1929 Cadillac]].<ref name="hemmings synchromesh">{{cite web |title=Synchromesh Gearbox |url=https://www.hemmings.com/stories/article/synchromesh-gearbox |website=www.hemmings.com |access-date=5 July 2020}}</ref> Most North American marques had adopted synchronized manual transmissions, usually for second and high gears, by the mid-1930s. In 1947, Porsche patented the ''split ring'' synchromesh system.<ref>{{cite web |title=Synchromesh - How It Works |url=https://www.uniquecarsandparts.com.au/how_it_works_synchromesh |website=www.uniquecarsandparts.com.au |access-date=5 July 2020}}</ref> The 1952 [[Porsche 356#356 "pre-A"|Porsche 356]] was the first car to use a transmission with synchromesh on all forward gears.<ref>{{cite web |title=Model Guide: 356 — The Simple Porsche |url=https://www.pca.org/news/2017-06-27/model-guide-356-simple-porsche |website=www.pca.org |access-date=5 July 2020}}</ref><ref>{{cite web |title=History of the 356 |url=http://356.dk/html/history/history.html |website=www.356.dk |access-date=5 July 2020 |archive-date=19 August 2015 |archive-url=https://web.archive.org/web/20150819065338/http://356.dk/html/history/history.html |url-status=dead }}</ref> In the early 1950s, most cars only had synchromesh for the shift from third gear to second gear (drivers' manuals in vehicles suggested that if the driver needed to shift from second to first, it was best to come to a complete stop beforehand).
==Internals==
===Shafts===
Like other transmissions, a manual transmission has several shafts with various gears and other components attached to them. Typically, a rear-wheel-drive transmission has three shafts: an input shaft, a ''countershaft'' and an output shaft. The countershaft is sometimes called a ''layshaft''.
 
Up until the late 1970s, most transmissions had three or four forward gear ratios, although five-speed manual transmissions were occasionally used in sports cars such as the 1948 [[Ferrari 166 Inter]] and the 1953 [[Alfa Romeo 1900#1900 Berlina and Sprint|Alfa Romeo 1900 Super Sprint]]. Five-speed transmissions became widespread during the 1980s, as did the use of synchromesh on all forward gears.
In a rear-wheel-drive transmission, the input and output shaft lie along the same line, and may in fact be combined into a single shaft within the transmission. This single shaft is called a ''mainshaft''. The input and output ends of this combined shaft rotate independently, at different speeds, which is possible because one piece slides into a hollow bore in the other piece, where it is supported by a bearing. Sometimes the term ''mainshaft'' refers to just the input shaft or just the output shaft, rather than the entire assembly.
 
=== 1990s to present ===
In some transmissions, it's possible for the input and output components of the mainshaft to be locked together to create a 1:1 gear ratio, causing the power flow to bypass the countershaft. The mainshaft then behaves like a single, solid shaft, a situation referred to as ''direct drive''.
Six-speed manual transmissions started to emerge in high-performance vehicles in the early 1990s, such as the 1990 [[BMW 8 Series (E31)|BMW 850i]] and the 1992 [[Ferrari 456]]. The first 6-speed manual transmission was introduced in the 1967 [[Alfa Romeo 33 Stradale]]. The first 7-speed manual transmission was introduced in the 2012 [[Porsche 991|Porsche 911 (991)]].<ref>{{cite web |title=In Your Car, How Many Gears is Too Many? |url=https://www.popularmechanics.com/cars/a7243/gears-galore-how-many-speeds-is-too-many/ |website=www.popularmechanics.com |access-date=5 July 2020 |date=29 September 2011}}</ref>
 
In 2008, 75.2% of vehicles produced in Western Europe were equipped with manual transmission, versus 16.1% with automatic and 8.7% with other.<ref>{{cite web |url=http://www.dctfacts.com/archive/2008/why-dual-clutch-technology-big-business.aspx |title=Why Dual Clutch Technology Will Be Big Business |publisher=Dctfacts.com |access-date=2010-02-07 |archive-date=25 March 2010 |archive-url=https://web.archive.org/web/20100325205741/http://www.dctfacts.com/archive/2008/why-dual-clutch-technology-big-business.aspx |url-status=dead }}</ref>
Even in transmissions that do not feature direct drive, it's an advantage for the input and output to lie along the same line, because this reduces the amount of [[Torsion (mechanics)|torsion]] that the transmission case has to bear.
{{clear right}}
 
==Internals==
Under one possible design, the transmission's input shaft has just one pinion gear, which drives the countershaft. Along the countershaft are mounted gears of various sizes, which rotate when the input shaft rotates. These gears correspond to the forward speeds and reverse. Each of the forward gears on the countershaft is permanently meshed with a corresponding gear on the output shaft. However, these driven gears are not rigidly attached to the output shaft: although the shaft runs through them, they spin independently of it, which is made possible by [[bearings]] in their hubs. Reverse is typically implemented differently, see the section on [[Manual transmission#Reverse|Reverse]].
[[File:ZF-16S181-transmission-hous.jpg|thumb|16-speed (2×4×2) [[ZF Friedrichshafen|ZF]] 16S181 – opened transmission housing ('''''2×4'''''×2)]]
[[File:ZF-16S181-range.jpg|thumb|16S181 — opened [[Epicyclic gearing|planetary]] range housing (2×4'''''×2''''')]]
 
===Shafts===
Most front-wheel-drive transmissions for transverse engine mounting are designed differently. For one thing, they have an integral final drive and differential. For another, they usually have only two shafts; input and countershaft, sometimes called input and output. The input shaft runs the whole length of the gearbox, and there is no separate input pinion. At the end of the second (counter/output) shaft is a pinion gear that mates with the ring gear on the differential.
A manual transmission has several shafts with various gears and other components attached to them. Most modern passenger cars use 'constant-mesh' transmissions consisting of three shafts: an ''input shaft'', a ''countershaft'' (also called a [[layshaft]]) and an ''output shaft''.<ref>{{cite book |last1=Bosch |first1=Robert |title=Automotive Handbook |date=2004 |publisher=Bentley Publishers |isbn=978-0-8376-0333-9 |page=741 |edition=6th |url=https://books.google.com/books?id=zsRHPwAACAAJ |access-date=10 March 2020 |language=en}}</ref>
 
The ''input shaft'' is connected to the engine and spins at engine speed whenever the clutch is engaged.<ref>{{cite web |title=How Manual Transmissions Work |url=https://auto.howstuffworks.com/transmission2.htm |website=www.howstuffworks.com |access-date=13 March 2020 |language=en |date=1 April 2000}}</ref> The ''countershaft'' has gears of various sizes, which are permanently meshed with the corresponding gear on the input shaft.<ref>{{cite web |title=Basic Anatomy – How The Manual Transmission Works |url=https://www.gotodobbs.com/blog/how-manual-transmission-works/ |website=www.gotodobbs.com |access-date=13 March 2020 |date=29 April 2017}}</ref> The gears on the ''output shaft'' are also permanently meshed with a corresponding gear on the countershaft; however, the output shaft gears are able to rotate independently of the output shaft itself (through the use of bearings located between the gears and the shaft).<ref>{{cite web |title=How It Works: Manual transmissions |url=https://driving.ca/auto-news/news/how-it-works-manual-transmissions |website=www.driving.ca |access-date=13 March 2020 |language=en |date=12 September 2018}}</ref> Through the use of [[Shaft collar|collars]] (operated using the ''shift rods''), the speed of the output shaft becomes temporarily locked to the speed of the selected gear.<ref>{{cite web |title=Manual Transmission Basics |url=https://www.edmunds.com/car-technology/manual-transmission-basics.html |website=www.edmunds.com |access-date=13 March 2020 |language=en-us |date=25 April 2001}}</ref> Some transmission designs—such as in the Volvo 850 and S70—have two countershafts, both driving an output pinion meshing with the front-wheel-drive transaxle's ring gear. This allows for a narrower transmission since the length of each countershaft is halved compared with one that contains four gears and two shifters.
Front-wheel and rear-wheel-drive transmissions operate similarly. When the transmission is in neutral, and the clutch is disengaged, the input shaft, clutch disk and countershaft can continue to rotate under their own inertia. In this state, the engine, the input shaft and clutch, and the output shaft all rotate independently.
 
The fixed and free gears can be mounted on either the input or output shaft or both. For example, a five-speed transmission might have the first-to-second selectors on the countershaft, but the third-to-fourth selector and the fifth selector on the main shaft. This means that when the vehicle is stopped and idling in neutral with the clutch engaged and the input shaft spinning, the third-, fourth-, and fifth-gear pairs do not rotate.
===Dog clutch===
The gear selector does not engage or disengage the actual gear teeth which are permanently meshed. Rather, the action of the gear selector is to lock one of the freely spinning gears to the shaft that runs through its hub. The shaft then spins together with that gear. The output shaft's speed relative to the countershaft is determined by the ratio of the two gears: the one permanently attached to the countershaft, and that gear's mate which is now locked to the output shaft.
 
When neutral is selected, none of the gears on the output shaft are locked to the shaft, allowing the input and output shafts to rotate independently. For reverse gear, an idler gear is used to reverse the direction in which the output shaft rotates. In many transmissions, the input and output shafts can be directly locked together (bypassing the countershaft) to create a 1:1 gear ratio which is referred to as ''direct-drive''.
Locking the output shaft with a gear is achieved by means of a dog clutch selector. The dog clutch is a sliding selector mechanism which is splined to the output shaft, meaning that its hub has teeth that fit into slots (splines) on the shaft, forcing it to rotate with that shaft. However, the splines allow the selector to move back and forth on the shaft, which happens when it is pushed by a selector fork that is linked to the gear lever. The fork does not rotate, so it is attached to a collar bearing on the selector. The selector is typically symmetric: it slides between two gears and has a synchromesh and teeth on each side in order to lock either gear to the shaft.
 
