Automatic Transmission Care
By Peter D. du Pre
According to former Indy car mechanic Dave Bowman, regular fluid and filter changes are the key to keeping your automatic transmission trouble free.
Now employed as a car-care expert for Allied Aftermarket Division (suppliers of Fram, Bendix and Autolite parts), Bowman says that, ideally, the fluid and filter in the transmission should be changed every two years or 24,000 miles, particularly if the vehicle is over five years old. He points out, however, that many newer cars and trucks need scheduled service less often and some new vehicles have transmissions that need no service for the life of the car. He advises that all car owners check their owner’s manual to see what the service interval on their vehicle’s transmission is.
Bowman and other industry experts also warn that by-the-book service may not be adequate if your vehicle is driven hard, tows a trailer, goes off-road, or carries a camper. Under these conditions, changing the fluid and filter every 12 months or 12,000 miles is important because dirt and moisture buildup in the fluid can cause internal damage. Heat buildup can also be a problem. The harder the transmission works, the hotter the fluid gets.
According to Ron Sessions, author of the Turbo Hydra-Matic 350 Handbook (HP Books), the ideal operating temperature for transmission fluid is between 175 and 225 degrees Fahrenheit.
“Anything other than light-duty use will raise fluid temperature beyond this,” says Sessions. “Next to regular fluid and filter changes, installation of an automatic transmission fluid cooler can go a long way towards increasing transmission life, particularly if you tow a trailer.”
Sessions also said that regular fluids checks are very important.
“Checking transmission fluid is a bit different from checking engine oil even though both are checked by a dipstick,” said Sessions. “Engine oil is checked with the engine off, but transmission fluid is checked with the brake set, gear selector in Park, and engine running.”
For an accurate check, the fluid should be at operating temperature and the vehicle should be parked on a level surface. Sessions suggests driving for about 15 minutes to bring the fluid up to temperature before the check. Pull the dipstick out and wipe it clean, then reinsert it. The level should read between the ADD and Full marks. If it isn’t up to level, add fluid via the dipstick tube. To do the job yourself you’ll need a specially designed funnel (available at auto parts stores).
Different vehicles use different types of transmission fluid. The owner’s manual will tell you which type of fluid to use. Pour it slowly into the funnel, checking often to make sure you don’t add too much. Check the fluid at least once a month, topping off if necessary. If you are adding fluid on a regular basis, you’ve got a leak and should get the unit serviced.
Checks and changes of fluid are an important part of transmission care, but so are driving habits. According to Bowman, one common practice that really hurts the transmission is shifting from drive to reverse while the vehicle is still moving. Always make sure your foot is on the brake and the vehicle is stopped before shifting into reverse.
Manual down-shifting into low range can also be damaging. Many vehicles aren't designed for low range driving except under certain conditions. Check your owner’s manual.
Another habit that shortens transmission life is to park without using the parking brake. This is an especially bad practice when the car is parked on a slope since it puts all the vehicle’s weight on a tiny metal catch inside the transmission.