Maintaining your transmission

Automatic transmission
Automatic transmission. Click for larger view

An automatic transmission is the most complex and one of the most expensive to repair components of your vehicle. It has to do a lot of work and it doesn't require as many regular services as your engine.

This is one of the reasons the transmission often gets neglected. Everybody knows that engine oil must be changed regularly for the engine to last, but what about the transmission?

An automatic transmission depends on the transmission fluid to do all the work: the transmission fluid transfers the hydraulic pressure to shift the gears, it lubricates all the moving parts and cools down the transmission. The transmission fluid lasts longer than engine oil, but it still deteriorates over time and under load and high temperature. For this reason, keeping your transmission fluid clean and at the proper level is vital. It's also important to use only the proper type of the transmission fluid.

Where is the automatic transmission dipstick located

Check the owner's manual to see where the transmission fluid dipstick is located in your car. You can quickly find in the book's maintenance section:
Maintenance » Do-It-Yourself Maintenance » Engine Compartment.
Yo will see the engine compartment map with the descriptions. If you don't have the owner's manual, here is the link where to download it: car owner's manual. Here are few examples: click on the car model to see where is the transmission dipstick located in that car (pointed with orange arrow).

1998 Toyota Corolla
2012 Toyota Corolla
2007 Dodge Ram
2000 Ford Focus
2006 Toyota Camry
2007 Honda Accord
2007 Jeep Wrangler unlimited
2006 Ford Escape
2006 Dodge Caravan
2006 Mazda 3

Checking automatic transmission fluid

On most cars and trucks, you still can check the transmission fluid level and condition with a dipstick, similarly to an engine oil. Check your owner's manual for the correct procedure, as it may be a bit different for different cars; for example, in many Honda vehicles the transmission level is checked with the engine off, while it most other cars, the transmission fluid level is checked with the engine running and the transmission in Park. Some newer cars and trucks actually don't even have a transmission fluid dipstick and the level can only be checked at the dealer or a repair shop.

Transmission fluid dipstick

In this Mazda 6, for example, according to the owner's manual, the steps are as follows:

1. Park on a level surface and set the parking brake firmly.
2. Idle the engine about two minutes. Push down on the brake pedal.
3. Move the shift lever through all ranges and set it at P.
Checking transmission fluid level

4. With the engine still idling, pull out the dipstick, wipe it clean, and put it back.
Transmission fluid level

5. Pull it out again and check the fluid level.
The proper fluid level is marked on the dipstick.

This is how it looks. In this photo, the level is OK and transmission fluid still looks not too bad, but it won't be a bad idea to change it in the near future.
Checking automatic transmission fluid condition

To see the condition of the fluid better, drip it on a white paper towel. The new automatic transmission fluid usually comes red. Over time, it deteriorates and becomes more brownish. It's a good idea to change it before it becomes too dark. See the chart.

Transmission fluid color

The transmission fluid change intervals vary from 25,000-30,000 miles to 60,000 miles. You can find the exact interval in the maintenance schedule in your owner's manual or just call your dealer.

What can damage your automatic transmission

Most of the transmission problems starts from overheating. Under heavy load, such as when towing a heavy trailer, rocking the vehicle from the snow, having continuous stop and go traffic in hot weather, racing, etc. the transmission overheats. At higher temperatures the transmission oxidizes, losing its lubricating qualities and leaving deposits all over inside the transmission. If you'd check the automatic transmission fluid in an overheated transmission, it would be dark and dirty, with a strong burnt smell. Exposed to the heat the rubber seals, O-rings become hard and brittle. The metal parts warp causing valves to stick in. All this, sooner or later, results in transmission failure. For example, a friend of mine has burned his automatic transmission when he was spinning the wheels too hard trying to free his shiny Audi from the snow; it was on the next day after he bought it!

However, overheating is not the only reason; sometimes an automatic transmission problems are caused by design flaws faulty parts, lack of maintenance or poor rebuilt job. A too low or even too high transmission fluid level or wrong transmission fluid type can also cause transmission problems. A person I know added a gear oil into the automatic transmission by mistake - guess what happen - the transmission failed after 40 minutes of driving!

