Changing out the diff cover to a W27 repro. Service manual says to use special limited slip gear oil but doesn't say what weight to use. I have some Lucas 80W-90 that says it's can be used for L.S.diffs. without the use of special additives. I don't want to end up with a bunch of leaky seals so what do you guys recommend.

 

Never heard of leak issues due to the gear oil. Any diff gear oil will work but it needs the limited slip additive to prevent clutch chatter and grabbiness.

 

X2. Many of the bottles of gear oil will say good for posi track rear ends and tries to mislead that you don't need it but you still need the additive.

 

Thanks guys. I picked up some AC/Delco anti-slip additive from a local dealership this morning. Of course it was twice the price as Amazon.

 

Always use the GM additive in a clutch style posi unit. One thing to look for on gear oil is the GL rating. The higher GL rating,the better. The GL rating is basically the shock value of the lube. Probably won't make a lot of difference in a street car but every little bits helps.

 

Mike,
The Lucas gear oil I used says "exceeds API GL-4 and GL-5. I hope that's good.

 

GL 4/5 is normally what you will find on the shelf. There is some lubes available with a higher GL rating if you want to Look. Torco comes to mind.

 

Hit your dealer, I think it’s 2 bottles of posi additive. The guy will know.