Dope

iTrader: (2)

Hey guys,

I have a 98 SS M6. Basically stock (just CAI, catback, that sort of thing). It's been my DD for many years. Over the past few years I have developed a whining rear and a vibration at highway speeds.

So far, I have replaced/fixed:

1) Entire rear out of an '02 donor
2) Driveshaft u-joints
3) Tire rebalance
4) Swapped tires front/rear

Not only has this not helped, it is actually worse now. When I say it is a vibration, it's really worse than that. The car literally shakes/shudders over 40-50mph. It is dependent on speed only. RPMs don't make a difference, gear doesn't make a difference, being in neutral or not does not make a difference, on/off the brakes or gas does not make a difference. Just speed. At low speeds it is fine (or at least not noticeable). It is undriveable on the highway. It's worse than driving on the rumble strip on the highway in fact.

It is definitely coming from the back. No vibration in the steering wheel at all, but you can feel it mainly right in your butt through the seats. The empty passenger seat wobbles all over the place.

Thoughts on next steps? Rebalance driveshaft and then what?

*boggle*

Edit: forgot to mention, I do have a poly tq arm mount and trans mount. They have been in the car for almost 10 years though. Not sure if it matters.

Thanks,
Dope

Bob@BruteSpeed

iTrader: (16)

Factory or aftermarket torque arm? The factory torque arm is made out of stamped sheetmetal and I have seen them bend approx six inches ahead of the rear end. This will cause the front of the rear to angle upwards, I had one come in that was so severe that the springs were about to fall out of their spring pockets. A torque arm that throws the pinion angle off just a few degrees can cause a real nasty vibration. You might want to see if this is your problem. Bob

Dope

iTrader: (2)

Factory torque arm, yes. I just replaced the rear this weekend, and the arm looked fine but I suppose I wouldn't notice a few degrees off. Guess I'll buy one of those magnetic pinion angle things and check it out. What is the factory pinion angle?

Dope

Bob@BruteSpeed

iTrader: (16)

I don't know for sure what the factory torque arm's pinion angle is at, but I would think it would be around a -1. Bob