Parts of an Automatic Transmission

by Richard Rowe

By anyone's definition, automatic transmissions are a marvel of engineering. These crucial components have relatively few moving parts, but must function as both a sturdy power-transmitter and hydro-mechanical computer.


The fluid automatic transmission as we know it was first used in 1940 by Cadillac and Oldsmobile, and was a 2-speed called the Hydra-Matic.


The outer case of most automatics is made of aircraft-grade aluminum, and contains all the moving parts and many of the fluid channels required for operation.

Torque Converter

Almost all automatics use a torque (stall) converter. These fluid couplers allow the engine to idle without engaging the transmission.


Automatics contain a separate chamber of labyrinthine fluid channels, one-way check valves, and solenoids known as the valve-body. This unit is widely known as the "brains" of the transmission, and is usually located on the bottom of the case.


Automatics use a fairly small set of "planetary" gears to transfer power, which are located near the back. Planetary gears are widely regarded as the strongest and most space-efficient arrangement available.

About the Author

Richard Rowe has been writing professionally since 2007, specializing in automotive topics. He has worked as a tractor-trailer driver and mechanic, a rigger at a fire engine factory and as a race-car driver and builder. Rowe studied engineering, philosophy and American literature at Central Florida Community College.

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