Differantial oil

[gooffeyguy]

Is gasket on the rear reusable?

Yes if it's in good shape

 

[swathdiver]

Would you be able to point to written documentation of said change of recommendation?

Yup, my 2012 owners manual shows 75w90 synthetic for both

View attachment 393117

I cannot find the pages where I learned this save one. I might've been in error.

You see Tom's manual is for a Denali and that recommendation coincides with the one in my AllData shop manual for a full time front 4WD axle. It also lists the part time 4x4 axle and says to use 80W90.

We did write about this last year, I just cannot remember or find it. Maybe I was wrong, it certainly seems so according to my AllData.

 

[me51]

Amsoil Severe Gear (SVG) 80W-90 is not a good oil for the front differential, once you turn to AUTO or 4HI you hear a faint humming noise with it. Owner’s Manual just says to use a 80W-90 (GM part number 89021671) so I figured a synthetic oil like for the rear differential would be fine. I just drained it this week and for <1000 miles it looked really terrible (very dark, some very fine residue on the magnetic drain plug). BTW: Rear diff runs SVG 75W-90 without issues.

I found in another forum that GM says to only use conventional/mineral oils in the front axle, so I put in Motul HD 80W-90 which is a conventional/mineral oil. With that the front diff is quiet. When looking at the data sheet the kinematic viscosity value at 40°C of the Amsoil 80W-90 is lower (120 cst) compared to a couple other 80W-90 that are not synthetic (more than 135 cst). The Motul oil has a cst value of 144 cst at 40°C. I figured the viscosity is the same - no matter if synthetic or not - if the grade is the same, but I guess not.

 

[donjetman]

I run Amsoil SVG 75w-90 in the differentials of everything I own, and have owned for the last 16 yrs, without issue including our 07 Denali.
It's in our 41k# Prevost bus/mh pulling another a 10K# trailer, to our 800# EZ-GO gas golf cart. Good stuff.