I have a 94 GT and just rebuild and upgrades the rear end for future mods. I put a EATON posi with SUPERIOR 31 spline alxes and RICHMOND 4.10 gears. everything was good and followed the brake in procedures for the gears. i have put aroung 300 to 400 miles on them and a few burnouts. here is the problem i started having. driving is fine but if i stop and back up i get a CLUNK and the same when i go from reverse to first (5 speed man). i put the car on a 4 post rack and it is comming from the diff section. i pulled it apart and the back lash in the gears is with in spec and the gears still mesh properly. the play i noticed is in the spider gears to alxe. i checked with eaton and superior had me mic them and were in spec. has anyone else had a problem like this.

Thanks in advance.