I have a 12-bolt that whines at about 45 mph. It had a pinion leak and I replaced the seal. I am guessing the whine is because I failed to put sufficient preload pn the bolt or should have replaced the crush washer thingy.

What type of shop fixes rear ends: transmission, speed shop or general mechanic?

thx

tranny shop would be your best bet. im not sure and by all means no expert but i think the carrier has to be removed to set the pinion preload and you may need a new crush sleeve. this can all be done at home if you had a dial torque wrench that reads in inch lbs and just replace the shimms in their original locations and a friend who is willing to help tighten the pinion nut. very hard to crush the sleeve
good luck
Steven

You need to get a pinion installation kit. This will have new pinion bearings, crush spacer, pinion nut, pinion seal and shims in it. The differential will need to be removed and all of the pinion bearings replaced. Then you can acurately set the preload on the pinion bearings. Setting preload on used bearings is very difficult because the preload is so light that it is hard to measure and set. New bearings require more preload and will set up much easier. Used bearings usually don't do well when setting the preload again. Preloqad on new bearings is about 20 inch pounds and preload on used bearings is about 2 to 5 inch pounds. Your bearings are probably bad now anyway because you have the noise in the rear end.