I replaced my 7.25" rear end with an 8.25" sure-grip from a salvage yard car, and now I have a shudder at very low speed when turning slightly. It seems to go away at higher speeds or in a full turn. Also, it seems to go away after driving a few miles but comes back next time I start out.
Before installing the rear end I changed the pinion seal. I restored the bearing preload very close to what it was before, about 7 in-lbs required to turn the pinion by the nut with the axles clipped in but no wheels installed. I did not change the axle bearings but they looked OK to my novice eye as did the axles and the differential (I pulled the axles to change backing plates). I filled the differential with 2.2 qts of 75W90 gear oil with nonslip additive.