So I did a complete frame-on restoration on my 71 GS recently. One of the few things I did not replace were the body to frame bushings, which still looked pretty good at the time. After driving it around a bit, I noticed popping and grinding coming from the rear of the car, especially when going around corners at high speed. I checked the spider gears and rear bearings, which were all good. I decided it might be the old body bushings. I hated the idea of tearing the car apart to replace them after I had finished it, but I decided it needed doing. I replaced the body bushings (with new rubber bushings). Although the old ones looked good when I had the car disassembled, after driving it for a bit, they started to disintegrate since the car hadn’t been driven in 20 years and the bushing were pushing 50 years old. Another lesson learned the hard way. I can’t believe the transformation with the new bushings. Aside from the popping, grinding, and squeaking that is now gone, the best thing is that the sloppy steering that had been driving me crazy is now tight like a new car with rack and pinion. I previously replaced the entire front and rear suspension, bushings, shocks, steering box, steering pump (which were all shot), and had it aligned, but the steering was still sloppy and kind of scary. Remarkable how much the body mount bushings affect the steering.
$130 on ebay. You have to order the ones for a Chevelle convertible to get the right set. They are correct, but have "chevrolet" stamped on them. I'm usually too busy to get pictures until after I'm done.
Thanks for posting. I've been trying to figure out what's causing my car that spongy, sloppy feeling, and your right about that being scary. My shocks, springs, and suspension are in good order, and never thought about the body bushings. Mine are definitely shot, so looks like another project added to the list.