'96 Buick Roadmaster differential fluid change

Howdy!

If you're considering a rear diff fluid change, I did mine today and it went really well. Here is what I can share if you're contemplating the same service at home...

I raised the rear of the car and utilized jackstands under the frame to the front of the rear tires. This allowed the rear end to hang down and provide access to the rear cover. I also watched this video prior to undertaking the job so that I knew what to expect...

https://www.youtube.com/watch?v=Gqug6-DXoIs

All of the differential cover bolts were accessible and easy to remove. The threads all had some RTV/goop on them (probably form the last gasket install) so I took some time to clean them up to simplify installation. I ordered a fresh cover from Rock Auto (Dorman brand with magnet, about $20) to have a nice fresh cover on the differential. I also purchased a gasket from Lubelocker (no RTV required). Nice gaskets... I used one of their gaskets on the transmission during the trans service and was super easy to use with no leaks.

I used Lucas 80w-90 gear oil and a limited slip additive. The Lucas comes in narrow bottles which conveniently fit up within the suspension to the fill hole (thank god, since I didn't want to use a hand pump!).

I have no idea if the rear end has ever been serviced. The car is new to me and I'm setting a bseline for all the fluid services. For a 49k mile car that is 27 years old, the old fluid still looked good and the magnet on the cover had minimal debris on it. Just the way I'd want it to look!

If anyone has any questions, pointers or input let me know. Thanks! This was a good way to spend a few hours in the garage on a rainy day.

Did the new gasket you used have the holes in sides to allow fluid flow to the axle tubes?

Like in this Felpro, top and bottom of the pic:

The gasket I used didn't cover or obstruct any oil passages, it merely covered the sealing surfaces of the differential and the cover.

RTV is never required for a gasket and should NEVER be used on a gasket. Need the gasket to stick? There are products available just for that purpose.

Anyways, I just checked out that lubelocker place and if you used part number LLR-G850 you are going to have a bad time. It doesn't have the holes in the sides like the Felpro gasket and the axle bearings are going to be starved for oil.

So which gasket from Lubelocker should be used? The LLR 82BOP? The LLR 82BOP has the indentation on each side which, I suppose, will allow for oil to flow through the two channels on both the left and right side of the rear end housing face?

The one that has corresponding holes, or one with just the outer ring.

Well, I probably did this job twice for no reason but I learned something and I hope it will help others (the second time went faster...).

The lubelocker gasket I initially used (part #LLR-G850) would have worked just fine had I left it all alone. A portion of the gasket may cover about half of the oil passage to the axle but the other half of the oil passage is open and free... There is probably more flow available to the oil than through the tiny rectangular slots on the felpro gasket. When I took it apart you can see on the gasket the half-moon shape caused by covering half of the oil passage (but not covering the whole thing).

I reinstalled everything with a new felpro gasket (I don't like reusing gaskets and the felpro gasket was in stock at the local parts store). No sealant and no leaks.

Hopefully the pictures of the lubelocker gaskets are attached for clarity...

Now you know for sure it's good. Nice work and write up on the process and double check.