Originally Posted By: Carguy21
Is it real the myth about replacing the ATF after certain number of miles driven on the same fluid, will damage the transmission? I'm very much aware about many people saying it will hurt the transmission, but have you seen any case of a vehicle with a broken transmission caused but an ATF replacement?
Its a myth with a little bit of basis in fact. Old fully-hydraulic transmissions could take a lot of abuse and keep working. They could work with huge internal leakage past seals and valves. On rare occasions, fresh fluid (being un-oxidized, uncontaminated) would leak past a bad seal *just* enough faster than the old fluid so that the transmission wouldn't go into gear once the new fluid got circulated. It was worse when cold, so sometimes the car would drive home from a fluid change and then not move the next morning when all the seals were cold and shrunken. People then blamed the fluid change. But in reality, the transmission was a dead man walking even before the fluid change.