How to Fix a Slipping Transmission

Unless you're a mechanic, you probably can't fix a slipping transmission on your own. A transmission can slip for several reasons: the fluid could be low, the clutch could be worn out or broken, the torque converter could be bad or a computer chip is acting up. Only one of these problems is easily fixed by car owners.

Transmission Troubles and Fixes

• Low fluid: If you notice the transmission starting to slip, especially in reverse, check the transmission fluid, which may be low. Most automatic transmissions have a dipstick in the engine compartment. Check the level of the transmission fluid while the vehicle is running and in park. If your vehicle is an automatic and does not have a dipstick, or if it is a standard shift, there is a plug on the transmission pan. Put a drip pan under the plug and remove the plug. If the transmission fluid, or gear oil in standard-transmission vehicles, is level with the bottom of the hole, you have enough transmission fluid and the cause for slippage is not low fluid. If fluid is the cause, simply add enough to bring it level with the bottom of the hole or up to the recommended level on the dipstick. 
• Leaking: If you find yourself replacing transmission fluid frequently, it's time to find the source of the leak. Check the seal at the front of the transmission, where it meets the engine. A fluid leak here indicates a front seal that should be replaced. On front-wheel-drive vehicles, check the seals on either side, where the axle travels through the transmission. For rear-wheel-drive vehicles, inspect the seal at the back of the transmission. Replacing the rear seal on a rear-wheel drive transmission is the least expensive of these repairs. Seal repairs on front-wheel-drive vehicles are costly because the axle must be removed. Front seals are always expensive to replace, because the entire transmission must be removed from the car. If you have this done, it's a good idea to replace all the seals and possibly the clutch, since you'll be spending a lot just to have the transmission taken out.
• Bad torque converter: If fluid levels are normal, listen for a tinkling noise when you try to move the vehicle. If you hear it, chances are, the torque converter is broken or worn out.
• Clutches: If the fluid level is good and you don't hear noises, bad clutches are the most likely problem. If enough material is worn off the clutches, they will not stick to each other, allowing the gears to slip.
• Gears: It is extremely rare for the gears in a transmission to go bad, but you'll know it if they do. The transmission may slip when you change gears, then lock into gear suddenly with a clunking sound. You'll need to have the transmission rebuilt or replaced if this happens.
• Computer chips: Faulty computer chips can cause a variety of problems in transmissions, from slippage to a failure to engage some or all of the gears. You won't be able to diagnose this problem yourself; instead, you'll need to visit the dealer or a specialty shop, such as AAMCO or Mr. Transmission, and have the car connected to a computer. Computer repairs seldom require the transmission to be removed or replaced, but chip and sensor replacement can run from $500 to more than $1,000, depending on the parts needed and their location.