1988 D100 rwd with 8 1/4 Carrier bearings

I replaced scored pinion bearings and set the pinion up ok. My problem is when I adjust the backlash. Everything goes fine until I torque the adjusters to 70ft lbs., with the brng. caps tightened to 100 ft lbs. Then
the bearing cups will not stay in position, they push in and lock the carrier up. On close examination it looks like the cups may have turned (spun). Otherwise the cups and carrier bearings look good. I'm wondering if I inststall new carrier bearings and cups if the new ones would hold or will I be wasting my money because the casting is shot?
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are you sure you havent swaped the caps on the bearings right to left? by accident maybe?

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Thanks for the comeback Chris. The bearing caps were marked before removal and were not switched. Also the cups and caps were thoroughly dry before installing them. I thought maybe some oil was creating the problem so I took it apart to make sure they were dry.
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I went ahead and replaced the carrier bearings and cups also. Everything torqued down ok with the new cups in place and the rear end is now smooth and quiet.
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