After driving my 99 with a posi rear for a while when I pull into a parking lot or just generally turn sharp it kind of groans and shudders slightly. It is definitely coming from the back of the vehicle, and it stops the second I go straight again. This tells me it is in the rear differential. I don't know much about posi's other than I think they have clutches in them that slip, making it LIKE a differential, just....tighter. I will tear into it, check that everything is tight and has the right backlash and everything, and change the fluid. Any other heads up I should be looking for while I'm in there? Don't know much about posi's, but I have done transmisions and setup ring and pinions and stuff like that. Thanks.

Mopar has an additive for the limited slips. Might be all you need. When's the last time you changed the fluid and did you use the right stuff?

Just bought this vehicle, today was the first drive into work with it. So, no idea what is in it. If nothing else I was going to change the fluid with the right stuff, and while I was in there, just look around. Actually, I noticed today that it seems to do it more when turning partway, not all the way sharp. A few people that I have talked to today say that is normal for a posi rear car, especially a relatively short wheelbase car, and others say no way that is normal. Seems like a short wheelbase car would have a bigger differance in inside wheel speed versus outside wheel speed. Plus Jeeps turn in pretty sharp compared to a long pickup truck which is more common to have a posi. I am babbling now..............

What do you mean by POSI. The stock LSD, which sounds to be working, but in need of oil and additive. OR are we discussing an aftermarket unit?

"Posi" or "Posi-Traction" is a Chevy brand name for their version of a clutch type limited slip diff. I believe Trac-Loc is the Chrysler/Jeep name.....either way, they are both limited slip diffs. I'd start with a clean out and gear oil change. If it still makes a noise, and u are positive it is a factory LSD, then poll the plug and add the small tube of friction modifier. If the LSD doesn't chatter in a turn, it doesn't need the modifier additive as the additive just makes it slip more/easier which means slightly less torque to both wheels (in a turn).

Change the gear oil (75w-90) with a friction modifier and you should be good. Mine did that when I first got it too, changing it made an immediate difference no more noises.

Well, the guy I bought it from said it was a factory "posi", I guess that means it is an LSD as was said, they are basically the same thing. When I turn corners on dirt roads the inside tire spins a little, so I am sure it's not just a standard open diff.

Agreed change fluid with the right stuff and additive and all should be better.

Spinning 1 tire in dirt sounds like an open diff or possibly a worn out clutch type lsd. Even a worn out lsd will spin both wheels the same direction when the axle (both wheels) is raised. Open diff, wheels spin opposite direction.

I just verified that it is an LSD.
When I say "spin the inside tire" I don't mean step on the gas and just the inside tire spins, I mean just idling around the corner the inside tire just turns over a little bit. When I hit the gas, both tires spin.

My Auburn LSD was making the same noises. It has about 4000 on it. I changed the break in oil at 500, and it started making noises about 3500. I put 80-90w with 6oz additive in, just like the book said. Took it over to OK4wd, and opened it back up. Everything looked good, so we put in Amsoil 75-140w, and 8oz. of additive. Nice and quiet now, and still works the way it should. I don't crawl over really tough stuff, because it is my daily driver. If I did I would have bought a real locker.

Post a pic when get the cover off.....who knows, u could have a "real" locker.

Finally got it apart. Kind of looks like a regular open differential to me. That's bad news. Other opinions? Looks like just regular spider gears to me.

Looks like a limited slip carrier to me.

Its a trac lock

Yep, looks like the factory clutch-type LSD (kinda squared off). Here's a before/after C8.25 open/locked.