Posted By: ultrajosh
new 8 3/4 chunk - driveline vibration - pinion angle? - 06/03/17 04:24 AM
I just swapped a 3:55 sure grip into my 8 3/4 rear (had a 2.94 sure grip before) and now I'm getting a noticeable driveline vibration when coasting downhill in gear (under load/uphill it's less noticeable), in neutral it stops. I tried flipping the u-joint/driveshaft 180deg but same thing. It seemed like the pinion/nose was pointed up about 7 or 8 degrees after the swap, but that seemed different to me than when I was originally taking the chunk out - I remember it looking basically flat. Could I have tweaked the angle of the housing by jacking the car up by the axle when I had the pumpkin out, like maybe it slipped in the u-bolts or something? Could this cause the vibration? I read somewhere if the trans is pointing down at the rear a certain # of degrees, then the pinion should point up the same number of degrees. Or they should both point down the same # of degrees... or something like that - I forget which. Is this something I can adjust by loosening the U-bolts and rotating the axle a little? Car has six-leaf springs but pretty soft shocks, at the moment. I've never had to adjust this before when I swapped pumpkins but maybe I got lucky? Or could it be the universal joint?