Junkyard posi, how to pick a good one?

I'm probably going to just buy another axle for the challenge truck. I can get a posi from the junkyard, but what is the best way to tell how much life is left in it? Looking at GM stuff.

If it's a clutch type lsd then have one guy one side and the other. Twist an axle, while holding the other side still. If an axle can rotate while holding the other axle still, the clutches are shot.

Also, for clutch types, change the fluid. And if you want better lockup, skip the friction modifier additive. Or just put less in.

We usually have one guy try to hold the wheel on one side while the guy on the other see's if he can spin the wheel. Not 100% sure this works for cone type posi's. Check the pinion for slop too, usually a good sign the rear axles worn pretty far or abused.

Well a couple I was able to spin one side and the other didn't move.

If you're looking at truck axles I think most will have a gov lock in them (an automatic clutched locker), not a regular "posi" clutch LSD with preloaded clutches. I also want to say a lot of the F body LSDs are a torsen style ("zexel"?) which will just spin like an open carrier.

If you're a gambling man I've read of making tired clutch LSDs strong again by shimming up the clutch packs.

Gov-Loc are GM'S Auburn cone style limited slip. It slowly eats into the case rendering it useless and esentialy, open. They are not rebuildible. Odds are that the axle is stock, and the posi is toast. I'd look at the mileage. Anything over 100,000 is probably gone.

If it's in the junk yard good chance its worn out. For a limited slip with clutch packs sometimes the packs can be rearranged like in a ford 8.8 so that more of the friction sides make contact with the steels. I've also cut up beer cans to make shims to preload one back to stock or even tighter.

Appleseed wrote: Gov-Loc are GM'S Auburn cone style limited slip. It slowly eats into the case rendering it useless and esentialy, open. They are not rebuildible. Odds are that the axle is stock, and the posi is toast. I'd look at the mileage. Anything over 100,000 is probably gone.

Not quite. Gov-locs are not Auburn "cone style" diffs. They are lockers. They operate like an open diff until they suddenly don't. Auburn cone style diffs, common in older GM cars with "posi" or G80 RPO code, are similar to clutch-plate LSD's, in that there is always some friction. But once the cones wear out, they're done, no rebuilding possible. Yeah you can shim the springs to eek a lil life out. Clutch-plate LSD's, like what are found in Fords, are servicable.

Left to right: Clutch-plate, Auburn friction cone, Gov-loc

I've also cut up beer cans to make shims to preload one back to stock or even tighter.

Now you're talking!

I might do this to my 8.8. But I'll tell you this, the best thing I did was not add any friction modifier. No FM means the clutches can grab better. But shimming would help too