In a transmission for [[longitudinal engine|longitudinal engined]] vehicles (e.g. most rear-wheel-drive cars), it is common for the input shaft and output shaft to be located on the same axis, since this reduces the [[torsion (mechanics)|torsional forces]] to which the transmission casing must withstand. The assembly consisting of both the input and output shafts is referred to as the ''main shaft'' (although sometimes this term refers to just the input shaft or output shaft). Independent rotation of the input and output shafts is made possible by one shaft being located inside the hollow bore of the other shaft, with a bearing located between the two shafts.
===Synchromesh===
If the teeth, the so-called dog teeth, make contact with the gear, but the two parts are spinning at different speeds, the teeth will fail to engage and a loud grinding sound will be heard as they clatter together. For this reason, a modern dog clutch in an automobile has a synchronizer mechanism or ''synchromesh'', where before the teeth can engage, a [[cone clutch]] is engaged which brings the selector and gear to the same speed. Moreover, until synchronization occurs, the teeth are prevented from making contact, because further motion of the selector is prevented by a blocker (or "baulk") ring. When synchronization occurs, friction on the blocker ring is relieved and it twists slightly, bringing into alignment certain grooves and notches that allow further passage of the selector which brings the teeth together. Of course, the exact design of the synchronizer varies from manufacturer to manufacturer.
 
In a transmission for [[transverse engine]]d vehicles (e.g., front-wheel-drive cars), there are usually only two shafts: input and countershaft (sometimes called input and output). The input shaft runs the whole length of the gearbox, and there is no separate input pinion. These transmissions also have an integral [[Differential (mechanical device)|differential]] unit, which is connected via a pinion gear at the end of the counter/output shaft.
The synchronizer<ref>{{cite web|url=http://www.howstuffworks.com/transmission3.htm|title=Synchronizers; graphic illustration of how they work|accessdate=2007-07-18|format= |work= }}</ref> has to change the momentum of the entire input shaft and clutch disk. Additionally, it can be abused by exposure to the momentum and power of the engine itself, which is what happens when attempts are made to select a gear without fully disengaging the clutch. This causes extra wear on the rings and sleeves, reducing their service life. When an experimenting driver tries to "match the revs" on a synchronized transmission and force it into gear without using the clutch, the synchronizer will make up for any discrepancy in RPM. The success in engaging the gear without clutching can deceive the driver into thinking that the RPM of the layshaft and transmission were actually exactly matched. Nevertheless, approximate "rev-matching" ''with clutching'' can decrease the general delta between layshaft and transmission and decrease synchro wear.
 
<gallery caption="Gear selection in a constant-mesh transmission" mode="packed">
===Reverse===
Image:Manual transmission clutch First gear.PNG|First gear (blue, to back)
The previous discussion applies to the forward gears. The implementation of the reverse gear is usually different, implemented in the following way to reduce the cost of the transmission. Reverse is also a pair of gears: one gear on the countershaft and one on the output shaft. However, whereas all the forward gears are always meshed together, there is a gap between the reverse gears. Moreover, they are both attached to their shafts: neither one rotates freely about the shaft. What happens when reverse is selected is that a small gear, called an ''[[gear ratio#idler gears|idler gear]]'' or ''reverse idler'', is slid between them. The idler has teeth which mesh with both gears, and thus it couples these gears together and reverses the direction of rotation without changing the gear ratio.
Image:Manual transmission clutch Second gear.PNG|Second gear (blue, to front)
Image:Manual transmission clutch Third gear.PNG|Third gear (purple, to back)
Image:Manual transmission clutch Fourth gear.PNG|Fourth gear (purple, to front)
</gallery>
<gallery mode="packed">
Image:Manual transmission clutch Reverse gear.PNG|Reverse (green engaged)
Image:Manual transmission clutch Neutral.PNG|Neutral (all disengaged)
</gallery>
 
===Dog clutch===
Thus, in other words, when reverse gear is selected, in fact it '''is''' actual gear teeth that are being meshed, with no aid from a synchronization mechanism. For this reason, the output shaft must not be rotating when reverse is selected: the car must be stopped. In order that reverse can be selected without grinding even if the input shaft is spinning inertially, there may be a mechanism to stop the input shaft from spinning. The driver brings the vehicle to a stop, and selects reverse. As that selection is made, some mechanism in the transmission stops the input shaft. Both gears are stopped and the idler can be inserted between them. There is a clear description of such a mechanism in the [[Honda Civic]] 1996-1998 Service Manual, which refers to it as a "noise reduction system":
In a modern constant-mesh manual transmission, the gear teeth are permanently in contact with each other, and [[dog clutch|dog clutches]] (sometimes called ''dog teeth'') are used to select the gear ratio for the transmission. When the dog clutches for all gears are disengaged (i.e. when the transmission is in neutral), all of the gears are able to spin freely around the output shaft. When the driver selects a gear, the dog clutch for that gear is engaged (via the gear selector rods), locking the transmission's output shaft to a particular gear set. This means the output shaft rotates at the same speed as the selected gear, thus determining the gear ratio of the transmission.<ref>{{cite web |title=How Manual Transmissions Work |url=https://auto.howstuffworks.com/transmission4.htm |website=www.howstuffworks.com |access-date=7 June 2020 |language=en |date=1 April 2000}}</ref>
 
The dog clutch is a sliding selector mechanism that sits around the output shaft. It has teeth to fit into the [[Spline (mechanical)|splines]] on the shaft, forcing that shaft to rotate at the same speed as the gear hub. However, the clutch can move back and forth on the shaft, to either engage or disengage the splines. This movement is controlled by a selector fork that is linked to the gear lever. The fork does not rotate, so it is attached to a collar bearing on the selector. The selector is typically symmetric: it slides between two gears and has a synchromesh and teeth on each side in order to lock either gear to the shaft. Unlike some other types of clutches (such as the foot-operated clutch of a manual-transmission car), a dog clutch provides non-slip coupling and is not suited to intentional slipping.
:Whenever the clutch pedal is depressed to shift into reverse, the mainshaft continues to rotate because of its inertia. The resulting speed difference between mainshaft and reverse idler gear produces gear noise [grinding]. The reverse gear noise reduction system employs a cam plate which was added to the reverse shift holder. When shifting into reverse, the 5th/reverse shift piece, connected to the shift lever, rotates the cam plate. This causes the 5th synchro set to stop the rotating mainshaft. (13-4)
 
==={{Anchor|Synchronized transmission}}Synchromesh===<!-- This subsection is linked from non-synchronous transmission, don't remove anchor! -->
A reverse gear implemented this way makes a loud whining sound, which is not heard in the forward gears. The teeth on the forward gears of consumer automobiles are helically cut. When [[gear#Helical gears|helical gears]] rotate, their teeth slide together, which results in quiet operation. In spite of all forward gears being always meshed, they do not make a sound that can be easily heard above the engine noise. By contrast, reverse gears are [[gear|spur gear]]s, meaning that they have straight teeth, in order to allow for the sliding engagement of the idler, which would not be possible with helical gears. The teeth of spur gears clatter together when the gears spin, generating a characteristic whine.
[[File:Sincronizzatore.jpg|thumb|Synchronizer rings]]
In order to provide smooth gearshifts without requiring the driver to [[double-clutching (technique)|manually match the engine revs]] for each gearshift, most modern passenger car transmissions use 'synchromesh' (also called 'synchronizer rings') on the forward gears. These devices automatically match the speed of the input shaft with that of the gear being selected, thus removing the need for the driver to use techniques such as [[double-clutching (technique)|double-clutching]]. The synchromesh transmission was invented in 1919 by [[Earl Avery Thompson]] and first used on production cars by Cadillac in 1928.<ref>{{cite web|url=https://hooniverse.com/synchromesh-gear-box-hows-that-work/|title=Synchromesh Gear Box- How's That Work?|date=29 April 2014|work=hooniverse.com|access-date=23 September 2019}}</ref>
 
The need for synchromesh in a constant-mesh transmission is that the dog clutches require the input shaft speed to match that of the gear being selected; otherwise, the dog teeth will fail to engage and a loud grinding sound will be heard as they clatter together. Therefore, to speed up or slow down the input shaft as required, cone-shaped brass synchronizer rings are attached to each gear. When the driver moves the gearshift lever towards the next gear, these synchronizer rings press on the cone-shaped sleeve on the dog collar so that the friction forces can reduce the difference in rotational speeds.<ref>{{cite web|url=http://www.howstuffworks.com/transmission3.htm|title=Synchronizers; graphic illustration of how they work|website=Howstuffworks.com|access-date=2007-07-18|date=April 2000}}</ref> Once these speeds are equalized, the dog clutch can engage, and thus the new gear is now in use. In a modern gearbox, the action of all of these components is so smooth and fast it is hardly noticed. Many transmissions do not include synchromesh on the reverse gear (see [[#Reverse gear|Reverse gear]] section below).{{fact|date=February 2023}}
It is clear that the spur gear design of reverse gear represents some compromises&mdash;less robust, unsynchronized engagement and loud noise&mdash;which are acceptable due to the relatively small amount of driving that takes place in reverse. However, many modern transmissions now include a reverse gear synchronizer and helical gearing.
 
