just put in a used rear end in my 85 camaro. never vibrated before but old rear end had a blown out axle bearing where the driveshaft yoke goes into the rear end. i think this may have thrown the driveshaft off balance from driving on it broken for awhile. when i swapped out the driveshaft for my older driveshaft the vibration cooled down a little. the vibration seems to be worse at lower rpms like 45mph in 5th or 60mph in 6th. anyone have any ideas?

 

Did you re-use either of the u-joints when you swaped driveshafts? The rear U-joint from the old diff probably took alot of abuse running with a bad pinion bearing.

 

No the other drive shaft had its own u-joints I did visually inspect the u-joints and they didn't seem to sloppy but it could be the problem