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

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