The synchromesh system must also prevent the collar from bridging the locking rings while the speeds are still being synchronized. This is achieved through 'blocker rings' (also called 'baulk rings'). The synchro ring rotates slightly because of the frictional torque from the cone clutch. In this position, the dog clutch is prevented from engaging. Once the speeds are synchronized, friction on the blocker ring is relieved and the blocker ring twists slightly, bringing into alignment certain grooves or notches that allow the dog clutch to fall into the engagement.{{fact|date=February 2023}}
===Design Variations===
====Gear Variety====
Manual transmissions are often equipped with 4, 5, or 6 forward gears. Nearly all have one reverse gear. In three or four speed transmissions, in most cases, the topmost gear is "direct", ''i.e.'' a 1:1 ratio. For five speed or higher transmissions, the highest gear is usually an [[overdrive (mechanics)|overdrive]] gear, with a ratio of less than 1:1. Older cars were generally equipped with 3-speed transmissions, or 4-speed transmissions for high performance models and 5-speeds for the most sophisticated of automobiles; in the [[1970s]], 5-speed transmissions began to appear in low priced mass market automobiles and even compact pickup trucks, pioneered by [[Toyota]] (who advertised the fact by giving each model the suffix ''SR5'' as it acquired the fifth speed). Today, mass market automotive manual transmissions are essentially all 5-speeds, with 6-speed transmissions beginning to emerge in high performance vehicles in the early [[1990s]], and recently beginning to be offered on some high-efficiency and conventional passenger cars. A very small number of 7-speed 'manual derived' transmissions are offered on extremely high-end performance cars ([[supercar]]s), such as the Bugatti Veyron 16.4, or the BMW M5. Both of these cars feature a "[[Paddle Shifter]]".
 
Common metals for synchronizer rings are [[brass]] and [[steel]], and are produced either by [[forging]] or sheet metal shaping. The latter involves stamping the piece out of a sheet metal strip and then [[machining]] to obtain the exact shape required. The rings are sometimes coated with anti-wear linings (also called 'friction linings') made from [[molybdenum]], [[iron]], [[bronze]] or [[carbon]] (with the latter usually reserved for high-performance transmissions due to their high cost).<ref>{{cite web |author=Diehl Metall Stiftung & Co. KG |url=http://www.diehl.com/en/diehl-metall/products/synchronizer-rings.html |title=Synchronizer Rings: Diehl Metall |website=Diehl.com |access-date=2017-03-06 |archive-date=7 March 2017 |archive-url=https://web.archive.org/web/20170307203812/http://www.diehl.com/en/diehl-metall/products/synchronizer-rings.html |url-status=dead }}</ref>
====External Overdrive====
On earlier models with three or four forward speeds, the lack of an overdrive ratio for relaxed and fuel-efficient highway cruising was often filled by incorporating a separate [[overdrive (mechanics)|overdrive]] unit in the rear housing of the transmission. This unit was separately actuated by a knob or button, often incorporated into the gearshift knob.
 
Mechanical wear of the synchronizer rings and sleeves can cause the synchromesh system to become ineffective over time. These rings and sleeves have to overcome the momentum of the entire input shaft and clutch disk during each gearshift (and also the momentum and power of the engine, if the driver attempts a gearshift without fully disengaging the clutch). Larger differences in speed between the input shaft and the gear require higher friction forces from the synchromesh components, potentially increasing their wear rate.{{fact|date=February 2023}}
====Shaft and Gear Configuration====
The input shaft need not turn a pinion which rotates the countershaft. Another possibility is that gears are mounted on the input shaft itself, meshed with gears on the countershaft, in which case the countershaft then turns the output shaft. In other words, it's a matter of design on which shaft the driven and driving gears reside.
 
=== Reverse gear ===
The distribution of the shifters is also a matter of design; it need not be the case that all of the free-rotating gears with selectors are on one shaft, and the permanently splined gears on the other. For instance a five speed transmission might have the first-to-second selectors on the countershaft, but the third-to-fourth selector and the fifth selector on the mainshaft, which is the configuration in the 1998 [[Honda Civic]]. This means that when the car is stopped and idling in neutral with the clutch engaged input shaft spinning, the third, fourth and fifth gear pairs do not rotate.
Even in modern transmissions where all of the forward gears are in a constant-mesh configuration, often the reverse gear uses the older ''sliding-mesh'' ("crash box") configuration. This means that moving the gearshift lever into reverse results in gears moving to mesh together. Another unique aspect of the reverse gear is that it consists of two gears—an [[idler gear]] on the countershaft and another gear on the output shaft—and both of these are directly fixed to the shaft (i.e. they are always rotating at the same speed as the shaft). These gears are usually [[spur gear]]s with straight-cut teeth which—unlike the helical teeth used for forward gear—results in a whining sound as the vehicle moves in reverse.
 
When reverse gear is selected, the idler gear is physically moved to mesh with the corresponding gears on the input and output shafts. To avoid grinding as the gears begin to the mesh, they need to be stationary. Since the input shaft is often still spinning due to momentum (even after the car has stopped), a mechanism is needed to stop the input shaft, such as using the synchronizer rings for fifth gear. However, some vehicles do employ a synchromesh system for the reverse gear, thus preventing possible crunching if reverse gear is selected while the input shaft is still spinning.<ref>{{cite web|url=http://www.alfisti.net/311.2.html?&L=1 |title=Buyers Guide Alfa Romeo Spider & GTV 916 |publisher=Alfisti.net |access-date=2010-10-16}}</ref>
In some transmission designs (Volvo 850 and V/S70 series, for example) there are actually two countershafts, both driving an output pinion meshing with the front-wheel-drive transaxle's ring gear. This allows the transmission designer to make the transmission narrower, since each countershaft must be only half as long as a traditional countershaft with four gears and two shifters.
 
Most transmissions include a lockout mechanism to prevent reverse gear from being accidentally selected while the car is moving forwards. This can take the form of a collar underneath the gear knob which needs to be lifted or requiring extra force to push the gearshift lever into the plane of reverse gear.
==Clutch==
In all vehicles using a transmission (virtually all modern vehicles), a coupling device is used to separate the engine and transmission when necessary. The [[clutch]] accomplishes this in manual transmissions. Without it, the engine and tires would at all times be inextricably linked, and anytime the vehicle stopped the engine perforce stall. Without the clutch, changing gears would be very difficult, even with the vehicle moving already: deselecting a gear while the transmission is under load requires considerable force, and selecting a gear requires the revolution speed of the engine to be held at a very precise value which depends on the vehicle speed and desired gear. In a car the clutch is usually operated by a pedal; on a motorcycle, a lever on the left handlebar serves the purpose.
 
=== Non-synchronous transmission ===
[[Image:Pedal Locations in 2007 Subaru Legacy.jpg|thumb|250px|Pedal setup on a 2007 [[Subaru Legacy]]. From left to right, the dead pedal, clutch pedal, brake, and accelerator.]]
{{Main|Non-synchronous transmission}}
[[File:Crash gearbox 3gears and reverse.gif|thumb|right|3-speed non-synchronous "crash" gearbox; used in automobiles pre-1950s and semi-trailer trucks]]
Another design of transmission that is used in older [[car]]s, [[Semi-truck|trucks]], and [[tractor]]s, is a non-synchronous transmission (also known as a crash gearbox). Non-synchronous transmissions use a sliding-mesh (or constant-mesh, in later years) design and have the nickname "crash" because the difficulty in changing gears can lead to gear shifts accompanied by crashing/crunching noises.
{{clear}}
 
== Clutch ==
* When the clutch pedal is fully depressed, the clutch is fully disengaged, and no [[torque]] is transferred from the engine to the transmission (and by extension to the drive wheels). In this uncoupled state it is possible to select gears or to stop the car without stopping the engine.
{{Main article|Clutch}}
* When the clutch pedal is fully released, the clutch is fully engaged, and practically all of the engine's torque is transferred. In this coupled state, the clutch does not slip, but rather acts as rigid coupling, and power is transmitted to the wheels with minimal practical waste heat.
[[File: Tuning World Bodensee 2018, Friedrichshafen (OW1A1318).jpg|left|thumb|Exploded view of a flywheel, friction disk, and clutch kit]]
* Between these extremes of engagement and disengagement the clutch slips to varying degrees. When the clutch slips it still transmits torque despite the difference in speeds between the engine crankshaft and the transmission input. Because this torque is transmitted by means of friction rather than direct mechanical contact, considerable power is wasted as heat (which is dissipated by the clutch). Properly applied, slip allows the vehicle to be started from a standstill, and when it is already moving, allows the engine rotation to gradually adjust to a newly selected gear ratio.
Vehicles with manual transmissions use a clutch to manage the linkage between the engine and the transmission, and decouple the transmission from the engine during gearshifts and when the vehicle is stationary. Without a clutch, the engine would stall any time the vehicle stopped, and changing gears would be difficult (deselecting a gear while the transmission requires the driver to adjust the throttle so that the transmission is not under load, and selecting a gear requires the engine RPM to be at the exact speed that matches the road speed for the gear being selected).
* Because of the heat that a slipping clutch generates, slip should not be maintained beyond necessity; skilled drivers rarely allow a clutch to slip for more large fraction of a second or so. {{Fact|date=October 2007}} Learning to use the clutch efficiently requires the development of [[muscle memory]] and a level of coordination analogous to that required to learn a musical instrument or to play a sport.
* A rider of a highly-tuned motocross or off-road motorcycle may "hit" or "fan" the clutch when exiting corners to assist the engine in revving to the point where it delivers the most power.
*Note: Automatic transmissions also use a coupling device; however, a clutch is not present. In these kinds of vehicles, the [[torque converter]] is used to separate the engine and transmission.
 
