How to check transmission and discover possible transmission problem when buying a used car.

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 a 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.

At the beginning

First, check the used car history records; it may save you some time and money. If the used car history report shows that the car you want to buy was used as a rental vehicle or has been involved in an accident, there is no point to even look at it. Follow this link to find out How to check a used car history
Ask the previous owner or salesperson if any repair has been done to the transmission. If the automatic transmission is already rebuilt, try to avoid buying such a car. It's not like all rebuilt transmission will have problems - some of them work even better than before. The problem is that not all transmission shops can do equally the same high-quality 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 you are looking for was used for towing a trailer. I've seen the transmission worn out in many cars that were used for towing a trailer.

How to check an automatic transmission

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, transmission in "Park" (some car may have different procedure, refer to owner's manual) remove the automatic transmission dipstick and wipe it out with the clean cloth. Then insert it back and pull out again. Check the fluid level, low level may indicate a transmission leak. Look at the fluid very closely. It helps to drip the fluid on a white paper to be able to see fluid condition. The fluid on the paper should be clean and transparent, without any metal filings or black flakes. New fluid usually comes red. Over the time and use it become more brownish, but it shouldn't be black. Look at the image on the left.
Try to smell the fluid. It should not have a burnt smell.
All this may seem to be difficult for you, but when you check few similar cars, you'll be able to see the difference.
If you discover that transmission fluid is too dirty or black, or smells burnt, avoid buying such a car.
Keep in mind, however, that some modern cars simply don't have the transmission dipstick and require special procedure performed in a garage to check the fluid level. In this case, the only way to check it is a test drive.

Automatic transmission test drive

One of the indications of a transmission problem is delayed engagement, when there is a long delay between the moment you shift the shifter into "D" (Drive) or "R" (Reverse) and the moment the transmission kicks in.
It's easier to note delayed engagement after a car was sitting for a while: With the transmission in "P" (Park) start the engine, and wait until the engine rpm has reduced to normal level (650 - 850 rpm).
With your foot holding down the brake pedal, shift to the "D" (Drive) position. Almost immediately the transmission should engage - it feels like the car wants to creep forward. This should happen very smoothly, without a strong jerk or clunk.
Shift to "N" (Neutral), and the transmission should disengage. Now, still holding the brakes, shift to the "R" (Reverse) position. Again, the transmission kicks in almost immediately - you will feel the car wants to creep backward. This also should be very smooth, without a jerk or clunk.
Now, still holding the brake pedal down, try to shift from D to R and back. There should be no strong jerk or clunk.
If there is a notable long delay (more than 1 seconds) between the moment you shift and the moment the transmission kicks in, such a transmission might be either too worn or has some problem, avoid this car.
If you feel a strong jerk or clunk while shifting, the car may have a transmission problem, avoid such a car.

Now it's time to test drive the car.
With the shifter in "D" (Drive) position drive gently, with smooth and gradual acceleration. Until the vehicle reaches a speed of 30-37 mph (50-60 km/h) or you should feel the gears shifting at least twice (from first to second, and from second to third gear).
All shifts should be done very smoothly, without jerks or slipping.
You should be able to feel when the transmission shifts by the slight change in the engine tone or change in engine rpm. If the transmission is extremely worn it may shift with quite a strong jerk, shudder or a delay (especially from first to second gear).
Driving at a speed of 25-30 mph (40-50 km/h) if you press down the accelerator pedal for a few seconds, you should feel downshifting to the lower gear, if the automatic transmission works properly.
The next step: check overdrive.
While driving at 60-70 km/h or 35-45 mph on a level road, without using the accelerator, switch overdrive ON. You should feel an upshifting to the next speed. Switch it to "OFF," and you should feel a downshifting.
Another thing that may indicate the transmission problem is the slipping. When the transmission is excessively worn it may slip - which means you press the accelerator, the engine rpm increases but the speed remains the same.

If during the drive test you feel any problem such as transmission seems to slipping or shifts with a jerk or shudder or if the transmission got stuck in some gear, or has trouble shifting into a particular gear (for example, from second to third), avoid buying such a car.
Test-drive the car as long as possible. Often the transmission may work well when it's cold but when it's warmed up it starts giving troubles or visa versa. So, it's better to spend more time checking the transmission than later fixing it endlessly. Normally there should be no shudder, no noises or any kind of strong jerks at any speed and at any engine temperatures while any shifting. If the salesperson tells you that the jerks or shudder or any other abnormal transmission behavior is "normal" for this car or it's just because the car is cold or anything alike, don't trust them. If the "check engine" and/or a flashing overdrive light comes on while driving, have the problem assessed with your mechanic before buying a car.

How to check manual transmission

First, check for oil leaks. There should be no leaks.

Manual transmission test drive:

Now, (with caution - safety first!), shift the transmission lever into neutral. Apply the parking brake. With the engine idling, press the clutch pedal all the way, hold it down, and listen for noises. Then release the pedal and listen for noises again. There should be no loud noises at either positions.
The next step is the test drive.
Try to drive the vehicle at different speeds in all gears, one by one. Every gear should shift smoothly and easily without any noises or jerks. While driving at the second or third gear, try to press down sharply on the accelerator pedal for an instance. The clutch should not slip.
If you feel any slipping (e.g. the engine rpm increases but the speed remains the same), the clutch most likely has to be replaced.
Try to drive with acceleration and deceleration - there should be no grinding, whining or humming noise under any condition. All the gears should shift easily and noiselessly.

Check the CV joints

Broken CV joint boot

A Constant Velocity joint or CV joint is an important component of the drive train. The CV joint is packed with grease and protected by the rubber or plastic boot. Most common problem with the CV joints is when the protective boot gets damaged. Once this happens, the grease comes out and the moisture and dirt come in, eventually causing the CV joint to fail due to lack of lubrication and corrosion. In worst case, the CV joint may disjoin causing the vehicle to stop running. You can check the condition of the CV joint boots visually. You can see them with the front wheel turned outside, looking down from the front of a car. None of them should be damaged. Look at the photos. The CV-joint boot in upper image is damaged, in the lower image it looks OK. If a boot is damaged, it has to be replaced as soon as possible. If continue driving with broken boot, the CV joint or a whole drive shaft will need to be replaced. While drive test, If you hear clicking or popping noise when turning, the CV joint is probably already defective.

CV joint boot is OK

Have the car inspected by a mechanic

Before making your final decision, have the car inspected by a mechanic of your choice. There are many things that only an experienced mechanic will be able to reveal.

If you are looking for more detailed technical information

If you want to find more technical information about you car such as all kind of diagrams (transmission diagram, engine diagrams, vacuum line diagram, electrical diagram, etc.) repair information, specification, fluids type, maintenance schedule, component location, service bulletins and so on, there is a website which for a small fee allows you to browse all such an information for almost any car model on-line. To learn more visit this page:
Where to find technical information about your car