Q&A for How to Clean an Automatic Transmission

The transmission is one of the most expensive parts of your car to repair. Find a reputable shop to give you an estimate on price, then decide if it's more cost effective to do the repair or replace the whole car. As a point of reference, I once paid about $3,000 to rebuild the transmission in a '99 Maxima.

You would have to take the transmission apart to do that. When it doesn't work properly, then usually the torque converter is bad. (The gas mileage goes down and RPMs go up.) This can happen intermittently on the freeway as the torque converter is going bad.

The first thing to do is change the transmission oil. Most cars use a type of oil which has solvent mixed into the oil. As the solvent evaporates, the viscosity increases and the oil becomes too thick. On old cars, adding a transmission additive would work great in many cases. On a CVT Transmission, doing that would void the warranty. You might have a bad transmission.

It depends on the type of filter. Some transmissions use a metal mesh that is not normally cleaned. It is considered self-cleaning as a result of being flushed. Some transmissions use a disposable filter, and once you open the cover on the filter, the filter must be replaced, because the filter surrounding seal will no longer seal properly. That type of filter cannot be cleaned. It must be replaced.

Because the transmission needs to be very clean on the inside for reliability. That's why there is a transmission filter, and sometimes a magnetic retainer for metal particles. A transmission mechanic never wears the type of clothing that might leave lint behind, never wears cotton gloves, etc. The outside is cleaned to help prevent contaminants from getting inside.

Changing the filter will help in maintaining the cleanliness of the fluid. It is responsible for trapping small metal filings or other contaminants from the fluid while it moves through the transmission. On older cars, it is not recommended to change the transmission fluid because the clutch plates etc., have deposits of contaminants and debris on them and have worn into running with them in place. If you change the fluid, you may dislodge these deposits, and your transmission will operate worse than before! Changing fluid is not going to repair a broken or worn transmission parts. You might try adding Lucas Transmission Fix. Drain equal volume of fluid before adding Lucas. It may help.