Most motor vehicles use a [[automobile pedal|pedal]] to operate the clutch; except for motorcycles, which usually have a clutch lever on the left [[Motorcycle handlebar|handlebar]].
==Gear selection==
{{clear}}
===Floor-mounted shifter===
In most modern passenger cars, gears are selected through a lever attached to the floor of the automobile&mdash;this selector is often called a '''[[gearstick]]''', '''gear lever''', '''gear selector''', or simply '''shifter'''. Moving this lever forward, backward, left, and right allows the driver to select any given gear. In this configuration, the gear lever must be pushed laterally before it is pushed longitudinally.
 
== Gear shift types ==
[[Image:Shift stick.jpg|thumb|250px|5 speed shift stick of a 1999 [[Mazda Protege]].]]
{{Main article|Gear stick}}
[[File:shift stick.jpg|thumb|right|Floor-mounted gear stick in a [[Mazda Protege]] passenger car]]
[[File:Manual Layout.svg|thumb|left|upright=0.75|Common shift pattern for a 5-speed transmission]]
 
In most vehicles with a manual transmission, the driver selects gears by manipulating a lever called a ''gear stick'' (also called a ''gearshift'', ''gear lever'' or ''shifter''). In most automobiles, the gear stick is located on the floor between the driver and front passenger, but some cars have a gear stick that is mounted to the steering column or center console.
A sample layout of a ''four-speed'' transmission is shown below. '''N''' marks ''neutral'', or the position where no gears are engaged. In reality, the entire horizontal line is a ''neutral'' position, although the shifter is usually equipped with springs so that it will return to the N position if not left in another gear. The '''R''' denotes reverse, which is technically a fifth gear on this transmission.
 
The movement of the gear stick is transferred (via solid linkages or cables) to the selector forks within the transmission.
[[Image:Manual Layout4d.PNG]]
 
Motorcycles typically employ [[sequential manual transmission]]s, although the shift pattern is modified slightly for safety reasons. Gear selection is usually via the left-foot (or, on older motorcycles, right-foot) shift lever with a layout of {{nobr|1–N–2–3–4–5–6.}}
This layout is called the '''shift pattern'''. Because of the shift quadrants, the basic arrangement is often called an ''H-pattern''. While the layout for gears one through four is nearly universal, the ___location of reverse is not. Reverse can be found outside of the quadrant at the upper left (late 1960s [[General Motors Corporation|GM]] models and AMC models, 1960s-1980s Ford Europe models, and current VW/Audi models), lower left ([[Toyota FJ Cruiser|Fj Cruiser]], [[Ferrari]]), the lower right (Jeep CJ7, Datsun models, and [[Honda Civic]]), or upper right ([[Chevrolet Corvette|Corvette]]), so caution is always warranted in gear selection. The shift pattern for a specific transmission is usually molded on the [[gear knob]].
 
=== "Three on the tree" vs. "four on the floor" ===
The image below shows the most common five-speed layout found in the USA and the UK.
During the period when U.S. vehicles usually had only three forward speeds, the most common gear-shifter ___location was on the steering column, a layout that was sometimes called "three on the tree". By contrast, high-performance cars, and European vehicles in general, mostly used a four-speed transmission with floor-mounted shifters. That layout was referred to as "four on the floor".
 
Most [[FR layout|FR (front-engined, rear-wheel drive)]] vehicles have a transmission that sits between the driver and the front passenger seat. Floor-mounted shifters are often connected directly to the transmission. [[FF layout|FF (front-engined, front-wheel drive)]] vehicles, [[RR layout|RR (rear-engined, rear-wheel drive)]] vehicles and front-engined vehicles with rear-mounted gearboxes often require a mechanical linkage to connect the shifter to the transmission.
[[Image:Manual Layout.PNG]]
 
=== {{anchor|Three on the tree|Column-mounted shifter|Column shift|Column}} Column-mounted shifter ===
This layout is reasonably intuitive because it starts at the upper left and works top to bottom, left to right, with reverse far away and toward the rear of the car. There is usually a mechanism that only allows selection of reverse from the neutral position, so reverse will be less likely to be accidentally chosen when downshifting from 5th to 4th (or by someone used to a 6-speed transmission and trying to shift from 5th to the non-existent 6th).
 
[[File:SAAB96-interior.jpg|thumb|right|Column mounted gear shift lever in a [[Saab 96]]]]
[[Image:Manual Dogleg.png]]
 
Some vehicles have a gear lever mounted on the steering column. A 3-speed column shifter, which came to be popularly known as a "three on the tree", began appearing in America in the late 1930s and became common during the 1940s and 1950s. If a U.S. vehicle was equipped with [[overdrive (mechanics)|overdrive]], it was very likely to be a [[Borg-Warner]] type, operated by briefly backing off the accelerator pedal when above {{convert|28|mph|abbr=on}} to enable, and momentarily flooring the same pedal to return to normal gear. The control simply disables overdrive for such situations as parking on a hill or preventing unwanted shifting into overdrive.{{citation needed|date=April 2012}}
This five-speed layout, found on many race cars and some older model passenger cars, is commonly referred to as a "dog-leg first" or "racing" pattern, because of the "up and over" 1-2 shift. Its use is common in race cars and sports cars, but is deminishing as six speed and sequential gearboxes are becoming more common. Having 1st gear across the dog leg is beneficial as first gear is traditionally only used for getting the car moving and hence it allows 2nd and 3rd gear to be in the same vertical plane, which makes downshifting into 2nd gear easier. As most of the gearboxes are non-syncromesh there is no appreciable delay when upshifting from 1st through the dog leg into 2nd.
 
[[File:Manual Layout 3.svg|125px]]
This gear pattern can also be found on some heavy vehicles where 1st gear is a crawler gear and would see little normal use.
 
Later, European and Japanese models began to have 4-speed column shifters with this shift pattern:
Another five-speed shift pattern (common on many European cars) is this:
 
[[File:Column4MT.svg|125px]]
[[Image:Manual Layout 2.PNG]]
 
A majority of North American-spec vehicles sold in the U.S. and Canada had a 3-speed column-mounted shifter—the first generation Chevrolet/GMC vans of 1964–70 vintage had an ultra-rare 4-speed column shifter. The column-mounted manual shifter disappeared in North America by the mid-1980s, last appearing in the 1987 [[Chevrolet Scottsdale|Chevrolet pickup truck]]. Prior to 1980, the GM X platform compacts (Chevrolet Nova and its rebadged corporate clones) were the final passenger cars to have a column-mounted manual shifter. Outside North America, the column-mounted shifter remained in production. All [[Toyota Crown]] and [[Nissan Cedric]] [[taxicabs of Hong Kong|taxis in Hong Kong]] had the 4-speed column shift until 1999 when automatic transmissions were first offered. Since the late 1980s or early 1990s, a 5-speed column shifter has been offered in some vans sold in Asia and Europe, such as [[Toyota Hiace]], [[Mitsubishi Delica|Mitsubishi L400]] and the first-gen [[Fiat Ducato]]. Many European cars had manual column shifts and the Renault 16TX had a 5 speed.
Transmissions equipped with this shift pattern usually feature a lockout mechanism that requires the driver to depress a switch or the entire gear lever when entering reverse, so that reverse is not accidentally selected when trying to find first gear. This style of pattern (including depressing the gear lever) is common on BMWs, Opels, most Volkswagens (though some have reverse towards second gear,) older Volvo 240s and some Renault models (12, 9, 19, 5, Mégane, Twingo and Clio).
 
Column shifters are mechanically similar to floor shifters, although shifting occurs in a vertical plane instead of a horizontal one. Because the shifter is further away from the transmission, and the movements at the shifter and at the transmission are in different planes, column shifters require more complicated [[linkage (mechanical)|linkage]] than floor shifters. Advantages of a column shifter are the ability to switch between the two most commonly used gears—second and third—without letting go of the steering wheel, and the lack of interference with passenger seating space in vehicles equipped with a [[bench seat]].
A typical pattern for the more modern six-speed transmission is shown here
 
===Console-mounted shifter===
[[Image:Manual Layout6.png]]
Some smaller cars in the 1950s and 1960s, such as [[Citroën 2CV]], [[Renault 4]] and early [[Renault 5]] feature a shifter in the dash panel. This was cheaper to manufacture than a column shifter and more practical, as the gearbox was mounted in front of the engine. The linkage for the shifter could then be positioned on top of the engine. The disadvantage is that shifting is less comfortable and usually slower to operate.
 
