How to check the transmission

Updated: August 27, 2013

Automatic transmission

Automatic transmission
Automatic transmission cut in half.
Click for larger view

An automatic transmission becomes more reliable these days, but still it's a most-easy-to-break and very-expensive-to-fix part of the vehicle. If heavily abused, the automatic transmission can be easily destroyed within just half an hour. For example, a friend of mine had burnt the automatic transmission up in 20 minutes when he was trying to free his shiny Audi from the snow in the next day after he bought it! It cost him about $2000 to rebuild it and after one year it broke down again. Also, an automatic transmission is very sensitive to the transmission fluid quality and condition. Improper fluid type can damage the transmission. A person I know added gear oil (oil for manual transmission) into the automatic transmission. Guess what, 30 minutes of driving was enough to kill the transmission. Obviously, when buying a used car, the automatic transmission is one of the most important parts to check. In this article I described few signs that may indicate potential transmission problem in a used car. In addition, I strongly recommend to have the used car inspected by a mechanic before buying it, it will well worth it.
Ask the previous owner or salesperson if any repair has been done to the transmission. If the automatic transmission has already been rebuilt, it's probably better to avoid buying such a car. It's not like all rebuilt transmission will have problems - some of them will work even better than before. The problem is that not all transmission shops can do equally good job. And since there is no way to verify if it was rebuilt properly or not, it's better not to take chances. Another thing to be concern about, ask if the car was used for towing a trailer; towing a trailer adds extra load on the transmission and it wears faster. Watch out for the trailer hitch.

How to check the automatic transmission

Transmission fluid
Automatic transmission fluid

First, check the transmission fluid level and condition. If you don't know how to do it, here is an illustration:
How to check the automatic fluid
With the engine idling and transmission in "Park" (some car may have different procedure, refer to the owner's manual) remove the automatic transmission dipstick and wipe it out with the clean lint-free cloth. Insert the dipstick back fully and then pull it out again. Check the fluid level; low level may indicate a transmission leak. Look at the fluid very closely. It helps if you drip the fluid onto a white paper to be able to see the fluid condition. The transmission fluid should be clean and transparent, without any metal filings or black flakes. The new fluid usually comes red. Over the time, it become more brownish, but it shouldn't be very dirty or black. Look at the image. Try to smell the transmission fluid; It should not have a burnt smell.
All this may seem difficult, but when you check few similar cars, you'll be able to see the difference. If the transmission fluid is too dirty or black, or smells burnt, it's better to avoid such a car.
Keep in mind, however, that some modern cars don't have the transmission dipstick and require special procedure performed in the auto repair shop to check the fluid level. In this case, the only way to check the transmission is the test drive. Read about it on the next page.