Parts of an Automatic Transmission

Today's automatics are better and more efficient than they ever were

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.

History

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.

Case

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.

Valve-Body

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.

Gear-Set

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.

References

• Procare.com: Transmission Parts
• Edmunds Inside Line: How an Automatic Transmission works
• TCIAuto.com: The Turbo 400 Transmission

Resources

• Planetary Gearset Animation (Video)