I have a 91 z28/350 posi-trac rear, restoration in progress. Last december I was turning out of Lowes Lumber onto main road, normal speed, nothing fast and as I turned I got the very hard dull metal sound kick in the rear. Made it home thought could it be posi-trac gone....has about 98k, friend said that it sounds like rear torsion bar, since posi-gears are pretty sturdy gears. My 90 RS did the same thing, but it was rear end (no posi) on 90 RS and once I pulled the rear plate I had all kinds of big metal chunks. Advice Thanks Bruce