If that vibe is under hard acceleration, it's due to spring wrap. The pinion can rotate easier now that the springs are under the axle, and the torque is wrapping the nose of the diff upward as it accelerates....
Ok some food for thought (mmmmm, foooooodddd)
there may be slop in the slip joint (since the drive shaft may may have less spline in the upper shaft) sometimes fixed by spacers
or the u-joint angles upper and lower may be rather extreme (sometimes fixed by shimming (putting little pie/angled chunks of steel in the spring perch to spring pack area) I've got about 6* or so shimmed in the rear of mine 4.5" and no drive shaft spacers.) causing some vibes. Ya may have a bad u-joint, drive shaft could be out of balance, you may have put the drive shaft halves back together wrong (there **should** be a small indention on both sides of the shaft, put them together so they are matching).
Couple of questions since I have the same problem.
What did you use to Shim the axle??..>
Did you shim the back to poit the nose down more, or the front to point the nose up more??...
How do you keep the spring packs from coming loose from the perches if they are shimmed?
94 SPOA 33" EFI Sammi (Mine)
91 Stocker Sammi (Wife's)
Fuel Injected is the only way to wheel.
I'm sorry, I kinna half assed my shimms. I cut 2" sections of a tire iron, welded them to the rear perch and then took some say 1/4" or so plate steel and welded that to the front of the perch and on the top of the tire iron sections. I figure I have about 5* or so ish.. The purpose was to raise the pinion..