Eaton recommends running dino lube in differential. Didn't have any on hand for 500 mile change, but had some Amsoil 75-140.
Seems to be running fine so far.
I'm running 35's on 4:56 gears. DD and trails.
If I go dino, would 80-90 be fine?

 

I'm running Royal Purple, I think 75W-90, for over 20k miles no issues. 4.56 gears with 35s and 37s in a DD that sees pretty intensive off road use.


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The only issue I have seen talked about was excess noise, (which may or may not have also caused a performance decrease?) thought to be due to the synthetic oil. But, no one could say why syn would cause the noise and dino would not. Dynatrac posted several times that they have sold thousands of truetracs, and the only customers who ever called them about a problem were the ones running syn. None of the dino guys.

I never tried synthetics, but I ran a front truetrac for 10 years and a rear for 4 years on dino with zero problems.

 

What weight?

 

Nope, I have TrueTracs front and rear, but I run conventional. No noise issues here.

 

I run Amsoil 75-140 syn in front ( trutrac ) and the same in rear diff with ARB locker no issues