Newer small cars and [[minivan|MPV]]s, like the [[Suzuki MR Wagon]], the [[Fiat Multipla]], the [[Toyota Matrix]], the [[Pontiac Vibe]], the [[Chrysler RT platform]] cars, the [[Honda Element]], the [[Honda Civic]], the [[Daihatsu Sigra]], and the [[Honda Avancier]], may feature a manual or [[automatic transmission]] gear shifter located on the vehicle's instrument panel, similar to the mid-1950s [[PowerFlite|Chryslers]] and [[Powerglide]] [[Chevrolet Corvair|Corvair]]s. Console-mounted shifters are similar to floor-mounted gear shifters in that most of the ones used in modern vehicles operate on a horizontal plane and can be mounted to the vehicle's transmission in much the same way a floor-mounted shifter can. However, because of the ___location of the gear shifter in comparison to the locations of the column shifter and the floor shifter, as well as the positioning of the shifter to the rest of the controls on the panel often require that the gearshift be mounted in a space that does not feature a lot of controls integral to the vehicle's operation, or frequently used controls, such as those for the [[car stereo|stereo system]] or [[car air conditioning|HVAC system]], to help prevent accidental activation or driver confusion.
A six-speed manual transmission (seven speeds with reverse) is widely considered to be the largest number of gears that can be contained within a variation of the "H" shift pattern. Note that reverse is placed outside of the "H", with a canted shift leg. This is to prevent the shift lever from intruding too far into the driver's footwell (in [[Driving on the left or right|left-hand drive]] cars) when reverse is selected. This is the most common layout for a six-speed manual transmission.
 
More and more small cars and vans from manufacturers such as [[Suzuki]], [[Honda]], and [[Volkswagen]] are featuring console shifters in that they free up space on the floor for other features such as storage compartments without requiring that the gear shift be mounted on the steering column. Also, the basic ___location of the gear shift in comparison to the column shifter makes console shifters easier to operate than column shifters.
Most [[FR layout|front-engined, rear-wheel drive]] cars have a transmission that sits between the driver and the front passenger seat. Floor-mounted shifters are often connected directly to the transmission. [[FF layout|Front-wheel drive]] and [[RR layout|rear-engined]] cars often require a mechanical linkage to connect the shifter to the transmission.
{{clear left}}
 
== External overdrive ==
Historically, 4-speed floor shifters were sometimes referred to as "Four on the Floor", when steering column mounted shifters were more common.
{{Main article|overdrive (mechanics)|l1=Overdrive}}
In the 1950s, 1960s, and 1970s, fuel-efficient highway cruising with low engine speed was in some cases enabled on vehicles equipped with 3- or 4-speed transmissions by means of a separate [[overdrive (mechanics)|overdrive]] unit in or behind the rear housing of the transmission. This was actuated either manually while in high gear by throwing a switch or pressing a button on the gearshift knob or on the steering column, or automatically by momentarily lifting the foot from the accelerator with the vehicle traveling above a certain road speed. Automatic overdrives were disengaged by flooring the accelerator, and a lockout control was provided to enable the driver to disable overdrive and operate the transmission as a normal (non-overdrive) transmission.<ref>{{cite web|url=http://www.fordification.com/tech/overdrive.htm |title=The Borg-Warner Overdrive Transmission Explained |publisher=FORDification.com |access-date=2012-04-22}}</ref>
 
The term 'overdrive' is also used to describe a gear with a ratio of less than one (e.g., if the top gear of the transmission has a ratio of 0.8:1).
===Column-mounted shifter===
Some cars have a gear lever mounted on the steering column of the car. It was common in the past but is no longer common today. However, many automatic transmissions still use this placement.
 
== Push starting ==
Column shifters are mechanically similar to floor shifters, although shifting occurs in a vertical plane instead of a horizontal one. Column shifters also generally involve additional linkages to connect the shifter with the transmission. Also, the pattern is not "[[intuitive]]," as the shifter has to be moved backward and upward into R to make the car go backward.
Vehicles with a manual transmission can often be [[push start]]ed when the starter motor is not operational, such as when the car has a dead battery or when the starter motor itself has malfunctioned and is unable to deliver sufficient rotational energy to turn the engine over.
 
When push-starting, the energy generated by the wheels moving on the road is transferred to the driveshaft, then the transmission, and eventually the crankshaft. When the crankshaft spins as a result of the energy generated by the rolling of the vehicle, the motor is cranked over. This simulates what the starter is intended for and operates in a similar way to crank handles on very old cars from the early 20th century, with the cranking motion being replaced by the pushing of the car.
A 3-speed column shifter, nicknamed "Three on the Tree" (alternatively, "Three in the Tree"), began appearing in America in the late 1930s and became common during the 1940s and '50s. Its layout is as shown below:
 
== Driving techniques ==
[[Image:Manual Layout 3.PNG]]
Recently, many automatic transmissions have included more gear ratios than their manual counterparts.<ref>{{cite web |title=Here's what's really killing the manual transmission |url=https://www.roadandtrack.com/car-culture/a6308/whats-really-killing-the-manual-transmisson/ |website=roadandtrack.com |access-date=17 June 2020 |date=10 March 2014}}</ref><ref>{{cite web |title=Why the 2018 Ford Mustang GT Automatic is So Much Quicker Than the Manual |url=https://www.motortrend.com/news/why-the-2018-ford-mustang-gt-automatic-is-so-much-quicker-than-the-manual/ |website=motortrend.com |date=22 June 2018 |access-date=17 June 2020}}</ref>
 
In some countries, a driving license issued for vehicles with an automatic transmission is not valid for driving vehicles with a manual transmission, but a license for manual transmissions covers both.<ref>{{cite web|url=https://www.gov.uk/driving-licence-categories|title=Driving licence categories - GOV.UK|website=Gov.uk|access-date=6 March 2017}}</ref>
First gear in a 3-speed is often called "low," while third is usually called "high." There is, of course, no overdrive. Later European and Japanese models began to have 4-speed column shifter and some of these made their way to the USA. Its layout is shown here:
 
=== Hill starts ===
[[Image:Column4MT.PNG]]
Starting from a stationary position in a manual transmission vehicle requires extra torque to accelerate the vehicle up the hill, with the potential for the vehicle to roll backward in the time it takes to move the driver's foot from the brake pedal to the accelerator pedal (to increase the engine RPM before engaging the clutch). A traditional method of hill starts in a manual transmission car is to use the [[parking brake]] (also called "handbrake", "emergency brake", or "e-brake") to hold the vehicle stationary. This means that the driver's right foot is not needed to operate the brake pedal, freeing it up to be used on the accelerator pedal instead. Once the required engine RPM is obtained, the driver can engage the clutch, also releasing the parking brake as the clutch engages.
 
A device called the [[hill-holder]] was introduced on the 1936 Studebaker. Many modern vehicles use an electronically actuated parking brake, which often includes a hill-holder feature whereby the parking brake is automatically released as the driven wheels start to receive power from the engine.<ref>{{cite web|last=Lampton |first=Christopher |url=http://auto.howstuffworks.com/car-driving-safety/safety-regulatory-devices/hill-start-control.htm |title=How Hill-Start Control Works &#124; HowStuffWorks |website=Auto.howstuffworks.com |date=2009-10-05 |access-date=2017-03-06}}</ref>
However, the column manual shifter disappeared in America by the late 1970s. But in the rest of the world, the column mounted shifter continued to be made, and was in fact common in some places. For example, all [[Toyota Crown]] and [[Nissan Cedric]] [[taxicabs of Hong Kong|taxis in Hong Kong]] had the 4-speed column shift until 1999 when automatic began to be offered. Since the late 1980s or early 1990s, 5-speed column shifter has been made in some vans sold in Asia and Europe, such as [[Toyota Hiace]] and [[Mitsubishi Delica|Mitsubishi L400]].
 
In many light-duty vehicles, skilled drivers can slip the clutch just barely enough to hold the vehicle from much rollback during the second while the right foot is moving from the brake pedal to the accelerator pedal; this method effectively solves the hill-holding problem without any parking brake use and with negligible clutch life reduction, although it requires some skill.
===Sequential manual===
Some transmissions do not allow the driver to arbitrarily select any gear. Instead, the driver may only ever select the next-lowest or next-highest gear ratio. These transmissions often provide clutch control, but the clutch is only necessary when selecting first or reverse gear from neutral. Most gear changes can be performed without the clutch.
 
On vehicles with a hand throttle such as [[tractor|agricultural tractors]], it is possible to avoid rollback by increasing engine RPM using the hand throttle, then releasing the brake and clutch pedals in the usual fashion.
Sequential transmissions are generally controlled by a forward-backward lever, foot pedal, or set of paddles mounted behind the steering wheel. In some cases, these are connected mechanically to the transmission. In many modern examples, these controls are attached to sensors which instruct a transmission computer to perform a shift&mdash;many of these systems can be switched into an automatic mode, where the computer controls the timing of shifts, much like an [[automatic transmission]].
 