How to prevent automatic transmission problems

Regularly check your parking space for leaks and if you see any, get it fixed before lack of oil or fluid can cause expensive problems.
Once in a while check the transmission fluid level and condition. However, not all cars have the automatic transmission dipstick; in some cars, for example, in late Volkswagen models, the transmission fluid can only be checked by a mechanic in the repair shop. You can check your owner's manual for instructions to check the automatic transmission fluid. If the transmission fluid level is too low, there is a leak somewhere that needs to be fixed. Change the transmission fluid as often as it's recommended in your owner's manual or when it becomes too dark (rather brown than red) or dirty.

Use only the same type of transmission fluid as specified in the owner's manual or on the dipstick. Many newer vehicles are very sensitive to the fluid type. For example, the owner's manual for 2008 Honda Civic says "Using transmission fluid other than Honda Genuine ATF-Z1 may cause deterioration in transmission operation and durability, and could result in damage to the transmission". Never shift to the Reverse or Park modes until the car comes to a complete stop. Don't shift the transmission from 'Park' to other modes at high engine RPMs.

In many cars, the automatic transmission can be damaged if towing with the drive wheels on the road. If you have to tow your vehicle, check your owner's manual for the proper way of doing it. If you planning to tow a heavy trailer with your vehicle, consider installing an additional transmission fluid cooler. It's also good idea to change your transmission fluid more often when towing a trailer.

Transmission flush vs drain and refill

There are two ways to replace transmission fluid. The drain and refill method involves draining transmission fluid from the drain plug, or if there is no drain plug, from the transmission pan and refilling the transmission with new fluid. In some cars, there is a transmission fluid filter that also should be replaced when the fluid is changed.

The transmission flush is done with a special transmission flush machine that is connected in series to one of the transmission fluid cooler lines. With the engine running the transmission flush machine gradually pumps out old transmission fluid replacing it with new fluid at the same time. What is the difference? With the 'drain and refill' method only about 40%-50% of transmission fluid can be changed at once, because a large portion of fluid remaining in the torque converter, valve body and other parts of the transmission cannot be drained. Using the transmission flush machine allows replacing around 90-95% of transmission fluid at once.

Which method is better? Opinions are divided. Using a transmission flush machine is obviously quicker and more efficient method and it is successfully used in many auto repair shops. However, half of the mechanics you ask, will tell you that it's better to repeat a 'drain and refill' method a few times. Some car manufacturers even don't recommend using transmission flush machines on their cars. For example, Honda mentioned in one of the newsletters for Honda technicians that "Transmission flush systems are not approved or recommended for Honda A/Ts".

All in all, the transmission flush method, if approved by a car manufacturer, might work well for low-mileage cars, while the 'drain and refill' method is safer for high-mileage vehicles. With either method, only the recommended transmission fluid type should be used.

How to use an overdrive

Generally speaking, an overdrive (O/D) is the highest gear in the transmission. On most cars the automatic transmission has three or four gears and an overdrive (forth or fifth gear). Overdrive allows the engine to have less rpm with the higher speed in order to have better fuel efficiency. When you switch it on, you allow the transmission to shift into overdrive mode after the certain speed is reached (usually 30 - 40 mph depending on the load). When it's off, the transmission won't shift into the overdrive gear. In normal driving condition the overdrive should be always on.
You may need to switch it off when driving in mountainous area or towing a trailer.
The automatic transmission automatically shifts from O/D to the lower gear when it feels more load. When it feels less load it shifts back to the O/D. Sometimes, under certain conditions, e.g. when driving uphill or towing a trailer, the transmission may not be able to decide to stay in OD or to shift into lower gear and it starts to shift back and forth continuously. This is the time you may want to witch the overdrive off and help the transmission to decide.
You also may need to switch it off when you want to slowdown using the engine braking, for example, driving downhill. For more details how to use an overdrive, check your owner's manual.

When it's time to visit a transmission shop

If you experience any problems with your transmission such as leaks, noises, problems with shifting, etc. Don't wait until the problem becomes worse and car will finally stop moving somewhere on a highway; visit your trusted local transmission shop. The automatic transmission problems never disappear by themselves. Also, when going for the repair, try to explain to service person in more details: what exactly problem you experience, when it happens, what does it look like. It will be easier for them to repair the transmission. Before going to the transmission shop for the repair ask them about the warranty - the longer warranty they will give you, the better will be the repair.
You might also be interested: