Down the Gear Oil rabbit hole again: for Eaton Torsen “upgrade”

[DuckRyder]

Eaton did not design the Truetrac, they acquired it when they acquired Tractech makers of the Detroit Locker and Truetrac.

I strongly suspect this is a legacy recommendation carried forward.

Eatons test for function amounts to putting one wheel on a high traction surface and one on a low traction surface (but not NO traction) and nailing it, If your not sitting there doing one wheel peel it is working.

I really don't even know how you would test this in an instrumented way, I don't think you can do breakaway torque like a clutch type limited slip, I'm willing to listen to suggestions on what might be a valid test other than Eatons.

I'm curious about this shop that wants to use the Amsoil because it has FM and not using FM in a Truetrac is the one thing that there seems to be fairly universal agreement on.

 

[56Cummins]

Dodge 11.5 AAM comes with a torsen from factory. Mopar calls for a synthetic fluid, from everything I have read.

 

[Impatient]

Apparently there is a T2, T2R (with “clutches” of sorts in addition to the Torsen), some OEM versions, the Eaton TruTrac and a PowerTrax GripPro. I delved into each a bit, thinking there might be a solution favoring or at least 100% tolerating some full synthetic fluid. Most all appear to shun FM’s (this is a bit of a generalization), a good portion frown at synthetics in general (another generalization), but none appear to “favor“ synthetics. on the other hand, you’ve seen testimonials from synthetic users. So I’ll keep “pondering” for awhile, no doubt annoying people in the process.

but, i did find this (attached)

 

[Apples]

One year, two weeks later...

Greetings. First post here on BITOG. I found this thread yesterday while poking around for info as I have just had installed last week an EATON Detroit Truetrac helical gear limited slip differential in my 2WD 2016 F150 SuperCrew's 8.8" Super rear axle, along with a 4.09 Richmond Gear ring and pinion. One reason for the axle ratio change is my tire size of a 34 X 10.50 X R17LT all terrain tire. The truck's transmission is the 6R80 six-speed, and the re-gear gives my back the use of my transmission's 6th gear, along with restoring it's 4.17:1 1st gear to as low as is effectively possible for slow-vehicle-speed negotiation of washed out, damaged or otherwise unimproved off-highway routes.

I use the truck as retiree transportation (no weekday commute to work) but it's focus is monthly runs on the interstate up into the southern California high desert to mosey across dirt USFS BLM routes to some of my favorite fishin' holes. Being the truck remains handicapped from the lack of any front axle drivetrain, I study our capabilities carefully when considering certain routes, roads or trails. A man's gotta know his limitations.

The shop that installed this gear set and differential knows of the basic lube requirements or suggestions by EATON for the Truetrac, those being to use an 80W-90 conventional gear oil and one without any friction modifiers. I mentioned this and spoke of my intention to use an 80W-90 after the break-in period when the installer spoke of his general practice for applications like mine of using an 85W-140 for better oil film strength and heat resistance for the 500-mile gear break-in process. To this I agreed and now 220 miles into the break in I have warmed up to the idea of using 85W-140 exclusively, HOWEVER... however I am cursed with a "Split The Difference" vehicle performance mentality to which I can seem to find no cure. I now subject you to this behavior. Forgive me.



Then I read a portion of the letter posted just above in a previous post by the OP:

"Typically, heavier oil weights provide better protection since they leave a heavier film of oil on parts. This provides better lubrication, it also can provide better shock protection. It is worth noting, however, that the heavier the oil film is, the more it will reduce locking effect (or torque bias ratio) of the differential.

Essentially anything that reduces friction in the diff reduces it's locking characteristic. Between 75W90 and 75W140, you probably won't know the difference. But in applications (like FWD cars) that run ATF...

With all of that in mind, I would personally use the 75W140."

Well, then, that does it.

I had already planned to (ask first, but then) blend my own lube for use after the break-in period is complete with a drain and refill using one part Motorcraft SAE 80W-90 Premium Rear Axle Lubricant and one part Mobilube HD Plus Gear Oil 85W-140. If blended 50/50 this may result in a 82.5W-115 gear oil. Sufficient quantities of each are in stock here already.

My concern is with any incompatibility of the two products' additive packages... While I would think this a non issue it seems wise to ask knowledgeable people first.

Axle housing lubricant capacity is 5.5 pints or 2.75 quarts. I wish to install a diff cover that would increase this capacity by .75 quart to total 3.5 quarts.

Thanks for being here. Thanks for taking the time to read through my preface and my question. Cheers! This site is an invaluable resource.

 

[Apples]

I should add that future runs "up the interstate" and into the western states' Mojave desert will include light towing of a 3000 lb, single-axle box trailer-turned camper sized 5' X 5' X 10', hence the nod to perhaps the greater film strength of any heavier gear oil.