=== Other driving techniques {{anchor|rev_matching|rowing|block_shifting|skip_shifting}} ===
Motorcycles typically employ sequential transmissions, although the shift pattern is modified slightly for safety reasons. In a motorcycle the gears are usually shifted with the left foot pedal, the layout being this:
* '''Rev-matching''' is where the driver uses the throttle to match the revs to the road speed so that gear changes are not jerky. This is commonly used by drivers with non-synchromesh gearboxes, or those driving racing vehicles<ref>{{cite web|url=https://flowracers.com/blog/perfect-rev-matching/#:~:text=Rev%20matching%20works%20by%20matching,when%20the%20clutch%20is%20released.&text=This%20means%20that%20the%20car,acceleration%20out%20of%20the%20corner. |title=The 5 Steps To Perfect Rev Matching – The Ultimate Guide |date=29 May 2020 |publisher=FlowRacers.com |access-date=2020-10-01}}</ref>
* '''[[Double-clutching (technique)|Double-clutching]]''' is required on non-synchro gearboxes. To double-clutch while downshifting: depress the clutch pedal and move the gear lever to neutral, release the clutch pedal, "blip" the throttle to speed up the layshaft to increase the rotational speed of the lower gear, depress the clutch pedal again, move the gear lever to the lower gear, then release the clutch pedal.
* '''[[Heel-and-toe shifting]]''' is where the driver uses one foot to modulate the brake and accelerator pedal simultaneously to allow for rev matching under braking.
* '''Rowing''', '''block shifting''' or '''skip shifting'''<ref>{{Cite web|url=https://www.drivingtests.co.nz/resources/why-do-trucks-have-a-lot-of-gears/|title=Why do trucks have a lot of gears}}</ref> is the technique of downshifting more than one gear in order to reduce wear and tear on the gearbox. Rev-matching may need to be used to create a smooth shift. Combining this with Heel-and Toe downshifting provides for maximum braking when going from top gear to a much lower gear, and optimal engine RPM for exiting the corner.
 
== Synchronized downshift rev-matching system ==
[[Image:2003 SV650S Gearshift.jpg|thumb|250px|The gear shift lever on a 2003 [[Suzuki SV650S]] motorcycle.]]
The [[synchronized down shift rev-matching system]] is a computer-controlled technology that mimics the manual rev-matching technique.
 
== Truck transmissions ==
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;6<br>
Some trucks have transmissions that look and behave like ordinary consumer vehicle transmissions, operated by a single lever. These transmissions are used on lighter trucks, typically have up to 6 gears, and usually have [[#Synchromesh|synchromesh]].
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;5&nbsp;┘<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;4&nbsp;┘<br>
&nbsp;&nbsp;&nbsp;&nbsp;3&nbsp;┘<br>
&nbsp;&nbsp;2&nbsp;┘<br>
N<br>
1<br>
 
For trucks needing more gears, the standard "H" pattern can be complicated for some truck drivers, so additional controls are used to select additional gears. The "H" pattern is retained, then an additional control selects among alternatives. In older trucks, the control is often a separate lever mounted on the floor or more recently a pneumatic switch mounted on the "H" lever; in newer trucks, the control is often an electrical switch mounted on the "H" lever. Multi-control transmissions are built in much higher power ratings but rarely use synchromesh.
The pedal goes one step - both up and down - from the center, before it reaches its limit and has to be allowed to move back to the center position. Thus, changing multiple gears in one direction is accomplished by repeatedly pumping the pedal, either up or down. Although neutral is listed as being between first and second gears for this type of transmission, it "feels" more like first and second gear are just "further away" from each other than any other two sequential gears. Because this can lead to difficulty in finding neutral for inexperienced riders most motorcycles have a neutral indicator light on the instrument panel to help finding the neutral gear. The reason neutral does not actually have its own spot in the sequence is to make it quicker to shift from first to second when moving. You will not accidentally shift into neutral. The reason for having neutral between the first and second gears instead of at the bottom is that when stopped, the rider can just click down repeatedly and know that they will end up in first and not neutral.
 
There are several common alternatives for the shifting pattern. The standard types are:
On motorcycles used on race tracks, the shifting pattern is often reversed, that is, the rider clicks down to upshift. This usage pattern increases the [[ground clearance]] by placing the riders foot above the shift lever when the rider is most likely to need it, namely when leaning over and exiting a tight turn.
 
*'''Range transmissions''' use an "H" pattern through a narrow range of gears, then a "range" control shifts the "H" pattern between high and low ranges. For example, an 8-speed range transmission has an H shift pattern with four gears. The first through fourth gears are accessed when a low range is selected. To access the fifth through eighth gears, the range selector is moved to high range, and the gear lever again shifted through the first through fourth gear positions. In high range, the first gear position becomes fifth, the second gear position becomes sixth, and so on.
The shift pattern for most [[underbone]] motorcycles with automatic [[centrifugal clutch]] is also modified for 2 key reasons - to enable the less-experienced riders to shift the gears without problems of "finding" the neutral gear, and also due to more force needed to "lift" the gearshift lever (because gearshift pedal of an underbone motorcycle also operates the clutch). The gearshift lever of an underbone motorcycle has two ends, therefore the rider clicks down the front end with the left toe all the way to the top gear and clicks down the rear end with the heel all the way down to neutral. Some underbone models such as [[Honda Wave series|Honda Wave]] have "rotary" shift pattern, which means that the rider can shift directly to neutral from the top gear, but this is only possible when the motorcycle is stationary for safety reasons. Some models also have gear position indicators for all gear positions at the instrument panel.
*'''Splitter transmissions''' use an "H" pattern with a wide range of gears, and the other selector splits each sequential gear position in two: First gear is in the first position/low split, second gear is in the first position/high split, third gear is in second position/low split, fourth gear is in second position/high split, and so on.
*'''Range-splitter transmissions''' combine range-splitting and gear-splitting. This allows even more gear ratios. Both a range selector and a splitter selector are provided.
 
Although there are many gear positions, shifting through gears usually follows a regular pattern. For example, a series of upshifts might use "move to splitter direct; move to splitter overdrive; move the shift lever to No.&nbsp;2 and move splitter to underdrive; move splitter to direct; move splitter to overdrive; move the shifter to No.&nbsp;3 and move splitter to underdrive"; and so on. In older trucks using floor-mounted levers, a bigger problem is common gearshifts require the drivers to move their hands between shift levers in a single shift, and without synchromesh, shifts must be carefully timed or the transmission will not engage. For this reason, some splitter transmissions have an additional "under under" range, so when the splitter is already in "under" it can be quickly downshifted again, without the delay of a double shift.
===Semi-manual===
Some new transmissions ([[Fiat]]'s ''Selespeed'' gearbox and [[BMW]]'s ''Sequential Manual Gearbox'' (SMG) for example) are conventional manual transmissions with a computerized control mechanism. These transmissions feature independently selectable gears but do not have a [[clutch]] pedal. Instead, the transmission computer controls a [[servo]] which [[wikt:disengage|disengage]]s the clutch when necessary.
 
Modern truck transmissions are most commonly "range-splitter". The most common 13-speed has a standard H pattern, and the pattern from the left upper corner is as follows: R, down to L, over and up to 1, down to 2, up and over to 3, down to 4. The "butterfly" range lever in the center front of the knob is flipped up to high range while in 4th, then shifted back to 1. The 1 through 4 positions of the knob is repeated. Also, each can be split using the thumb-actuated under-overdrive lever on the left side of the knob while in high range. The "thumb" lever is not available in low range, except in 18 speeds; 1 through 4 in the low range can be split using the thumb lever and L can be split with the "Butterfly" lever. L cannot be split using the thumb lever in either the 13- or 18-speed. The 9-speed transmission is like a 13-speed without the under-overdrive thumb lever.
These transmissions vary from sequential transmissions in that they still allow nonsequential shifts: BMWs SMG system, for example, can shift from 6<sup>th</sup> gear directly to 4<sup>th</sup> gear when decelerating from high speeds.
 
Truck transmissions use many physical layouts. For example, the output of an N-speed transmission may drive an M-speed secondary transmission, giving a total of N*M gear combinations. Transmissions may be in separate cases with a shaft in between; in separate cases bolted together; or all in one case, using the same lubricating oil. The second transmission is often called a "Brownie" or "Brownie box" after a popular brand. With a third transmission, gears are multiplied yet again, giving greater range or closer spacing. Some trucks thus have dozens of gear positions, although most are duplicates. Sometimes a secondary transmission is integrated with the differential in the rear axle, called a "two-speed rear end". Two-speed differentials are always splitters. In newer transmissions, there may be two counter shafts, so each main shaft gear can be driven from one or the other countershaft; this allows construction with short and robust countershafts, while still allowing many gear combinations inside a single gear case.
==Comparison with automatic transmissions==
Manual transmissions are typically compared to [[automatic transmissions]], as the two represent the majority of options available to the typical consumer. These comparisons are general guidelines and may not apply in certain circumstances. Additionally, the recent popularity of semi-manual and [[semi-automatic transmission|semi-automatic]] transmissions renders many of these points obsolete. It should be kept in mind that some of these points are true of "conventional" automatic transmissions which shift gears and are coupled to the engine with a [[torque converter]] but are not a true comparison or do not apply to other kinds of automatic transmissions, like the [[continuously-variable transmission]].
 
