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I have a slight clunking noise in my rear when shifting from first to second. Also a vibration above 75. The whole rear of the car has been rebuilt. When I took the tires off to look around the only thing I noticed was the crossmember that holds the rear pumpkin in the car has a 1/4 inch gap to the frame. I don't remember it being there, but I never looking at it closely before. Could the rubber bushings have went bad?
If just rebuilt I would check the torque of the various bolts to be sure they didn't loosen up,particularly the front snubber bushing/bolt. I doubt the crossmember bushing is bad but the mounting bolts could be loose.
Good luck and let us know what you find.
Gary
I have a slight clunking noise in my rear when shifting from first to second. Also a vibration above 75. The whole rear of the car has been rebuilt. When I took the tires off to look around the only thing I noticed was the crossmember that holds the rear pumpkin in the car has a 1/4 inch gap to the frame. I don't remember it being there, but I never looking at it closely before. Could the rubber bushings have went bad?
I would venture a guess that the clunk when shifting is caused by a bad front differential mount. As you mentioned, your differential is mounted in the car via the rear crossmember but the front is connected to the frame by a front snubber. This is a round "doughnut" with a steel insert and is often shot. Does your car clunk on acceleration and deceleration? It is a $20 part that takes less than an hour to replace. The GM Service Manual covers this repair quite well. I have been surprised at the fact that some cars are still driving around on their original front differential rubber mount. Check it out and let us know. It is an easy job but still a PITA. Btw, the small gap between the rear crossmember and the frame is normal, as far as I know.
I'll have to keep looking into it becaused the front bushing was replaced during the rebuild with a poly bushing like all the rest. I checked the torque of most of the bolts and didn't find any loose ones..