i was told by my local Jeep Dealership master tech that it would be fine and a good synthetic has all the molecules needed for clutches....
also i he made the statement why do 18 wheelers say if you run synthetics in their eaton differentials they will give you 500,000 more miles to your warrenty?

 

I've used 75W-90 Mobil 1 w/no additive since my re-ratio (20K miles ago).

75W-140 is pretty thick and can provoke sluggish locker performance in severe cold.

FWIW

 

Synthetics don't work well with the clutch linings. It states very clearly on Auburn's site to not use synthetics. Eaton doesn't recommend synthetics with their clutch style Posi.

Eaton Posi
What kind of oil should I use? Can I use synthetics? Do I need a friction additive/modifier?
Eaton Posi units perform best when using GL4 (or better) mineral/petroleum based gear oil. A four ounce bottle of friction additive/modifier is also necessary for optimum performance.

 

Are you sure that he was talking about the Auburn locker? Or was he referring to the limited slip that Chrysler uses?

In general, synthetics are going to give you better performance in your diffs...but when you add clutches to the gears that are in there, you change the equation. I'd check with the manufacturer of the locker that you have to be 100% sure. The other thing to bear in mind that synthetic can get very spendy if you're changing your diff fluid on a regular basis due to fording water (and resultant contamination by water)

For those of us with stock rigs:

Us Rubicon guys can run Dino gear oil, or synthetic...no additive required. Adding a friciton modifier to oil that's in a diff that doesn't have any clutch packs would be bloody useless anyways.

I think that the Saharas come with limited slip rear diffs, right? That's where you would want to run an additive...but I think that if you elect to run synthetic, you don't require the additive. But don't take my word for it...figure out what sorta doojamahickey is inside your diff and then RTFM!

 

I just walked out of a dealer and I saw on the tech's computer that additive is needed in the rubi diffs and states aswell with 75w140 to use additive!

so I bought 2 bottles(1 per axle)

should I use it?

 

Additive is NOT needed with Rubi diffs.

 

Thanks Dynatrac!

That is what I read here, but since I saw it on the tecs computer at the dealership, makes me wonder.

Since Dynatrac are highly renouned, I will follow youre advice!

 

Come on!! Is it possible the dealer could be that wrong? No, wait; I mean