So, I bought my 2000 A8 about a month ago and decided to take it on our family vacation to save a few bucks on gas over our Yukon. Once finished packing and stuffing every nook and cranny, we headed out on our adventure from the midwest to the Colorado Rockies. We were making good time and the Audi was doing great (getting 27.5 MPG at 80mph). We were a little over halfway thru Nebraska when the battery/charging lamp came on and I noticed the steering become a little heavier. The nearest town was Lexington, which was still around 30-35 miles away. We turned off anything taking power from the battery that we could, other than the engine and headlights and proceeded on to town. We were trying to find anything we could for a auto repair shop and were pleased to pull into the Advance Auto Parts store there still under power but not wanting to shut it down for fear the battery wouldn't have enough to restart the car. I was able to borrow a flashlight from the store to check and see what had went wrong (no charging, no power steering, I assumed the belt had broken). Upon inspection, I found the belt was still intact but the tensioner pulley was missing! I had them look it up and the closest one they could get would take four days for them to get! WE WERE SUPPOSED TO BE ON VACATION! The Audi started right up, so we left to go find a hotel for the night and to think things thru and weigh our options. The next morning I started calling all the local parts stores and auto recyclers with no luck on finding anything. I then extended my search and even contacting a couple of dealers with the same time frame as the Advance parts store. After praying for God to help us out and get us up and going again, I located a used part in a town that was only 40 miles from our home and they said they could overnight it to us if needed, BUT, I had one other thought come to mind and that was to see if instead of replacing the whole tensioner, maybe we could just replace the pulley. Well, guess what, after taking what was left of the pulley (outer was laying on the lower shield and the inner was still on the tensioner) into the store, the kind lady working there walked to the back and came back just a few minutes later with three pulleys in her hand. The first two were somewhat smaller in diameter and may have worked but the third one was sooo close to the original that you wouldn't know the difference without a micrometer to measure it! I took the part out and put it on, got everything reassembled, and started the car... WE WERE BACK ON VACATION!
So here is the part interchange info that you may be able to use someday...
The pulley was made by Dayco and is part # 89010. I used some thread locker on the bolt when reassembling and finished the trip without any other issues.
Hope you enjoyed the story and can find this info somewhat useful. Bud