What Is the Purpose of a Car Transmission?

by Joanne Robitaille
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vintage car chrome engine image by Leticia Wilson from Fotolia.com

Transmissions are an essential part of what makes a car run. It's attached to the engine and ensures that the engine and wheels turn in sync with each another. Think of the transmission like a chain on a bicycle. It keeps the engine (pedal) turning in time with the wheel regardless of what gear the vehicle's in. It's also the part that you don't think about until it stops working.


A transmission is the part of an engine assembly that connects the engine to the wheels. It's within this piece of machinery that the power produced by the engine is transferred into the wheels. A level of precision is needed while doing this because each engine operates at its own optimum RPM (revolutions per minute) range and it's the transmission that keeps everything in balance.

Front vs. Rear Wheel Drive

The location and design of a car's transmission differs depending on whether the car is front or rear wheel drive. For a car that operates in rear wheel drive, the transmission will extend from the back of the engine toward the rear wheels (the hump between the driver and passenger seats is usually where it's located). The transmission connects to the drive shaft that is hooked up to the rear axle. The transmission for front wheel drive cars is called a transaxle and it hooks around the engine on the driver's side and is directly attached to the front axle.

Planetary Gear Set

Within the transmission, the planetary gear set allows the gears to shift both forward and reverse. The main component of this is a large gear ring that has four smaller gears inside. These smaller gears are configured much the same way that our solar system is: a central larger gear with two or more smaller ones orbiting it. This gear system in configuration with the input and output shafts are what allows engines to switch gears in a manual transmission vehicle.

Torque Converter

The torque converter is the part of an automatic transmission that allows an engine to keep running even while the car isn't in motion. It's made up of three parts: the pump, the turbine and the stator. When an engine's in motion, transmission fluid is forced from the pump to the turbine and then into the stator. If the force of the fluid entering the turbine slows (as it would when a car has stopped), the stator is locked until turbine speed picks back up.

Computer Sensors

Computers are now a part of every car transmission. Sensors within the transmission monitor everything from vehicle speed to engine load and pedal position and use that information in order to manage the gear shifting process. More advanced transmission computers even allow for an instantaneous switch between automatic and manual control of the transmission.

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