Why no synthetic oil in my Detroit locker?

[Chris142]

I planned on using my leftover Amsoil 75w110 in my Sterling rear axle. It has a Detroit locker in it.

They do not want Synthetic oil in there. Why?
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What kind of oil should I use? Can I use synthetic? Do I need friction additive/modifier?
A quality petroleum/mineral based oil works best in the Detroit Locker units. We do not recommend synthetic oil. Friction additive/modifier is not required.

http://www.eaton.com/Eaton/ProductsServi...tials/index.htm

 

[TC]

How funny....this is the second "Eaton" thread I've come across and responded to tonight, even though I can safely say I don't have a clue as to your answer. (I work at an Eaton plant that manufactures hydraulic valves for airliners and military aircraft.)

This might help answer your question..."The engineer at EATON told me the synthetic oil caused the binding."
http://www.yotatech.com/f31/noise-detroit-truetrack-lsd-72143/
http://www.automotiveforums.com/t922465-rear_diff_oil_burnt_help_.html

 

[Colt45ws]

I have a suspicion that the oils that are causing problems have LSD additive in the oil. Since those are predominately syn they are just blanket warning against syn. Ive read that Eaton has never really tested what syn oils are causing problems and which are not.

 

[tudorart]

You don't need the additive but I got quieter lock ups from using it. No more loud bangs. Most oils do come with it anyway. I would use 140 weight at a minimum. I use Red Line Heavy Shockproof. I tried draining it once right after a rebuild and only 3/4 of the quart came out...the rest was just sitting in there on the teeth and on the inside. When I took it apart again all metal was red on the inside...it was covered. The funny part was that it was mostly where contact occurs.

I would also recommend sticking with a pao or ester type oil. Use the LS additive to top it off if during break-in. That'll keep your temps down. You want that so you don't ruin the gears' hardening treatment from factory. You will also notice how much more quiet it is by using it.

Lubes that have the LS additives, have it on top of the blend and they are usually thicker. What I'm saying is you have the same amount of base stock and EP additive quantity in there. There is no reason an oil LS compatible would fail faster than one that isn't.
You can always go to an 80W for less polymers...that is one thing that may deliver a stouter oil. That also (should) translates to a thinner kinematic viscosity...closer to the base oil's.
So LS and VI additives add artificially to the kinematic viscosity...base oil's being the same. So if anything breaks down, breaks down from that viscosity increase mostly. So you still get your protection by EP and base oil just like in the beginning.
Amsoil is a good choice but I would go higher than 110 (which is the new spec for the old high viscosity SAE90).