vibration at 25-40 mph

what did U do to help the pinion nut from not loosening with such a small amount of retightening? check it again for tightness. 6-8 turning-that is pinion and? ring gear? axles? the 8 1/4 has a crush sleeve

I left the old crush sleeve in there. I measured the turning torque at about 6 in-lb (to turn the pinion, differential and axles without wheels installed) before I took the nut off, and I also marked the nut position with a punch. After I replaced the seal I torqued the nut back to its previous position (with the same number of threads showing of course). That took over 150 ft-lb. Then I measured the torque required to turn the pinion again, and it was right around 6 in-lb still. Then I loosened the nut one more time, applied red Loctite, and tightened the nut down to the same position.