Hi all,
We are just about to change all oil in my transmission, TF231 filter already done.
What oil will I need for my rear end 75/90 80/90 or else? I have a 2.73 rear end, how can I check if I also have a limited slip and need an additive for that?
Thanks all!

 

Stock is 80/90 gear oil. I'd stay with that.
There should be a limited slip tag on the cover bolt if you have that. If not, once you get the cover off you would be able to see the clutch packs in the carrier. If it has posi, yes you need limited slip additive or you'll feel the rear vibrate/chuck on cornering.

On an already existing posi rear this old, I wouldn't use 75/90 as the synthetic oil could be too slippery for the clutch packs.

You can also check for posi by jacking up both wheels of the car, trans in N and rotate tires. If both turn the same direction - posi. If one turns opposite the other? Peg leg - open carrier.

Clean the diff housing of any old gasket material and make sure the mating surfaces for the new gasket are dry. Felpro makes really good gaskets. I use a bit of permatex 2 to ensure there are no leaks.