I was trying a different set of wheels on my 88 formula 350 today and noticed some strange things. First, I thought i had might as well see if it was posi since both rears were up, when i turned the wheel there was about a quarter of a turn before the other grabbed. While turning the wheel forward i could feel a light rough spot. I've only put about 100 miles on the car since I've had it but there are no unusual noises other than a clunk which I blame on my loose u-joint that needs changed. It clunks when put into reverse and when i lift off the gas to hit OD. Its not posi though it does leave equal length marks when i'm being abusive with it. Not sure what rearend is in it, all stock as far as i know. Any advice?

 

It could be a posi that has a lot of wear on it. You can't judge what is in a rear end by turning the wheels. This will fool you. The only way to be sure of what you have is to remove the cover and look inside. A worn limited slip differential (posi) will allow the wheels to turn in opposite directions when turning them by hand, but still leave 2 black marks when doing a burnout. Take the cover off and see what you have. I'm guessing that you have a worn Auburn if it's a 10 bolt or a worn Borg Warner if it's a 9 bolt.

 

If I feel up to it monday after work, i'll put it on a lift and check it out. Could a worn lsd also cause the excessive play and light grinding? My 83 RX7 had a stock lsd that was failing but it resulted in a single burnt tire when exiting corners. When it was in the air, both wheels turned together. Seems to be opposite on the 'bird. I'll report back my findings when I can.