Heavy-duty transmissions are mostly [[non-synchronous transmission|non-synchromesh]]. Sometimes synchromesh adds weight that could be payload, and is one more thing to fail, and drivers spend thousands of hours driving so can take the time to learn to drive efficiently with a non-synchromesh transmission. [[Float shifting]] (also called "floating gears") is changing gears without disengaging the clutch, usually on a non-synchronized transmission used by large trucks. Since the clutch is not used, it is easy to mismatch speeds of gears, and the driver can quickly cause major (and expensive) damage to the gears and the transmission.
===Advantages===
* Manual transmissions typically offer better fuel economy compared to automatics.<ref name="fueleconomy">The [http://www.fueleconomy.gov United States Department of Energy website] is dedicated to providing information about the fuel consumption of many makes and models of vehicles, with separate entries for the manual and automatic transmission variants of a model, if they exist. The site's [http://www.fueleconomy.gov/feg/tech_transmission.shtml#amt Transmission Technologies] page states that "Manual transmissions are lighter than conventional automatic transmissions and suffer fewer energy losses." </ref> Increased fuel economy with a properly operated manual transmission vehicle versus an equivalent automatic transmission vehicle can range from 5% to about 15% depending on driving conditions and style of driving -- extra urban or urban (highway or city). There are several reasons for this:
** Mechanical efficiency. The manual transmission couples the engine to the transmission with a rigid clutch instead of a [[torque converter]] that introduces significant power losses. The automatic transmission also suffers parasitic losses by driving the high pressure hydraulic pumps required for its operation.
** Fuel cut-off. The torque converter of the automatic transmission is designed for transmitting power from the engine to the wheels. Its ability to transmit power in the reverse direction is limited. During deceleration, if the torque converter's rotation drops beneath its stall speed, the momentum of the car can no longer turn the engine, requiring the engine to be idled. By contrast, a manual transmission, with the clutch engaged, can use the car's momentum to keep the engine turning, in principle, all the way down to zero RPM. This means that there are better opportunities, in a manual car, for the electronic control unit (ECU) to impose deceleration fuel cut-off (DFCO), a fuel-saving mode whereby the fuel injectors are turned off if the throttle is closed (foot off the accelerator pedal) and the engine is being driven by the momentum of the vehicle.
** Geartrain efficiency. Automatics may require power to be transmitted through multiple planetary gearsets before attaining the desired gear ratio.
* Manual transmissions are still more efficient than belt-driven continuously-variable transmissions.<ref>[http://staff.bath.ac.uk/enssa/thesis.pdf An Investigation into The Loss Mechanisms associated with a Pushing Metal V-Belt Continuously Variable Transmission], Sam Akehurst, 2001, Ph. D Thesis, University of Bath.
:''Despite these theoretical predictions to date reduced fuel consumptions and emissions have not been realised by production cars fitted with CVTs. Rather fuel economy figures compared to equivalent fixed ratio vehicles have been at best equal and in most cases considerably lower.'' (p. 1-2)</ref><ref name=
efficiency>[http://www.sae.org/servlets/productDetail?PROD_TYP=PAPER&PROD_CD=1999-01-1259 An Overview of Current Automatic, Manual and Continuously Variable Transmission Efficiencies and Their Projected Future Improvements], Kluger and Log, SAE 1999-01-1259
:This publication assigns 94% efficiency to current 5 speed manual transmissions, 70-80% efficiency (city-highway) to a current four-speed automatics, and predicts 88% efficiency for future continuously-variable designs.</ref>
* Manual transmissions are generally significantly lighter than torque-converter automatics.<ref name="fueleconomy"/>
* Vehicles with manual transmissions are typically less expensive than those with automatic transmissions.
* Manual transmissions normally do not require active cooling, because not much power is dissipated as heat through the transmission.<ref name="efficiency"/>
** The heat issue can be important in certain situations, like climbing long hills in hot weather, particularly if pulling a load. Unless the automatic's torque converter is locked up (which typically only happens in an overdrive gear that would not be engaged when going up a hill) the transmission can overheat.<ref>[http://autos.yahoo.com/maintain/repairqa/transmission/ques123_0.html Car Repair and Maintenance on Yahoo]
:Extended discusson about automatic transmission overheating issues.</ref> A manual transmission's clutch only generates heat when it slips, which does not happen unless the driver is [[riding the clutch]] pedal.
* A driver has more direct control over the state of the transmission with a manual than an automatic. This control is important to an experienced, knowledgeable driver who knows the correct procedure for executing a driving maneuver, and wants the machine to realize his or her intentions exactly and instantly. Manual transmissions are particularly advantageous for performance driving or driving on steep and winding roads. Note that this advantage applies equally to manual-automatic transmissions, such as tiptronic, provided they have a quick reaction time to driver input.
** An example: the driver, anticipating a turn, can downshift to the appropriate gear while the steering is still straight, and stay in gear through the turn. This is the correct, safe way to execute a turn. An unanticipated change of gear during a sharp turn can cause skidding if the road is slippery.
** Another example: when starting, the driver can control how much torque goes to the tires, which is useful for starting on slippery surfaces such as ice, snow or mud. This can be done with clutch finesse, or possibly by starting in second gear instead of first. The driver of an automatic can only put the car into drive, and play with the throttle. The torque converter can easily dump too much torque into the wheels, because when it slips, it acts as an extra low gear, passing through the engine power, reducing the rotations while multiplying torque. Some cars, such as the [[Saab Automobile|Saab]] NG900 Automatic transmission, have a special mode for low traction situations.
** Yet another example: passing. When the driver is attempting to pass a slower moving vehicle by making use of a lane with opposite traffic, he or she can select a lower gear for more power at exactly the right moment when conditions are right to begin the maneuver. Automatics have a delayed reaction time, because the driver can only indicate his intent by pressing the throttle. The skilled manual transmission driver has an advantage of superior finesse and confidence in such situations.{{Fact|date=October 2007}}
* Driving a manual requires more involvement from the driver, thereby discouraging some dangerous practices. The manual selection of gears requires the driver to monitor the road and traffic situation, anticipate events and plan a few steps ahead. If the driver's mind wanders from the driving task, the machine will soon end up in an incorrect gear, which will be obvious from excessive or insufficient engine RPM. Related points:
** It's much more difficult for the driver to fidget in a manual transmission car, for instance by eating, drinking beverages, or talking on a cellular phone without a headset. During gear shifts, two hands are required. One stays on the wheel, and the other operates the gear lever. The hand on the wheel is absolutely required during turns, and tight turns are accompanied by gear changes. If the hand leaves the wheel, the steering will begin to straighten. In general, the more demanding the driving situation, the more difficult it is for the manual driver to do anything but operate the vehicle. The driver of an automatic transmission can engage in distracting activities in any situation, such as sharp turns through intersections or stop-and-go traffic.
** The driver of a manual transmission car can develop an accurate intuition for how fast the car is traveling, from the sound of the motor and the gear selection. It's easier to observe the lower speed limits&mdash;like 30 km/h and 50 km/h or their [[U.S. customary unit|U.S.]] and [[Imperial unit|Imperial]] counterparts, 20 mph and 30 mph&mdash;without glancing at the instrumentation.{{Fact|date=October 2007}}
* Cars with manual transmissions can often be started when the battery is dead by pushing the car into motion or allowing it to roll downhill, and then engaging the clutch in third or second gear. This is commonly known as a "push start", "popping the clutch" (in the USA), "crash starting" (in New Zealand), "roll starting" (in Australia) or "[[bump starting]]" (in the UK). However, this practice is strongly discouraged by most manufacturers, citing possible damage to emissions control devices such as the [[catalytic converter]].
* Manual transmissions work regardless of the orientation angle of the car with respect to gravity. Automatic transmissions have a fluid reservoir (pan) at the bottom; if the car is tilted too much, the fluid pump can be starved, causing a failure in the hydraulics.
* It is sometimes possible to move a vehicle with a manual transmission just by putting it in gear and cranking the starter. This is useful in an emergency situation where the vehicle will not start, but must be immediately moved (from an intersection or railroad crossing, for example). It is also easier to put a car with a manual transmission into neutral, even when the transmission has suffered damage from an accident or malfunction. Many modern vehicles will not allow the starter to be run without the clutch fully depressed, negating this advantage, but some manufacturers have begun to add a clutch start override switch so that this advantage may still be enjoyed when necessary.
 
Heavy trucks are usually powered with [[diesel engine]]s. Diesel truck engines from the 1970s and earlier tend to have a narrow power band, so they need many close-spaced gears. Starting with the 1968 [[Mack Trucks#Maxidyne engine|Maxidyne]], diesel truck engines have increasingly used turbochargers and electronic controls that widen the power band, allowing fewer and fewer gear ratios. As of 2021, fleet operators often use 9, 10, 13, or 18-speed transmissions, but [[automated manual transmission]]s are becoming more common on heavy vehicles, as they can improve efficiency and drivability, reduce the barrier to entry for new drivers, and may improve safety by allowing the driver to concentrate on road conditions. {{Citation needed|reason=This claim needs a reliable source.|date=February 2020}}
===Disadvantages===
 
== Lubrication ==
Many of the disadvantages of a manual transmission involve the driver interaction with the vehicle. While most of these can be overcome with practice and experience, they should be considered:
{{more citations needed section|date=June 2020}}
 
