I have been getting a lot of noise from the rear end of my 02 Denali. Thanks to all the info in this forum I went back and checked my records to find that when I had the dealer service the diff they put the wrong fluid in (80W90 gear lube, no modifiers). They told me that the earlier QS didn't require the synthetic #12378577 but they would look into it to be sure. I very much doubt that this is true but was looking for a little verification. Any info you guys could give me would be very much appreciated. Thanks

No difference between "early" vs. "late".
Fluid #12378577 is quadrasteer specific. As an alternative to the price wanted for the GM brand quad fluid, a creditable member(Butch 02) on the denalitrucks site had explained it better;

"I've talked with the Delphi guy too. He takes GM's stance to use the "special" fluid too. The only thing special about it is the 1.5 bottles of posi additive. GM doesn't like the techs or trust the aftermarket to get the correct blend, so they recommend the premixed stuff. It's only expensive because it's low production volume. It's nothing more than Texaco 75w-90 with 1.5 equivalents of friction modifier (posi additive) and a special color.
(I researched that GM number extensively about 3 years ago and finally got the answers from Texaco.)"

Hey Quadrant;

Can you post the exact specs and volumes of the fluid and the additive, if you have? GM is producing the fluid now, but considering the low sales volume, I am afraid they may decide to discontinue producing the Quadrasteer fluid in the future.

OK, I took my truck to the dealer and got the run around. They told me that in 02 only something called "QS4" got 12378577, all other Sierras including "regular" quadrasteer got straight 75W90 gear oil. I know this is nonsense but I don't have the service manual to beat them over the head with. Does anybody know where I can get one?

Guth1975, from the service manual:

Rear drive axle, all except 9.75" axle is SAE 75W-90 Synthetic Axle Lubricant 12378261 (Canadian P/N 10953455) or equivalent meeting GM specs 9986115

Rear drive axle, 9.75" steerable axle (whats refered to QS4) is Synthetic Axle Lubricant, use ONLY 12378557 (Canadian P/N 88901362)

Ken, I'm pretty sure the Texaco 75W-90 is the Texaco 2276 GM synthetic gear oil 75W-90 GL-4 GL-5 and the capacity of the rear diff holds 3 quarts. I'm not really sure how much those small bottles of friction modifier holds, but the bottles are small. I've read most people use two(2) bottles. Hope that helps and will continue to see if I can find a little more specifics/details for you.

This message has been edited. Last edited by: Quadrant,

I think I found the problem. For some reason, the code in my truck says G80, not G86. I don't know why. I thought that G86 was QS and G80 was the standard. Am I wrong?

I just replaced all of the fluids in the driveline, except motor crankcase, with Royal Purple. No additive is necessary since it is already in there and is a full synthetic. I have it in both diffs and also the transmission when I did the pan and gasket replacement. Technically there is a blend in there since some of the original fluid remains in the torque converter etc. I use Mobil 1 5/30 in the engine.

quote:

Originally posted by Guth1975:
I think I found the problem. For some reason, the code in my truck says G80, not G86. I don't know why. I thought that G86 was QS and G80 was the standard. Am I wrong?

RPO codes:
NYS = 4 wheel steering (Quadrasteer option)
G80 = Axle Positraction Limited Slip
G86 = Axle Limited Slip