How Vehicle Gearboxes Work – M & T Transmissions

Gearboxes - The Basics

What Is A Gearbox?

a hand drawn illustration of a typical vehicle gearbox with the side casing removed shoing all the gears and shafts

A Gearbox is typically enclosed in a aluminium alloy casing a collection of connecting shafts and gears submersed in oil for lubrication and cooling.

What Does A Gearbox Do?

Facilitates the varying of torque and speed on the box output shaft with reference to the input shaft. See our superb manual vehicle gearbox animation to see a gearbox in action.

Everything Your Gearbox Does
  • Varies the torque on the output shaft
  • Varies the speed of the output shaft
  • Provides a reverse gear
  • Disconnects and connects drive between the clutch and the differential
  • Provides an overdrive gear which rotates the output shaft more per turn than the input shaft, usually for fuel economy

Gearbox Shafts

Input Shaft

1 shaft with 1 gear

The gearbox input shaft is considerably shorter than the output shaft and fixed to its gear. It is responsible for transferring drive from the vehicle engine assuming engaged through the clutch system into the gearbox. Here its gear drives the connecting layshaft gear and thus drives the layshaft. There is no selector here and as such the input shaft permanently drives the layshaft. Pressing the drivers clutch pedal disconnects drive from the input shaft and consequently the layshaft.

Lay Shaft

layshaft with 5 various size gears

The lay shaft is fixed to its gears and is driven at a constant speed by the engine regardless of the gear the gearbox is in including reverse or neutral. The clutch (operated by the drivers foot pedal) enables the lay shaft speed to be independent of the engine by utilising a friction taper or similar to press up against a gear to make the gear rotate at the same speed forcing the lay shaft to change accordingly.

Output Shaft

mainshaft with 4 various size gears

The output shaft is not fixed to its gears. The gearbox output shaft is a simple splined shaft that is connected to its gears only via the dog clutches, as the gears themselves are not splined. 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.

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