How a Four-Speed Gearbox Works

Gearbox Basics

A manual transmission, or stick shift, has two main external parts: a gearbox and a clutch. It uses the gearbox to switch between gears. Most vehicles have four or five gears (and reverse), but they can come with as few as two and as many as eight.

How It Works

The gearbox is used to both increase the torque (in the input shaft) and decrease the speed of an output shaft. This causes the output shaft to rotate more slowly than its input shaft, further increasing the torque. This process happens in automatic transmissions too, but the driver controls the torque more directly in a manual-transmission car.

Layout

While a five-speed gearbox has several different possible layouts, most four-speed gearboxes use the same basic configuration. The main shaft is set at neutral. Pairs of first-second gears and third-fourth gears lie along the neutral shaft. This makes it easy for the driver to shift among all of the consecutive gears except for second and third, and is the most natural configuration for a four-speed gearbox. The reverse gear is the one aspect of the gearbox configuration that varies with different gearboxes. It is usually located in one corner, but may be in the upper left, upper right, lower left or lower right, depending on the vehicle.