Center differential, anyone tackled this?

[Spawne32]

Looking for info on the center differential, realize the front and rear take 75w90 but since the center diff has clutches, what does audi recommend and how do you get the fluid out? Hearing that its vacuum pumped out.

[jfo]

Looking for info on the center differential, realize the front and rear take 75w90 but since the center diff has clutches, what does audi recommend and how do you get the fluid out? Hearing that its vacuum pumped out.

The center diff has Sturaco friction modifer added to the standard 75-90 fluid, to reduce stress in the limited slip diff. It's expensive at the dealer. I have read that it isn't required unless replacing/rebuilding the diff, but can't confirm if this is true. I asked ZF and they were vague, suggesting that I use the OEM fluid. So, I will take the conservative approach and buy the dealer fluid....probably $60/l vs $20 for the gear oil only. Since it's small $$ and a long time between changes, not worth it to risk it IMO. If the friction modifier is not sufficient you will get some noise or shudder with tight turns.
There is a drain plug on the center diff, but you need to drop the trans support to access it. The fill plug on the side is also not easy to get to. I have done the front and rear but haven't tackled the center yet. The next time I'm under the car I will look more closely at the room available for the fill plug and getting a tube in there to extract the fluid.

[Spawne32]

I would normally take it to the dealer for service for this kinda thing, but generally i do my own fluid changes unless they are ridiculously hard. Might have to get a quote for this along with a trans fluid flush.