C2 rear noise

[James J.]

Wrote in a few weeks ago looking for possible causes of a rotational thumping coming from the rear when driving.
Got a few suggestions mostly saying to check the front differential mount cushion but, that is not the problem.
After checking the front mount and looking for broken or cracked welds on the cross member I noticed that the forks on the spindle bearing housings are at a slight forward angle instead of being straight down as I suppose they should be. I figured that would force the front of the differential up closer to the drive shaft tunnel than normal. Sure enough when I dropped the front mount, there appears to be scrape marks where one side of the yolk is hitting the tunnel.
Any suggestions as to the cause and a cure?
Thanks Jim

[Joe L.]

Re: C2 rear noise

James-----

I've never seen or heard of a case in which the rear spindle support forks were bent or otherwise distorted. However, the bearing support is manufactured of cast nodular iron, so I suppose that it's, theoretically, possible. IF this is the underlying cause of your problem, then the only solution is going to be replacing the bearing support.

More often, contact between the pinion yoke and driveshaft tunnel fiberglass on a mid year is caused by cracked fiberglass in the rear floorpan area. Paragon sells a booklet for a nominal cost to assist you in diagnosing and repairing this problem.

[James J.]

Re: C2 rear noise

Joe, thank you for your response. I did'nt meat to say that the forks were bent, only that the torque arms are tilted so that the forks are pointing slightly forward instead of straight down at the ground.
I was thinking that this was causing the yoke to point upward as well.
Jim

[John H.]

Re: C2 rear noise

Jim -

There's no connection at all between the angle of the forks on the spindle support and the angle/position of the pinion nose; the only parts that determine the pinion angle are the crossmember to which the top of the diff housing is bolted, and the diff nose bracket and bushings. The other contributor to issues there, as Joe noted, is the classic/chronic C2 floor pan sag and/or crack, which causes the tunnel area to drop down above the rear U-joint.

[James J.]

Re: C2 rear noise

Thank you John & Joe, I will check the floor for sagging.

[David H.]

Re: C2 rear noise

I'm NOT a mechanic or expert by any means, so take what I say as a suggestion. I had a rear noise that appeared when I coasted or braked, but stopped when I accelerated. A very pronounced thumping. A friend suggested a worn bearing in the trailing arm (front where connects to frame). Since I needed a new rotor anyway, I removed it, sent to Bair's, re-installed, and seemed to correct problem. Something you may want to consider. Good luck!