99' A8 bad center diff???
 

Hello all!

I'm Jeff and I live up in wonderful New England, Southern NH & Northshore Mass area. I just picked up a 1999 D2 A8 in Volcano Black with over 200k on the dash. I've already upgrade the interior door cards to S8 Alcantara examples and a D3 wooden trim steering wheel that looks awesome in the car. I also just finished upgrading to a FL center dash/radio/hvac setup. Just need to finish up some wiring. Lowered on ST coils and 20" BBS RS knock offs. Bunch of other things I need to do but i'll keep this intro short for now.

First, I apologize for this being my first post on Audi World but I need some insight.

Now down to business.

So I bought the A8 for a cheap $600. I know the owner of the car so he gave me the details of what he's done and maintenance history. Reason he sold the car is because he began to hear a odd metallic noise from under the car. Now he did rebuild the transmission 2k miles ago according to him and its been driving fine since then. always serviced in a VW dealer so the tech apparently had 30yrs under his belt that diagnosed the car with a bad center diff when it was up on a lift. In drive while in the air the tech could hear the noise from the center diff and no where else so its been pinpointed as the issue. I had the car towed to my shop since it was 3hrs away and I work odd hours. So fast forward to last weekend. I take the car out to try and hear the odd metallic noise under the car. drove around my block a few times and heard nothing. didn't go over 40mph but the PO stated he heard the noise at low speeds. So I confirmed the noise was not normal.

After doing a lot of research it seems the output shaft seals is a common issue. Now I'm wondering if my seal is bad(I haven't gotten far enough under the car to look at the tail shaft) and maybe it leaked out a good amount of gear oil. So I know of one car that had the center diff destroyed due to low fluid levels but I cant find more info on what happens when the seal is ignored. Do these diffs start to bind up and then???? BOOM? Do they start to make a metallic rotational noise when the fluid is low? the PO said he heard the noise and immediately parked that car, since he owns a D3 as well.

Plan is to drain the diff fluid Friday, measure how much fluid was in the case. Check for metal in the fluid and if there isn't any I will refill and go from there.

Any further insight into this would be wonderful! Links, video, photos

TIA!!!

PS: I should mention I picked up a built trans from guy. Its a upgraded D2 S8 FL trans worth a pretty penny. Thinking about swapping this into the car along with a Euro TCM and rear diff. not sure if its worth the hassle since my current trans was rebuilt 2k miles ago.