How to rebuild a 8 3/4 Borg Warner Posi Unit

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Blair Harris

Blair Harris

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Hi looking for some specks on how to rebuild a Borg Warner 8 3/4 spin restintant unit. I have read a couple articles that you can Machine the locking unit and get full factory results.
Any help would be appreciated.
Thanks Blair
 
the clutch less differential is actually very simple to rebuild once you dissemble the carrier you will find the cone "clutch" steel cone with spiral cut into it measure the overall thickness machine the flat face of the cone "so it can sit lower in the carrier" remeasure the overall thickness add shim to back side to keep overall thickness the same " pinion shims work perfect I think i used 10.5 ford. If you have access to a brake lathe it works perfect for machining the cones. I add a little extra shim to take the excess slop out of the spiders but don't run them tight it will act like a spool!
 
Hi thanks for your help.
I have it all apart i was guessing that was what i had to cut down to get it to lock up. Just was not sure how to take up the slack i machined off . Any idea how many thousands of an inch it usually takes to get it to reseat?
One other question what did you use for gear oil on your unit.
 
None of this procedure is in any repair manual or even remotely recommended. The cone type sure grip is classified as non rebuildable. Just the same as the Auburn units. Any attempt to do so is shade tree at best. Once the spiral cuts into the case to the point that the cones bottom out in the case ends, that's it, the party's over. Have people modified them so they continue to give sure grip performance? Sure. But they never last and they are never as strong as they were when new. The only rebuildable sure grip unit that's supported rebuildable by factory or aftermarket service manuals AND factory and aftermarket parts is the clutch type Dana/Eaton sure grip unit.


torred0319 said:
the clutch less differential is actually very simple to rebuild once you dissemble the carrier you will find the cone "clutch" steel cone with spiral cut into it measure the overall thickness machine the flat face of the cone "so it can sit lower in the carrier" remeasure the overall thickness add shim to back side to keep overall thickness the same " pinion shims work perfect I think i used 10.5 ford. If you have access to a brake lathe it works perfect for machining the cones. I add a little extra shim to take the excess slop out of the spiders but don't run them tight it will act like a spool!
Click to expand...
 
While Rob's comments are accurate, you can make it work decently. Kudos for trying, you may get lucky, or you may not, but at least you are taking a shot.
I once had someone tell me that I HAD to use a torque wrench on a set of heads. They were absolutely right, but I didn't anyway, and it worked out fine.

I love Truro, absolutely beautiful country.
 
.........I've shaved .040 off the cones, u should shim the springs an equal amount, but Rob is rite, its just a band aid fix.......ok 4 a street car, but 4 racing i dont recommemd it.......kim....
 
Sorry disagree remaching the cone is no different than machining a rotor. For a daily driver 450 bucks for a new posi + new bearings is insane!!!!!! VS 20 bucks in gear oil and a couple hours.. I have done them I know they work! If i'm shade tree I'm shade tree I still rebuild transmissions too.
 
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