To keep your automatic transmission in good working order and prevent costly repairs it is important to change the automatic transmission fluid (ATF) periodically. However, in many transmissions, there is no drain plug on the torque converter, which holds much of the fluid, so it cannot be completely drained to remove all the old fluid. This is all the more reason to change the fluid frequently as well as replace filters and cleaning screens.

There are a couple of ways to replace all the ATF without disassembling the transmission. Probably the best way is to use a fluid flushing machine which replaces all the ATF. A good transmission shop should have such a machine. You should definitely flush the transmission if you are switching from a petroleum-based ATF to a synthetic ATF. While the two types of fluid are compatible, pure synthetic ATF, which costs more, will provide the maximum benefit.

Amsoil Inc., one of the largest marketers of synthetic oil, ATF and other products, offers a technique for removing virtually all the old ATF from the transmission. First, service the pan as normal while changing the filter. If the transmission is equipped with a rubber-on-steel gasket, carefully clean and reuse the gasket. Otherwise install a new gasket, if one is used. Fill the pan with fresh fluid, but do not start the engine yet.

Disconnect a transmission cooler line at the radiator, screw an adapter into the radiator side and slip a piece of tubing on both open lines and run both tubes into a collection bottle. Have a helper crank the engine over and stay in the drivers seat. If you have raised the vehicle off the ground, make sure you use jackstands. Leave transmission in park. On some Chrysler products, you will have to put the transmission in neutral. Fluid will be pumped out one of the two pieces of tubing from the torque converter. Fill the transmission as the fluid is being pumped out. When you get all the old fluid out you will notice a change in tint as new fluid replaces the old stuff.

Check your owner’s manual to determine the amount of ATF the transmission holds as another indication when all fluid has been replaced. Shut the engine off immediately, reconnect the system properly, run, test drive and verify proper fill level.