A transmission service consists of a test drive, removing the transmission pan, draining the fluid (about half of the total), changing the filter and pan gasket, test driving again, and adjusting the linkage and bands if necessary.
The advantages: The filter is changed along with the fluid similar to an engine oil change and the vehicle is test driven and linkage and bands (if applicable) are adjusted. Usually, this service is done at a facility that has more knowledge about transmissions.
The disadvantage: Only a portion of the fluid is changed.
A transmission flush consists of attaching a machine to the transmission and removing virtually all of the fluid and replacing it with new fluid. Unless the pan is removed, the filter cannot be changed. At some facilities, the vehicle is not test driven or the linkage and bands adjusted.
The advantage: A more complete replacement of fluid is done.
The disadvantages: Most of the time this service is done at a facility that has less knowledge about transmissions and none of the additional services are performed.
Occasionally, abnormal operating symptoms arise because the valve body and/or other control items are contaminated by residual wear material that is disturbed and circulated during the flushing process.
