Autobox fluid change.

[Old-Guy]

Last time I changed the fluid in an autobox was in about 1980 (BW T35) - having the real workshop manual helped. I bought the car (Hillman Hunter Estate) cheap because the autobox was playing up and its sump gasket was weeping. Sump off, clean it and the filters (loads of sludge) and drain torque converter as far as possible (can't remember how, as it was a while ago). Still left quite a lot of ATF in the box because it didn't need anything like the full qty. Sump paper gasket was ridiculously cheap, though the ATF wasn't! An almost miraculous improvement, no hesitation, instant kick-down. Used the car for daily commuting for over a year - can't remember why it had to go, rot probably.

Changing any fluid, it's worth making a big effort to remove as much of the old fluid as possible. If it's only possible to drain off 80% of the old fluid, then after successive changes, the renewed fluid is still 20% original stuff, then 10%, 5% and so on. This is why the oil in a diesel engine quickly turns black soon after a change - it's the small quantity of black oil left behind coating every surface, in the pump, oil-ways etc.