GregLo

2001 a8l 165k I have a vibration issue where I can feel even a low speed I can drive approx 2-5mph and i can feel what seem to be the rear moving slight up and down as if i had a out of round tire or bent rim . Thus far i have removed my stock D3 12 spoke rims w/255/40/19 continentals and reinstalled my stock 17" Fat fives Pirelli P6 four seasons" winter set" which i have spin balanced 2 times and are true as a bone.I cant seem to find the problem I'm thinking its either an off center hub or bent axle .is there any of you who have had similar issues if so please enlighten me
thanks
greg

silverd2

Tires would be my first guess, but you eliminated that.
So I'd move on to wheel bearing..but only if it had enough play to actually wobble at low speed or an outside axle bolt (securing CV joint) has loosened, which would destroy the bearing anyway.
A really dry and/or binding rear CV joint could theoretically cause a hopping feeling also.
I'd jack up one side at a time, check for any side play at all, for wheel bearing or loosened axle nut. Also hand turn each wheel slowly to feel for any pulsating resistance...plus look at all CV boots for tears/grease leaks.
You'd probably feel it at other speeds and have odd handling, but give the rear shocks a check also...oil leaks and the old fashioned bounce the car at the corners to check for instant recovery...a blown shock could allow a corner to bounce.
Unless you've been driving down dry river beds, I can't imagine developing an actual bent axle.

GregLo

got it on the lift today and got it up to about 55 with not a wobble but i felt the vibration in the car but could tell if that was the vibration from being on the lift or source of problem let my bud do the same as i watched and everything under and wheels running true but did notice rear diff has been leaking fluid, got me thinking bearing or lack of fluid in diff causing???????????? some binding??????????
F*cK
driving me nuts forgot to mention tire rod ends could use replacing but not immediately

Torsion'sA8

There is a good chance your tie rod ends are causing the vibration, with any play in them it is way to easy for a vibration to get started. Not sure where you are located but this is my first time around ice and snow and I found out it don't take much in the wheel to get really BAD almost violent vibrations.

silverd2

Well, vibration could change or even not be present without a the weight load on wheels or drivetrain not being under a torque load. Did you check for any side play on wheels...on lift, car off, grabbing wheel?

Would be worth checking level of rear diff fluid...dry diffs should make a "whining" or constant "droan" that goes exactly with speed of car.

spitanddirt

Let me throw my two cents in here. I have the standard A8(2000) myself, but I know that my transmission has been rebuilt or replaced at some time before I owned it. Here is the problem I encountered: a vibration that would only really occur between 40-47 mph. I tried the rebalance of the tires only to find they were perfect already. However, I did notice that the Firestone tires that were installed by the previous owner were not constructed very well. I watched them spin on the balancer and could see the tire move up and down, but the rim was perfectly centered on the hub. I can always hear a low speed(quiet) whap,whap,whap sound... up until I get over 12 mph. I've done complete brakes and rotors and replaced a right front drive axle whose boot had torn through.

It wasn't until I started hearing a sound during the wintertime that, quite honestly, sounded like spaceship taking off like a Jetson's cartoon. It only happened when the car was completely cold and would only last for about 10 minutes until the car warmed up. Then I finally heard it on my way home from work: I had the sound of raspy metal ***** clinking around under my car. Sure enough, I found that my center support bearing for the driveshaft (propeller shaft as Audi calls it) had gone bad. To add insult to injury however, I discovered that it may have been actually caused when the transmission was out. When the driveshaft was reinstalled after the transmission went in, no one bothered to replace the shims that were removed from the center support bearing! The driveshaft on our cars is two pieces connected in the center by a single u-joint. The center support bearing is not replaceable by the DIY'er including myself. I had to get my driveshaft remanufactured by Driveshaft Specialist (.com) of San Antonio, TX.

The cost of remanufacturing mine cost $479 with shipping included. I highly recommend their work. Now here's the crappy part: in order to correctly install the driveshaft back into the car, Audi requires you to have a special tool to axially center the driveshaft upon installation. Let me tell you that you can get it close by eyeballing it, but not perfect. If the center driveshaft is off axially, you could experience the exact symptoms you are talking about. I’ve included some pictures of the tool being used. This tool cost me about $250. Still, it’s better than shelling out over $1300+ for just the driveshaft from the stealership.

Just so Audi could make it difficult, the driveshaft is made from two different diameters of pipe. If you look closely, you can see the grey adaptors used to make up the 5mm difference between the two. The exhaust system from the center clamps back has to come out in order to access the driveshaft. Then comes the heat shields and the body reinforcements. You can see in the one picture how many washers I used to shim the center support bearing away from the body for proper axial alignment. Don't forget, it's not just side to side, but also up and down. AAANND, the driveshaft has to be centered front to rear so as not to put to much strain on the CV joints at either end.

I've pulled my driveshaft three times so far, I'm getting pretty fast at it. And by the way, I did it using a couple of XL35 jacks from Costco($100each) and car ramps. I removed and installed the exhaust on my belly while laying on a creeper.