I just bought some Redline 75W-90 Gear Oil to change my Rear Differential Fluid with, but at the store, I saw another bottle of Redline 75W-90NS fluid. It looks like the difference is the NS bottle does not have a friction modifier, and the other one does.

Which one should we use for our rear differentials? I did a search but nothing came up.

Do you have a limited slip differential (I added the TRD LSD to my GS)? If so, you want the friction modifier (I've got a gallon jug 1/2 empty in the garage so I can check the type if needed)... if not, you don't need it.

I have the factory differential, which I believe is not LSD.

Will it hurt to use the friction modifier in the factory differential? I already purchased the fluid, and if having the friction modifier does nothing negative to the factory diff, I woud rather use it than taking it back for an exchange.

Correct, OEM does not have a LSD on the GS.

That I don't know. If I were you, I'd exchange it.

You don't change the diff fluid that often and I'd be concerned the modifier would cause slipping or some other issue. Maybe one of the Lexus tech guys can chip in here.... I'll move this to the Maintenance forum for you.

The NS is used for non limited-slip differentials.

http://www.redlineoil.com/products.htm

I'm going to get redline gear oil for my differential too, and 2 direct quotes from redline

From regular 75w-90: Excellent performance in conventional and limited-slip units.

From 75w-90NS: Street-driven rear-wheel drive cars should use regular Red Line 75W90 or 80W140.

So which one should be used? Sounds like it's the regular one that should be used in rear wheel drives even if it's open diff. Someone please tell us~

From perusing Redline's website, here's what I figured from their somewhat cryptic information:

75W-90NS: synthetic gear oil WITHOUT limited slip differential additive

75W-90: synthetic gear oil WITH the limited slip differential additive (read at the bottom of the page for the additive information)

From this information, looks like you can deduce that what you currently have in hand, 75W-90NS, is perfect for the stock GS rear differential application. For those that have switched your stock non-locking rear differential for a Supra locking differential unit, then you should use the 75W-90 gear oil.

I called Redline, and they said that the 75W-90 is the right oil to use in most differentials, whether open or limited slip.

Friction modifiers decrease the friction and are better for the differential in most cases.

The tech said that the only cases where you would not want friction modifiers in a differential oil is in racing applications where you want the LSD clutches to have more friction or in a transaxle where the transmission is lubricated with the same fluid as the differential.

Hope this helped some people!

Thx a lot!