rear axle fluid change

I'm changing the rear axle fluid. The car has 83k miles and based on the gasket having no slits at the sides, I'd say it has the original fluid. It is kind of greenish, I'm assuming that is the limited slip and that's normal. (first car I've actually had with posi)

So replacing the fluid, I got the one labeled limited slip. Do you all think that is good enough, or should I also add some of the limited slip additive?

Thanks

Get the additive.

The first time I had the diff fluid changed on my 92, the "mechanic" at the lube shop assured me no additives were needed with the limited-slip compatible lube. WRONG. I started having strange issues when cornering etc. Took it in under warranty, dealer found a mess inside the diff. No additive, no warranty. Back to the lube shop, they called the oil manufacturer who basically said "it works in most limited slip diffs, but not all". Expensive lesson -- much more than the cost of the additive. Get the additive!!!

Yes the posi additive will help the clutches slide or slip so when you go around a corner
the rear wont chatter. Also I like to use Mobil one or another good synthetic gear oil.
The synthetic is a little more expensive but your not changing the rear fluid that much,
so the cost difference is not very much per mile. ed

if using full synthetic,. make sure the additive is compatible.
IIRC,. full synthetic doesn't need the additive,. but Semi synthetic does.??
If am doing a rear gear oil change,. and the inside is very scummy,.
i use varsol/diesel/gas etc to wash it out good, can of parts cleaner works well too.
I prefer to use silicone instead of a gasket,. giving the bead a good 15 mins to get a skin on it
before re-installing the cover.
YRMV
JMHO
NWEOI
PDCC

nick

Put the posi additive in first, then add the gear lube. You don't have to worry if you got too much gear lube in and not enough room for the posi additive.

Go to Harbor Freight or similar and get some Nitrile gloves; once you get the rear cover off, reach in with your fingers and scrape out the remaining oil and all of the clutch dust that accumulates in the bottom of the housing. Then use a lint-free cotton rag (NOT a paper towel as it will leave fibers) and wipe it completely clean, then refill with posi additive first, then oil 2nd. Once oil starts flowing out of the fill hole, you are full.

BTW posi rears need to be serviced every 30k miles or less. I pushed mine to 50k and it was making all sorts of noise when I'd turn at low speed. Flushed out the rear axle and fluid and now it's nice and quiet again.

I'm glad I read these posts, because I'm getting clunking back there on tight corners at low speed, especially if there's a gradient or driveway curb involved. In a very tight turn in a parking garage, there was a bang-bang-bang-bang that I thought meant the end of the differential.

Are you guys saying there is still hope as long as I change the lube and add additive? Does anybody use Amsoil Sliplock? I extracted a few oz. of old gear oil and added Sliplock, but it made no difference, so I guess I'd better drain the diff. Is Royal Purple synthetic okay as a lube? Should I use 75-90? Thanks for any advice.

Oh--I read somewhere that the GM gasket has some sort of defect, maybe an incorrect pattern, that won't let lubricant get to...was it the axles? That doesn't make sense. Anybody know anything about that? Thank you again.