I have an 83Z28 with a T5 and 10 bolt posi rear. I just replaced the motor recently and haven't really driven it over 60mph..until today. Above 65mph I get a REALLY bad vibration, the whole car vibrates and it seems to just get worse as I increase speed. It does not go away when I put it in neutral, or a different gear. The car does not vibrate at all until I reach this speed, no matter what RPM I am at. I have brand new tires, new ploy trans mount and poly torque arm mount. I just changed my ujoints last weekend to fix a clunking problem. However when I had the drive shaft off, I noticed some up/down movement where the driveshaft mounts to the rear. I put a ratchet on the pinion nut, and tightened it about a half a turn; the movement seemed to go away. I also noticed that fluid had been leaking from this area. Would a bad outer pinion bearing cause this problem? I also hear a whine coming from the rear at all speeds, that doesn't seem speed specific. Any help would be appreciated greatly, Thanks

 

if you have a leak from the pinion seal could be a bad bearing...that whine could be caused by a low fluid level in the differential...you said it was leaking, right? Take the cover off and have a look. New gasket and a couple qts of gear oil isnt too much to pay

hmmm the vibration could also be tire balance, a tire out of round, a bad wheel bearing, etc etc etc