When I turn the wheel all the way to lock, there is strong vibration in the steering wheel that seems to shake the whole car. When im making a U-turn, the same thing happens when I have to turn the wheel all the way to lock.

Also, the steering begins to shake above 60 MPH.
Any suggestions?

1998 Audi A6 2.8L quattro sedan

 

The first set of symptoms are indicative of a locked differential. Ouch!

The second set are control arms. You have to replace with a good set. Fix the differential probelm first as you might decide to get rid of the car instead of going the cost of repair. A rear diff won't be too bad but yours sounds like a center diff (the Torsen diff) and that is inside the transmission and might require dropping it, at which point you might be better off trading the car in.

Good luck,

Bob