2000 Tahoe, I had to change my axle seals. That went fine but my question is on the fluid, I know it's 75W-90 synthetic but on these is a friction modifier needed? I've had to use this on similar sure grip / Positraction before and saw no mention of it in anything I've looked at.

 

I used Mobil 1 75w90 in my 1999 Silverado's G80 differential without problem for the 23 years we had it. I would still be using it if the truck had not been stolen in early May.

 

I have been told that the GM synthetic purple limited slip lube ( made by Union 76) is the best available.

 

Well, Phillips 66, which acquired Union 76 around 2000, has always been known for their premium lubricants, greases and motor oils. Depending on the area of the country one is in, finding a Phillips 66 branded or related branded product can be extremely difficult to find.

Mobil 1 products, however, can be found just about everywhere. Now I am not saying that Mobil 1 branded products are better than Phillips 66 or any other major branded product, they are just easier to find. Same thing with Valvoline products - they are everywhere.

 

The GM fluid I was referring to is the one sold at the dealer with a GM part number. I don't know who makes it now.

 

I ended up using a Valvoline synthetic from NAPA. The diff didn't look ike a sure grip with clutch plates so I don't think a friction modifier was needed.

 

Yes the positraction lube is required. A DUI driver wrecked my FLorida GMT400 in april. I now have a 1999 model chevy silverado.
I like the LM7 power, totally aint feeling the lack of squarbody vibes.

I used the Royal Purple(which claims it has the friction mod in it, Haynes says that doesnt count/sister is dating a GM *** chevrolet body tech, he says their service info is to add the friction modiifier.

So...
A guy on the internet, heard from someone ya might not know or ever meet, that the info is right.....

anyways, Heres a quick list of the stuff I use every 30-40,000 miles.
Royal Purple gear oil 75-90 Royal Purple 75-90
Heres the additive, Lubegard Limited Slip 4oz.