wildbadbill

I've put a synthetic gear oil in it.....thanks.

lucky131969

Depends on the brand. What are you using, and what do they recommend?

Cybermind

When I changed my diff oil, I refilled it with the OEM GM gear lubricant (which is synthetic). I did also add the recommended additive.

When in doubt, you should add it or you may have to live with rear end noise. I don't think it can hurt.

mjorgensen

Any diff with clutch plates needs a diff additive unless you want the max lock up and can live with a very short lifespan and the noise.

dankhts

add the whale sperm and be done with it

87SAM

As Lucky alluded to, it depends on the brand/type the OP used as some has the additive already in it.

Swt_86

Normally the synthetic lube will have the letters "LS" on the label if they have the limited slip additive already. In theory, you should not have to add the "friction modifier" from GM if you use the "LS" lube. Personally, I didn't take a chance and got the regular synthetic then added the GM stuff.

wildbadbill

thanks guys

Last C5

[QUOTE=Swt_86;1572190157]Normally the synthetic lube will have the letters "LS" on the label if they have the limited slip additive already. In theory, you should not have to add the "friction modifier" from GM if you use the "LS" lube. Personally, I didn't take a chance and got the regular synthetic then added the GM stuff.[/QUO

Careful with Redline, the 75/90 NS means that it does not have the additive in it and the standard Redline 75/90 does have the additive.

Jet-Jock

Is it possible for someone to define the "noise?"

Mike Mercury

I think some believe that just because the oil is "synthetic"... that this alone means it doesn't require any additives. Of course; this is not the case though.

The original GM rear gear lubricant (12378261) did not have the modifier... so you needed to add it.

The newest GM lubricant (89021677) does have the friction modifier already mixed in.

Carcass

Mobil 1 LS75W-90 doesn't need additives.