Just a heads up, if your suspension is all factory original there is a LOT of rubber that will ultimately get replaced to return the ride to "new".
My impression after reading these forums and personal experience is that vibration is something rotating at speed that is not balanced & rear end steer is usually the result of worn suspension rubber. Does the vibration occur at wheel speeds or about 3x faster (driveline)?
The differential bushings (4 total) are probably shot if they've never been replaced. There are two in the rear where 12 mm hex head bolts hold the diff to the subframe. Torquing these bolts will cause the diff to rock back and forth if they are worn out. Two mounts at the front of the diff do wear out but don't have the same effect as the rears and some mechanics never change them.
The rest of the suspension bushings are the 10 links of the multilink suspension, 5 per side as follows - torque, thrust, camber, tie rod, and spring link (lower control arm). Of these, the torque is the first to wear out, followed by the thrust, camber, tie rod, and lower control arm. However, the usual symptom here is rear end steer, not vibration.
If the center support bearing or mount are worn out (these are located under the exhaust heat shield), that could cause vibration at about 3x wheel speed. The bearing is suspended in a study rubber mount. Sometimes the bearing gets real loose or the middle of the mount separates and it feels like a thumping from the rear of the vehicle as the driveshaft 'whips' around.
This work can cost about $1300+ parts/labor or more, depending in your indy. If the camber, tie rod, or lower control arm joints are touched an alignment is necessary.
I would still rotate the tires to see if that changes the vibration or run the car on the lift and see how smooth the tires run. Overall, I would be suspect of any mechanic that I go to the first time, epecially with a newly acquired car. Moreso when he tells you need your rear suspenion rebuilt to solve an osciallating vibraiton... maybe I'm paranoid.
Last edited by md21722; 01-28-2003 at 12:22 AM.