900 foot pounds.
Ok, maybe not.
Technically, there isn't an actual torque spec that you simply crunch it down to. If you're going to be replacing the seal, you'll have to follow the procedure of measuring running torque on the bearings and get that in spec. It's a bit more involved than just grinking down the pinion nut and calling it a day. Getting that thing back exactly like it's supposed to be without further crunching the crush sleeve, or not getting it tight enough just exactly right can put your ring/pinion clearances out of whack and you'll have some singing gears going down the highway and some unwanted wear down the road. If you've never done this before, you may want to enlist the help of a good friend to knows how to setup rear ends. YOU DO NOT WANT TO FUGG THIS UP.
Could you get by where you mark the pinion nut on the pinion stem and nut, then break it loose and count the number of turns to remove, then count the exact number of turns and match up the match marks and get it close? I've known people who have done this and got by with it. I don't personally recommend shooting in the dark like that, but it can be done. If you're still not sure what you're doing, just farm that job out to a GOOD rear end guy. Pay him whatever he wants to do it, it's worth it. May want to redo the axle end seals while you're back there.
Pinion seal- GM p/n 552571, or 26026792
NOS OEM 1975-92 Buick Chevy Cadillac Oldsmobile Pontiac differential pinion oil seal GM 552571. Please verify your exact application for fitment.
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Axle seals- GM p/n 554631 (need 2)
We Take Our Own Pictures of Each Item, We have Every Item On Hand.
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