while iv just been sitting here at work all night reading the post`s iv got another question. where is the plug or stick to check the fluid level on my `90 L98 6speed trans. also what weight of fluid do i need. i`v also replaced the head gaskets on this car recently if there are any questions while this stuff is fresh on my mind.

First off, the allen head drain and fill plugs on the ZF are 17mm.
And Sarkee, nailed it right on the head how to fill the ZF.
Just jack the car up, and climb under and remove the fill plug on the passanger side of the trans.
One tip is, make sure the car is level. If just the front end is in the air, then the fluid is going to come out when you open the fill plug, and you won't beable to service it.
For the type of fluid. This varies. Check out www.zfdoc.com Bill rebuilt my trans, and he recommends fully synthetic castrol, 5w-30. I know, a lot will disagree with this, because the weight is a motor oil, but the castrol works awsome. the ZF shifts so good now.
Hope this will help you,
Ed

You can get the factory fluid from the dealership. It's 5w-30 but it's not plain motor oil. It'd be worth the extra money to get the correct fluid, remeber thats a 6000 dollar transmission, you don't want to tank any chances.

Since Bill B. rebuilds ZF for a living, I'm surprised he doesn't recommend Olive oil (just kidding). GM OEM & service fluid is 5W-30. The transmission mfr recommmends GM service fluid or Castrol RS full synthetic euro spec motor oil imported and sold by BMW dealers ONLY. It is not the USA blend of 5W-30 Castrol full synthetic sold in various auto parts stores.

Yea Rick,
that is what I meant. The BMW stuff. I bought mine at a BMW dealer for around 8 bucks a quart.

And you need to buy 3 quarts, because the trans holds 2.6 or so. I can't remember right now.
Ed