Auto Trans Fluid Change?

[canada karl]

I have a 530i with a leaky ZF 3HP 22 trans oil pan rubber seal gasket. Seems I have lost a fair bit of fluid. Problem is there is quite a bit written about replacing new fluid in a high mileage trans because it tends to act as a solvent and loosen everything up in there so that it gums up the works. Apparently trans shops make you sign a waiver when they do a change with a high miler. Anyone out there with an Auto had a bad experience with this?
Hopefully I haven't lost that much fluid and I can just recycle the old fluid I drain out??

[Mike W.]

It seems much of the reputation of trannys failing after a fluid change is because people take it in for a change after it's already suffering and starting to fail. With all the horror stories, though most of them urban legend, it can take a leap of faith to do a change, but it's a good thing. Trannys like clean oil. Grit between wet clutches doesn't make them work better. Now pressure flushes may or may not be a source of problems, but just a fluid change is not. And with the oil in the converter which doesn't get changed you're only changing about a third of it anyway.

I had an E21 some years ago with a ZF 3HP22, same as in E28s, just with a smaller torque converter I believe, that when cold used to skip 2nd gear. After a half mile or so it shifted normally. I started changing the fluid when I did engine oil changed, I'm not even sure if I even changed the filter, and after about the 3rd one it started acting like it was supposed to. So fresh fluid may clean things out a bit besides get the dirty stuff out, but it sure wasn't overnight for me.

[canada karl]

Thanks for the info Mike. I feel better about doing the change now. Might as well change the filter while I'm in there. Where's the best place to get a filter for for a ZF?

[garyinwestoz]

well having replaced oil in 2 auto boxes in the last year - its rather easy to do - The hardest thing is working out how much fluid to put in, as reading the dipstick is difficult - some say that top up fluid whilst engine is running so that you have enough fluid.

A. was having trouble with not engaging fast enough - particularly reverse.
B. only engaged 1st, could drive for about 3 mins, all drive to wheels stopped.

I ended up removing pan then valve body and cleaning all the hydraulic value body components, reassembling and then reinstalling in the car. One took over 4 litres of fluid to refill it so it all worked okay again!

A. is much better - forwards is nice, quick and smooth. Reverse - struggles a bit when cold, but after a few minutes seems to engage quickly.

B. now engages all 3 forward gears - reverse still a bit dodgy

If changing the pan gasket - take pan into shop and make sure it fits. I got one that had shrunk and wouldn't fit ( too long on shelf perhaps) - they replaced it with one that hadn't shrunk - a bit of waste of time finding that out!

[canada karl]

Is there ab actual oil "filter" in the trans or is it just a screen?

[HB528i]

It’s just a screen