Need advice on 1997 GMC Sierra fluids/maintenance

[Chris B.]

I'm going to drain and fill my 1997 1500 Sierra's front diff and transfer case and I don't have the owners manual. Does any one know if it takes 80w90 or 75w90? Is there a certain brand of gear oil these trucks prefer? I think the last owner had Valvoline in it. Does it need synthetic and how many quarts of fluid does the front diff take?

Also the transfer case was flushed when I bought it so fluid looks clean but has some very fine flakes in it so I want to flush it again. I just want to confirm it takes Dexron 3. All the bottles at the store say Dex/merc. Is this the same stuff? Is there a certain brand of fluid that is best for this transfer case? How many quarts does the t-case take? And finally what is the size of the allen head fill hole plug? Many thanks!

 

[Trav]

Can you read the tag on the transfer car and get the model? Most take Dex but one doesn't.
Mobil 1 LS 75w90 will work fine. Even if you don't have a LS diff its not a problem it is compatible with both.

 

[147_Grain]

Spec is 80W-90 GL-5 for the differentials. I would go with 80W-90 for conventional and 75W-90 in synthetic. (Synthetic will get you better gas mileage and pay for the cost differential in the long run.)

 

[Chris B.]

Would the front diff have a limited slip? I thought that was just the rear diff?

 

[147_Grain]

Only rear differentials are limited slip.

 

[Turk]

I had one. +1 to all the advise above.

 

[QuietPortage]

Yep. You're good to go. I used Mobil 1 75w-90 in the differentials and Mobil 1 ATF in the transfer case on my old Chevy.

 

[Chris B.]

Ok I called the dealer and gave them the VIN. They said the rear diff is not a locking diff and has no limited slip. So I just add in the straight oil. Would it be ok to use synthetic or just stick with conventional?

Also what is the best brand for DEX III for the transfer case?

 

[QuietPortage]

You can do like I did if you want - M1 gear oil and ATF. Valvoline Maxlife is another good synthetic dex/merc ATF.

 

[Chris B.]

Is the Castrol Dex/Merc any good? It was that or the store brand.

 

[QuietPortage]

Originally Posted By: Chris B.
Is the Castrol Dex/Merc any good? It was that or the store brand.

Sure. The transfer case is a pretty low-demand application anyhow.