I just spoke with a retired vehicle service manager for a large city. He said they were advised by truck/auto manufactures, and privately by oil companys, to not change auto transmission fluid. He said they'd remove fluid, filter it and put it back in the truck with a new transmission filter. This sounded crasy and I asked how this could be good. He replied over time the transmission wears, gums up and seals thin out. By putting in new fluid, the new additives would break down the gum, cause leaks in seals and basically mess up the transmission. Is this reasonable?

Thank you

 

No. Yes trannys wear. Anything mechanical has wear due to normal operation. Thats why it is so crucial to maintain good lubrication. As your tranny fluid ages with miles and heat the additives in the fluid breakdown. Just like engine oil. You dont take it out filter it and put it back in do you? Of course not! Yes the seals age. Its mechanical. As far as 'gum' and tarnish go, regular fluid and filter service will more often than not help prevent buildup. As long as the fluid isn't burnt I dont see a problem.

 

My father tried this with his work truck and put about 150,000 hard miles on his truck and one day thought he needed a new trans. Took it to the shop and did a full flush and it's as good as new.