what type differential lube ?

[RATRODKING]

guys,. i have a 1990 k-1500 4x4 with 5.7 v-8.

want to add some differential lube to the front and rear.

what weight lube should i use ? i looked in my hayes and owners manual and couldnt find anything,

i have some 80w-90, is that ok ?

also, want to make sure the front gets the same as the rear.

thanks.

leonard

[CarpenterGuy]

i think the owners manual says the front should use 80w-90 and the back gets 75w-90, but i went with 80w-90 synthetic all around the last time i changed the fluid.

[RATRODKING]

thanks for the info..

leonard

[usmctribe]

i think the owners manual says the front should use 80w-90 and the back gets 75w-90, but i went with 80w-90 synthetic all around the last time i changed the fluid.

You need to be carful with the type of fluid you use. Make sure its what the oweners manual says. I know synthetic sounds better and will last long, but it may do more damage to you differential. I worked on cars at jiffy lube and learned the hard way when i didnt used the correct stuff. You can call your nearest lube center and ask them they are generally very helpful or look at your owners manual.

[1st Synthetics]

You are fine using a 75(80)W-90 or a 75(80)W-110 fluid weather it is conventional or synthetic. The only way you should not use a synthetic is if there is RTV used for the sealant. Silicone is used in synthetic lubricants as an anti-foam agent and will cause a reaction with RTV. The front diff should not have RTV but the rear may.

1988-99 models
Do not use synthetic lubricant in axles using RTV sealant.
Synthetic lubricant will chemically atack RTV sealant.
American Axle has only approved the use of Synthetic
Lubricant 75W-90 GM part no. 12378261, as follows:
a. All 8.6 inch rear axles are compatible.
b. All 9.5 inch rear axles built before mid-February 1998
(RTV sealant used to seal cover pan) are not compatible
c. All 9.5 inch rear axles built after mid-February 1998
(equipped with cover pan & gasket) are compatible.
d. All 10.5 inch rear axles built prior to March 3, 1999 are
compatible if axle shafthub RTV sealer is replaced with GM
gasket part no. 327739.