Manual transmission

A manual transmission (MT), also known as manual gearbox, standard transmission (in Canada, the United Kingdom and the United States), or stick shift (in the United States), is a multi-speed motor vehicle 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).

However, sequential manual transmissions, which are commonly used in motorcycles and racing cars, only allow the driver to select the next-higher or next-lower gear.

Operating such transmissions often uses the same pattern of shifter movement with a single or multiple switches to engage the next sequence of gears.

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".

Six-speed manual transmissions started to emerge in high-performance vehicles in the early 1990s, such as the 1990 BMW 850i and the 1992 Ferrari 456.

[15] 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 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.

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.

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.

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.

[citation needed] The synchromesh system must also prevent the collar from bridging the locking rings while the speeds are still being synchronized.

The latter involves stamping the piece out of a sheet metal strip and then machining to obtain the exact shape required.

Larger differences in speed between the input shaft and the gear require higher friction forces from the synchromesh components, potentially increasing their wear rate.

[20] Most transmissions include a lockout mechanism to prevent reverse gear from being accidentally selected while the car is moving forwards.

The movement of the gear stick is transferred (via solid linkages or cables) to the selector forks within the transmission.

Motorcycles typically employ sequential manual transmissions, although the shift pattern is modified slightly for safety reasons.

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.

Most FR (front-engined, rear-wheel drive) vehicles have a transmission that sits between the driver and the front passenger seat.

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 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.

All Toyota Crown and Nissan Cedric 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,[vague] a 5-speed column shifter has been offered in some vans sold in Asia and Europe, such as Toyota Hiace, Mitsubishi L400 and the first-gen Fiat Ducato.

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.

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.

[25] 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.

Diesel truck engines from the 1970s and earlier tend to have a narrow power band, so they need many close-spaced gears.