I've been looking threw the tech manuals. I can't seem to find what weight oil to put in the rear end. If anyone knows let me know thanks.

 

75w-90

 

its on the first page of the "front and rear axel" section of the FSM

 

And if you have an LSD, you'll need a gear lube intended for use in one or an LSD additive to be used with whatever you bought.

 

Cool thanks for the help. Must have missed it on the first page there.

 

Unless its a S5 rear lsd unit, then you dont have to add any LSD additive. You can use regular GL-5 gear oil since its a viscous unit.

 

what kind of additive do you need for an S4 LSD?

 

what brand of oil is most popular for the diff? is there a specific type or is it just any 75w-90 oil suitable? is it safe to assume that synthetic is the way to go? what of the lsd additive, is there a brand that is preferred for lsd diffs?

 

Yes, synthetic is usually the preferred type for the transmission and differential because the long change interval makes the higher price easier to swallow. However, synthetic makes a lot more difference in the transmission than the differential, so some people just use conventional oil in the differential. I like Red Line, but any of the top name brands would work just fine. I avoid using Mobil One in the transmission because it has been known to eat the synchros, but other than that I am not aware of any brand that is bad.

 

I put redline heavy shockproof in mine

Disclaimer: My rear diff is missing 4-5 half teeth and used to whine like crazy. Heavy shockproof quieted it right down, only a very faint whine now and after 11 auto-x events of hard launches the diff is still holding up great

 

I've seen gear oil at the parts store that they say is good in transfer cases and and race appilications and stuff like that. Is it any good ? I'm talking about the stuff that comes in the tall bottle with the pointed spout.

 

Several brands come in bottles like that. Do you at least remember the color of the bottle?

 

I use AMSOIL Severe Gear 75W90 with the AC delco LSD additive from a GM dealership

 

It was from Advance Autoparts comes in a white bottle. Who makes the additive for the LSD.

 

Thanks. So would I be good just using the redline by itself in my diff or should I use an additive?

 

Castrol or Valvoline maybe? It would probably be better if you just went back to the store and wrote down what they had and then searched for it on the internet. Either that, or use my method, which is to just search on the internet first and order it delivered to your house.

Red Line, Amsoil, GM (AC Delco), Ford (Motorcraft and Racing), Kendall, a bunch of off-brands, and probably a whole lot more that I don't know about. You shouldn't have trouble finding it.

You can use Red Line 75W90 by itself, or you can use Red Line 75W90NS and add the limited slip friction modifier to your liking. Anything from Red Line that has "NS" in the name does not have LSD friction modifiers. You can use the NS oil in the differential without the modifier, but it will cause maximum lock-up, which may increase chatter and decrease the life of the differential and oil.

 

Well I ended up buying Royal Purple gear oil 75w and the additive. I already replaced the old stuff and it all works like a charm.

 

Royal Purple already has friction modifiers, so if you put in additional friction modifiers then the LSD may have difficulty locking up properly.

 

thank you. for direct and straight forward answers. i REALLY appreciate it...