Originally Posted by Kestas
Every time I query the masses, the common belief is that transmission fluid is indeed filled-for-life. This is an uphill battle for us to educate the public.
I work with transmission and power takeoff unit designers, where my job is to determine why bearings fail. Usually the root cause is excessive debris denting. Every opportunity I get, I try to convince them to incorporate at least one fluid change around 30K to 40K to get rid of break-in debris, as Mercedes did when they modified their fill-for-life stance. Their answer is to force all suppliers to guarantee a maximum level of cleanliness in their parts for production. This ignores the debris that is generated during break-in. It also forces bearing manufacturers to supercharge their material. No real estate is given to make bearings bigger.
I understand their position, because the motoring public doesn't want to hear that they have to spend an afternoon taking their car in and spend $200+ on a perfectly good working car for this service, especially when the competitor doesn't require it. This fill-for-life is now engrained into the motoring public's minds.
This means that only us enthusiasts and other people who have critical thinking skills will be changing transmission fluid (if these other people can convince their dealers to do so.... another uphill task).
I always assumed this was the case. That is why when I bought my Mustang, the trans and diff fluids were changes at 5K miles.
