ATIS

I just drained and replaced my fluid in the 75. I used Royal Purple 75-90 syn with posi additive already in it. No issues, nice and quiet.

Stephen Irons

Axle Lubricant GM Part # 89021671 - Two required
Limited Slip Axle Lubricant Additive - GM Part # 1052358 - One required

Bond007

Thanks Everyone

Clams Canino

Same here.
Noting louder that you DON'T use the additive in Royal Purple.

-W

jim2527

When I did mine I drained, refilled, drove a few miles, drained again and then refilled. You'd be amazed at how dirty the second drain is.

Clams Canino

I had the cover off mine - cleaned it pretty well inside before refilling.

-W

DanielA

I need to add some posi conditioner to my differential. I had the car up on ramps last weekend. It is pretty easy to touch the fill plug, but how can you get a wrench on it? It is a square nut and there does not look to be any room to swing a crescent wrench.

There must be an easy way to do this. Could comeone clue me in?

Clams Canino

You can us a 4pt or 8pt socket easily enough. Or if lucky you can break it free with a crescent and turn it out by hand. I believe it might have a little taper to it.

-W

travelerbob

I'm not sure whitch co. offers it but there is a kit to add a drain plug to the diff. Template shows where to drill and supplies the drill / tap and plug. Price reasonable. May have to Google it. Sounds better than the sucko job.

Super6

When you add these, make sure you put the Limit Slip Axle Lube additive in first. This way the whole contents get in the differential. If you do it the other way around, adding the additive last, the fluid starts to overflow out the opening before all of the additive is in the diff.

The well-known gentlemen from Connecticut, who is one of the premier rebuilders of rears, steering boxes and trailing arms, recommends the GM fluids over the synthetic stuff. FWIW.

Ralphbf

I am a big fan of synthetic oil and grease.
I used conventional oil and GM limited slip treatment.

Ralph

C3 Vette Dude

What is the wait of the GM fluid and cann it be purchased from a local autoparts store like Autozone?

Clams Canino

Chevy parts counter.

-W

Ralphbf

If the question is "What is the weight of the oil for the rear end ",it's 75/90.

And it's available most any where. The additive is about $10.00 at the dealership.
It should take almost 2 quarts. The additive is 4 ounces.

Ralph

C3 Vette Dude

Thanks Ralph. Can it be changed without lifting the car. Can I change it in my garage laying on my back or is it to low to the ground.

Ralphbf

You have to get under the car some how.

I like using ramps they are fast, easy and safe.

You will need a 5/8 8 point or 12 point socket, 4 inch extension and a ratchet.

Plug in it the top right rear of the differential.

And you will have to suck out the old stuff and pump in the new.

Some remove the cover, clean out the crud, replace gasket and reinstall the ten bolt cover. No sucking involved that way.

Ralph

C3 Vette Dude

Thanks again! How did you get that picture of your car on the post?

Ralphbf

Honestly I fumbled through. It was on my 3rd attempt, and I can't really remember.

R~

bouvie1

My question is where do you siphon/fill GM lub/additive. Any pics or location will be appreciated. Thanks bouvie1

Ralphbf

Passenger side, top rear, there is a plug.

Suck it out and fill through the plug hole.

R~