I recently had my A8 on a lift checking the front end. I have a vibration at highway speeds (most prevelent at 55-70mph). When i got to the front axels i found a little bit of play on the drivers side output flange, and alot more play on the passanger side. It moves enough to make a clicking noise when really trying to move it. Other that that the axels/ cv joints seem solid. Could the flang somehow be bad or the bolt that attaches it to the front diff be loose or streched?
Any input would be a huge help.
2001 A8L 48xxx, well kept nice car

 

I already plan on replacing both axels when i save the money up

 

Don't make any rash decisions yet.

Play? 3 kinds to choose from: In/out...side to side...radial? ...none of these necessarily causing your problem, unless only under heavy acceleration or deceleration load, and changes by going from one to the other or no load at all (coasting). Gear oil leaking? Radial play is normal...a little side to side, even a click is not necessarily critical. Flange retaining bolts rarely ever loosen or warp...not under any load themselves...inside joint slides back and forth on shaft under suspension changes and load is all radial...not push-pull.

If vibration is constant regardless of load or no load, could be tire(s)...front end vibration only? ...tried tire rotation front to rear?

Changing axles? ...any ripped boots on drive joints? Bad joints tend to click/clunk during turns or turns under hard accel or decel... and rarely EVER go bad if boots are intact. Original axles are of infinitely higher quality (and pretty much bullet-proof with intact boots) than ANY aftermarket...even "Raxles" brand, not even close. Bad drive joints are not likely to cause any kind of straight line vibrations.

There are bearings for each drive flange, just inside front differential which are changable without removing transaxle. Don't know if they'd cause your vibration without a lot of noise, too(?)

Transmission problem would likely be more rpm/load sensitive rather than speed. Differential on out to tires would be speed sensitive.

All theories, but axles/joints themselves are the least likely culprits...tire(s) most likely.

Hope something here helps.