What's The Difference Between A Flush And A Transmission Service?

First of all, lets take a look at what is done when you perform routine maintenance on an automatic transmission. You start by getting the history on the transmission from the owner and then test drive the car or truck to see how the transmission performs. The next step is to check the transmission for leaks and remove the sump pan, draining 4 to 6 quarts of fluid. This can't be done with all transmissions since some are designed without a pan. The technician then examines the contents of the pan and filter paying close attention to any unusual material that may have worn off internal parts. The pan is cleaned, filter and gasket replaced and pan is reinstalled. New fluid is added to the full mark and the vehicle taken on another test drive to insure its proper operation.

There are two significant differences between a transmission service (routine maintenance) and a flush (also called a fluid exchange). The first is during a service, approximately 40-45% (4 to 6 quarts) of the transmission's fluid is changed and a flush changes closer to 100%. The second difference is a "pan drop service" allows a tech to view any debris that may have worn off the internal parts of the transmission and with the flush procedure, the pan is not removed. The fluid is flushed by disconnecting the transmission's cooling lines at the radiator. A third difference is that the flush does not allow for the filter to be replaced.

There is an alternative to the two procedures described above and it is called the "total flush" which combines the best of both. In this instance, once the pan and filter have been removed, an adapter is inserted where the filter normally is located and 2 to 4 gallons of new fluid flushes the old fluid back to where it would normally flow into the pan. Since the pan has been removed for this procedure, the dirty fluid "rains" down into a large catch basin and discarded. Once the fluid has been completely flushed, a new filter and pan gasket are installed along with the transmission's pan which has been cleaned. The transmission is topped off with more new fluid and taken for its second test drive to insure it works perfect.