In Reply to: Transmission fluid change, How important? posted by MiKe on January 25, 2000 at 18:09:51:
While it is true that gearbox oil does not see conditions anything like that experienced by engine oil (combustion byproducts, moisture condensation, carbon, etc.) it is still necessary to replace it periodically.
Gearbox oils contain friction modifiers that allow good synchro action as well as lubricants that ensure protection of the gears. For example, the oil has to have a certain amount of "cling" that maintains an adequate oil film on vertical surfaces.
These do eventually lose some of their properties and the oil should be replaced. Besides, if nothing else, small metal particles that may be in suspension will get drained out.
Check whether your tranny uses ATF or not. There should be a sticker on the bellhousing that clearly indicates the type. Based on that, use a good quality synthetic like Redline or other of your choice.
Have you replaced your differential oil per the recommended interval? Similar logic applies there.