Why do automatic transmissions fail?

by | Dec 15, 2017 | Automotive


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Automatic transmissions and the brakes on your car fail for the same reason; friction and heat. There are numerous components in an automatic transmission that can and do wear; these include the bands, various bushings, seals, bearings as well as the automatic transmission friction plates. Of all these components, the most critical to proper vehicle operation are the friction plates.

What are the automatic transmission friction plates?

A typical automatic transmission uses anywhere from four to six friction plates, these plates are sandwiched between reaction plates which are made from smooth steel. When the engine is running and the vehicle operator moves the gear selector to reverse or drive, this action opens a valve and hydraulic fluid under extreme pressure moves a piston which compresses all the friction plates and reaction plates tightly together, the result is either forward or reverse motion. As the transmission shifts and o-board computer opens another valve which selects the next gear, this action continues until the vehicle is in top gear.

How wear affects this operation:

Every time the friction plates and reaction plates are squeezed together they wear, the more frequently they are used; the faster the wear is. A vehicle used for city driving where there is a great deal of start and stop driving will invariably have transmission problems long before a car that sees most of its miles put on while driving on highways.

What are the symptoms of wearing automatic transmission friction plates?

As the friction plates wear, you will begin to feel slippage as you go up and down the gears. You can sense slippage; the vehicle does not gain speed as it once did, based on the amount of gas you give it. You will notice the tachometer is showing higher than usual RPMs but your speed is not normal for the condition. This is an indication that the clutch friction lining is wearing off or has worn off.

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