Types of Transmission Shafts

by LaTasha Favors

Transmission shafts can be found in a manual transmission gearbox. The purpose of a transmission gearbox is to transfer the high output of an automobile's engine to the wheels, and in the process reduce it to a compatible speed. The gearbox does this through a complex arrangement of gears and shafts.

Input Shaft

The automobile's engine crankshaft turns and creates power. This mechanical energy must first go through the transmission gearbox before it eventually reaches the wheels. The first component to receive this energy is the input shaft. It can be engaged or disengaged through the mechanism of the clutch. Typically in a rear-wheel drive car, the input shaft is designed to lay along the same line as the output shaft, forming what seems like a singular component that is sometimes called a main shaft.

Counter Shaft

The counter shaft lies parallel to the main shaft and is driven by the input shaft through a pinion gear. In a basic manual transmission design, the transmission gears are attached to the counter shaft permanently, spinning along with it. In front-wheel-drive cars, the input and counter shafts are actually the same thing. It bears the clutch mechanism, which connects it to the engine and transfers power to the output shaft through the gears that lie along it. Sometimes the counter shaft is also called a lay shaft.

Output Shaft

The final component that carries the power out of the transmission gearbox and on to the wheels is the output shaft. A set of transmission gears parallel to those on the counter shaft are arranged along the output shaft; it is driven by the counter shaft through these gears. Both output and counter shaft gears are usually already meshed but the output shaft gears are not permanently attached to it. These gears are the ones actually shifted manually by the driver. Only the one gear selected is fastened and rotates the output shaft along with it, while the others spin freely until another one is selected.

Other Configurations

A design that uses the sequential gearbox---where the stick is moved up or down---adds another shaft in the transmission called the selector shaft. This shaft turns by certain degrees with every shift and moves the collars that fasten a shifting gear on the output shaft. Meanwhile, the dual-clutch type of configuration actually makes use of two output shafts where the shifting gears are distributed.

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