Sunday, December 17

How To Service Your Car's Automatic Transmission

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Automatic transmission repairs are expensive. Unlike manual, transmissions, automatic transmissions are sensitive mechanisms and easily damaged. The best way to protect your transmission is by performing regular fluid and filter changes.

30,000 miles –Vs- 100,000 Mile Servicing

For many years, auto manufacturers have been recommending changing the automatic transmission fluid and the transmission’s fluid filter every 100,000 miles. Recently, they have started going back to recommending this service every 30,000 miles. Servicing an automatic transmission every 30,000 miles is more realistic. It is the best way to protect your car’s transmission from serious problems. Depending on your driving habits, you might consider performing this service every twelve months.

Keep A close Eye On Fluid Condition

You need to look at more than the position of the ATF on the dipstick when you do your weekly check. You need to take a close look at its color and note its smell. Viable transmission fluid is a bright red color and has a sweet smell. You need to change transmission fluid that is dark or smoky in color with a burned smell to it. You do not want to wait until the transmission fluid has reached this stage. Change the fluid and filter once a year whether they need it or not. Servicing your car’s automatic transmission is a terrific way to learn more about how your car works.

Tools And Supplies You Will Need

A service manual for your car
Automatic transmission fluid
Transmission fluid filter kit
Service ramps or 
Garage floor jack and jack stands
Wheel chocks
Fluid drain pan
3/8 inch drive socket set with metric and SAE sockets
3/8 inch drive “Click” torque wrench
Flare nut wrench sets (metric and SAE)
Mechanic’s gloves
Safety goggles
Shop towels/rags

Raise The Car

Raise the car, with the garage floor jack and place the jack stands under safe jacking points for support. Never crawl under a car supported by a jack. If you are using a garage floor jack and jack stands for the first time, read my article Hydraulic Floor Jacks and Jack Stands: Essential Garage Equipment For DIY Auto Mechanic before proceeding to the next section of this article. This article contains valuable information for your safety.

No Drain Plug In The Torque Converter

Unlike older cars, modern cars do not have a drain plug in the torque converter. With older cars, we could drain the fluid from the torque converter but that is not possible with newer cars. Dropping the transmission’s oil pan is not enough to get all of the old fluid out because of what remains in the torque converter housing. To get all the fluid out we will use the transmission built in pump to pump it out before dropping the transmission’s oil pan.

Check Your Service Manual

Check your service manual to discover which oil cooler line is bringing fluid from the transmission to the oil cooler inlet. Disconnect inlet line using the flare nut wrenches. Attach a short piece of hose to the line and place the other end of the hose in the drain pan. Have a helper start the car while you watch the oil entering the drain pan. When air bubbles start to appear in the oil shut the engine off and reconnect the oil cooler line. You have removed the majority of the transmission fluid and are ready to remove the transmission’s oil pan.

Remove The Oil Pan And Filter

Remove the studs holding the oil pan in place. Clean the pan using a high quality auto parts cleaner. Remove the fluid filter following the instructions in your service manual or the instruction sheet that came with the replacement kit. Carefully scrape any of the old gaskets off the transmissions flange.

Install The New Filter

Install the new fluid filter, pan gasket, and pan. Fingers tighten all the bolts and then torque them to the specified number of inch-pounds using the torque pattern shown in the service manual. Do not over tighten. Pour in the correct number of pints of new fluid as specified in the service manual.

Check For Leaks

Start the engine and let it idle. Check the oil pan and cooler lines for leak. After the fluid has reached operating temperature, check the fluid level one last time.


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