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Front and rear differential lube recommendations please.

5K views 4 replies 5 participants last post by  the roadie 
#1 ·
Even though they were checked at a quickie lube place before I bought this vehicle, I'm going to change them out. What would you all recommend for these two differentials front and rear? Brand, weight, specs, etc. I'll also be doing the transfer case but found out the Autotrac II is recommended. Thanks for any input. c good
 
#3 ·
Any good quality 75W-90 is fine. Many of us have gone to full synthetic 75W-90 front and rear. Mobil 1 and Amsoil make two of the most popular choices in here.

If you have the G80 locker rear, you should get one made for limited-slip differentials. This is not critical because:
#1 - You can always add a limited slip additive in whatever you choose, plus;
#2 - There is some debate as to whether the G80 needs an additive anyway, because it is more mechanical in its operation than ones that use the more traditional clutch packs.

Be careful adding an additive to a lubricant that already has it because you can actually make it TOO slippery and it won't lock up properly. For example, Amsoil has it already but Mobil 1 only has it in the 75W-90LS version. (My friend roadie can explain this a million times better than me ... and no matter what we recommend in here we always defer to "WWRD.")

Stick with the AutoTrak II for the transfer case. It is inexpensive, and the transfer case NEEDS changing every 50,000 miles without fail or you risk majour problems.
 
#4 · (Edited)
You have to use a full synthetic gear oil, that is what all modern GM diffs call for. If you want to go ahead and change the transfer case too (easy, it has a drain and fill plug), it ONLY takes Auto Trak II which you can get at the dealer. You can also ask for the LS gear oil at the dealer, which is full synthetic and has a limited slip additive already in it. They may try and tell you the LS gear oil is only for a Corvette, but that's fine because it works just the same. I believe it's only about $8 a quart, unlike the regular GM gear oil which is $30 a qt. Typically you'll need 2 quarts exactly for the rear diff and a little under 2 qts. for the front. The TC also takes 2 qts.
 
#5 ·
I use Mobil1 75W-90LS from Kragen. But then I'm not a fan of the more expensive purple alternatives. If my axle breaks, I just swap it out. :D

As always, read the Owner's Manual first before even consulting trailvoy. It's not 100% full of lies like folks think. :woot: And the fluid requirements are listed.
 
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