Manual transmissions are lubricated with [[gear oil]] (or [[motor oil|engine oil]] in some vehicles) which must be changed periodically in some vehicles, although not as frequently as the fluid in an automatic transmission. Gear oil has a characteristic aroma because it contains added sulfur-bearing anti-wear compounds. These compounds are used to reduce the high [[sliding friction]] by the [[helical gear]] cut of the teeth (this cut eliminates the characteristic whine of straight-cut [[spur gear]]s). On motorcycles with "wet" clutches (clutch is bathed in engine oil), there is usually nothing separating the lower part of the engine from the [[Transmission (mechanical device)|transmission]], so the same oil lubricates both the [[engine]] and transmission.
* Manual transmissions do not allow the driver to have both hands on the steering wheel at all times.
* Manual transmissions often require the driver to place their full and continuous attention on operating the vehicle, which may be seen as a disadvantage. Many, though, consider this an advantage, as it prevents the driver from other potential distractions like [[mobile phone]] or radio use.
* Inexperienced drivers may place more of their attention on shifting the gears of the transmission, potentially distracting them from the road surroundings.
* A driver may inadvertently shift into the wrong gear with a manual transmission, potentially causing damage to the engine or transmission. It may also result in loss of control due to a sudden change in the vehicle's speed.
* Manual transmissions require a learning curve as one must develop a feel for properly engaging the clutch.
* While it can easily be overcome with experience, manual transmission vehicles require good accelerator pedal application and clutch control when starting the car from a standstill. Excessive RPMs may cause the car to redline, exacerbating engine wear, whereas insufficient RPMs upon clutch release causes the engine to stall due to the lack of momentum required to sustain engine operation.
* The smooth and quick shifts of an automatic transmission are not guaranteed when operating a manual transmission; such changes are dependent on the driver's experience and timing.
* Manual transmissions burden the driver in heavy traffic situations since the driver is seemingly too often operating the clutch pedal. In comparison, automatic transmissions merely require moving the foot from the accelerator pedal to the brake pedal, and vice versa.
* For a person with physical impairment, an automatic transmission might be the only available shifting option. The comparable systems for hand-operated clutch and brakes for a manual-transmission-equipped car are usable only by people with just lower body handicap. Retrofit of such a system also requires extensive modifications to the car.
* Vehicles with manual transmissions are more difficult to start from a rest when positioned upward on a hill as it requires coordination of the accelerator, the clutch pedals, and the handbrake. This can be easily feasible, however, with experience.
* The clutch disc, with the exception of [[kevlar]] clutch discs, wears, and therefore must be replaced periodically. While this is typically a labor intensive process that can be an expensive service, it should not prove more expensive than periodic service to an automatic gearbox in the long run.
 
==Applications and popularity==
Many types of automobiles are equipped with manual transmissions. Small economy cars predominantly feature manual transmissions because they are relatively cheap and efficient, although many are or may be optionally equipped with automatics. Economy cars are also often powered by very small engines, and automatic transmissions can make them comparatively very slow, while a manual transmission makes much more efficient use of the power produced.
 
Sports cars are also often equipped with manual transmissions because they offer more direct driver involvement and better performance. Off-road vehicles and trucks often feature manual transmissions because they allow direct gear selection and are often more rugged than their automatic counterparts.
 
Conversely, manual transmissions are no longer popular in many classes of cars sold in North America and Japan, although they remain dominant in Europe. Nearly all cars are available with an automatic transmission option, and family cars and large trucks sold in the US are predominantly fitted with automatics. In Europe and Asia (except Japan) most cars are sold with manual transmissions. Most luxury cars are only available with an automatic transmission. In situations where automatics and manual transmissions are sold side-by-side, the manual transmission is the ''base'' equipment, and the automatic is optional&mdash;although the automatic is sometimes available at no extra cost. Some cars, such as [[rental car]]s and [[taxicab|taxi]]s, are nearly universally equipped with automatic transmissions in countries such as the US, but the opposite{{dubious}} is true in [[Europe]].
 
In some countries, such as the [[United Kingdom]], [[France]], [[Israel]], [[Ireland]], [[Switzerland]], [[Germany]], [[Austria]], [[The Netherlands]], [[Greece]], [[Sweden]], [[Japan]], [[Belgium]], [[Finland]], [[Singapore]], [[Australia]], the [[United Arab Emirates]] and [[New Zealand]], when a driver takes the licensing road test using an [[automatic transmission]], the resulting license is restricted to the use of automatic transmissions (or clutchless manual vehicles in the case of Australia). This treatment of the manual transmission skill seems to maintain the widespread use of the manual transmission, as many new drivers worry that their restricted license will become an obstacle for them where most cars have manual transmissions, so they make the effort to learn with manual transmissions and obtain full licenses. Some other countries (such as [[Pakistan]]) go even further, whereby the license is granted only when a test is passed on a manual transmission.
 
===Truck transmissions===
Very heavy trucks also feature manual transmissions because they are efficient and, more importantly, can withstand the severe stress encountered in hauling heavy loads.
 
Most companies with fleets of large trucks use 10 speed non-synchronized manual transmissions, because their shift patterns are simpler to learn than the super-10 and 13 speed transmissions. The shift pattern for a standard 10-speed transmission on a truck, such as the Eaton-Fuller RoadRanger 10 speed, is the same as a 5 speed standard in a passenger car. There is a high-low selector switch on the gear shift itself, and after going through 5th gear, which is approximately 15 MPH though it may be geared differently, the switch is flipped up, and the shifter moved back to the first gear position, which is now 6th gear. This causes Reverse to have a HIGH reverse also, which will allow the vehicle to move at speeds up to 25 MPH in reverse, and is definitely not recommended.
 
To start a large truck moving from a standstill, with the engine started and the transmission in neutral, the clutch pedal must be pressed all the way to the floor to engage the clutch brake. The service brakes should also be applied. Once the clutch brake is engaged, the shifter is moved to the low/1st gear, and the clutch and brakes can be released. It is VERY important to note that a heavy-duty truck engine is capable of producing over 1500 foot-pounds of torque and can destroy a clutch fairly easily, so the throttle should not be touched until the clutch pedal is completely released. Giving the vehicle throttle while the clutch is not fully engaged will do nothing more than make the clutch slip, and wont actually help move the vehicle at all, while at the same time overheating the clutch.
 
However, Automated Manual Transmissions (AMTs) and semi-automatic transmissions are becoming more common on heavy vehicles, particularly in the European market. [[Mercedes-Benz]] is one of the manufacturers leading the introduction of AMT and semi-automatic gearboxes. This has been closely followed by other leading truck manufacturers, such as [[MAN AG|MAN]], [[Scania AB|Scania]], [[Volvo Trucks|Volvo]], and [[DAF Trucks|DAF]]. The use of fully automatic gearboxes is more common on buses, with [[Voith]] and [[Allison Transmission|Allison]] being the leading manufacturers of heavy automatic gearboxes, the use of this type of transmission is also common in specialist vehicles, such as fire appliances and municipal vehicles (road-sweepers, refuse collection vehicles, etc.).
 
==Maintenance==
Because clutches use changes in [[friction]] to modulate the transfer of torque between engine and transmission, they are subject to wear in everyday use. A very good clutch, when used by an expert driver, can last hundreds of thousands of [[kilometre]]s (or miles). Weak clutches, abrupt downshifting, inexperienced drivers, and aggressive driving can lead to more frequent repair or replacement.
 
Manual transmissions are lubricated with gear oil or engine oil in some cars, which must be changed periodically in some cars, although not as frequently as the automatic transmission fluid in a vehicle so equipped. (Some manufacturers specify that changing the gear oil is never necessary except after transmission work or to rectify a leak.)
 
Gear oil has a characteristic aroma due to the addition of [[molybdenum disulfide]] compounds. These compounds are used to reduce the high [[sliding friction]] by the [[helical gear]] cut of the teeth (this cut eliminates the characteristic whine of straight cut [[spur gear]]s). Some manufacturers, however, such as [[Honda]], do not use this additive in their gear lube, specifying regular [[motor oil]] until recently, and now their own brand of gear lube which seems to be an enhanced version of [[motor oil]].{{Fact|date=November 2007}} On motorcycles with "wet" clutches (clutch is bathed in engine oil), there is usually nothing separating the lower part of the engine from the transmission, so the same oil lubricates both the engine and transmission.
 
<gallery>
Image:Manual transmission clutch REVERSE.JPG|Reverse
Image:Manual transmission clutch NEUTRAL.JPG|Neutral
Image:Manual transmission clutch GEAR 1.JPG|First gear
Image:Manual transmission clutch GEAR 2.JPG|Second gear
Image:Manual transmission clutch GEAR 3.JPG|Third gear
Image:Manual transmission clutch GEAR 4.JPG|Fourth gear
</gallery>
 
==See also==
{{transmission types}}
* [[Borg-Warner T-56]]
{{Div col|colwidth=23em}}
* [[Toploader Transmission]]
*[[Automatic transmission]]
 
*[[Diesel–electric transmission]]
== Suggested other reading ==
*[[gear ratioFreewheel]]<br>
*[[Gear train]]
[[non-synchronous transmissions]]<br>
*[[Non-synchronous transmission]]
[[transmission (mechanics)]]
*[[Overdrive (mechanics)]]
*[[Preselector gearbox]]
*[[Torque converter]]
*[[Transmission (mechanical device)]]
{{Div col end}}
 
==References==
{{reflist}}
<!--See [[Wikipedia:Footnotes]] for an explanation of how to generate footnotes using the <ref(erences/)> tags-->
<references/>
 
==External links==
{{commons category}}
* {{HSW|page=transmission|name=How Manual Transmissions work}}
* [https://www.nytimes.com/2021/06/24/business/stick-shift-collector-cars.html As Stick Shifts Fade Into Obscurity, Collectors See Opportunity] 24 June 2021 New York Times article by Rob Sass
 
{{Powertrain}}
* [http://www.standardshift.com www.standardshift.com] Manual transmission community site
{{Gears}}
{{Use dmy dates|date=August 2019}}
 
{{DEFAULTSORT:Manual Transmission}}
[[Category:Automotive transmission technologies]]
[[Category:Automobile transmissions]]
 
[[es:Transmisión mecánica]]
[[ja:マニュアルトランスミッション]]
[[ms:Transmisi manual]]
[[pt:transmissão mecânica]]
[[ru:Механическая коробка переключения передач]]
[[yi:הענד ברעיק]]
[[zh:手动变速器]]
Retrieved from "https://en.wikipedia.org/wiki/Manual_transmission"