75w85 rear differential gear oil what are you using

[Ducati1098]

I read somewhere that the limited slip additive is not good for the E-lockers.
The additive seems to be in all of them already. Any thoughts?

The additive isn’t going to harm anything at all.

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[Winds of Change]

Thanks. I am going with the 75w140 that's been talked about on here. They all just seem to have it already added. I was looking and the Valvoline synthetic. It has a rather large price difference between quart and gallon. Like half the price. I need to double check to see if I am missing something.

 

[Fonz54]

Just me, but as Dana recommends 75W-140, I would run 75W-140 in the rear and is something thinner is desired in the front, then 75W-110.

Why not run 75W-140 in the Front? That is what Dana recommends for the front and the rear.

 

[CarbonSteel]

Why not run 75W-140 in the Front? That is what Dana recommends for the front and the rear.

Nothing wrong with that, but I had 75W-110 and the front never sees the use the rear does so 75W-110 is more than adequate; 75W-140 even more so.

 

[Pokey_Cacti]

Someone with more experience can chime in if I cite something in error; please correct this. iirc, GL-5 is for hypoid gears, and the wide-weight-range synthetic (e.g., 75W-140) is GL-4, not GL-5, which could be a problem. That's why I'm particular about where I run it, even though I'd prefer to run it because of the extended viscosity stability (e.g., wide weight range). Need to pick apart the Motorcraft diff gear oil spec to see what that says about this...

 

[crenca]

Someone with more experience can chime in if I cite something in error; please correct this. iirc, GL-5 is for hypoid gears, and the wide-weight-range synthetic (e.g., 75W-140) is GL-4, not GL-5, which could be a problem. That's why I'm particular about where I run it, even though I'd prefer to run it because of the extended viscosity stability (e.g., wide weight range). Need to pick apart the Motorcraft diff gear oil spec to see what that says about this...

Here is a basic explanation:

https://blog.amsoil.com/the-difference-between-gl-4-and-gl-5-gear-oil/

I went with the Valvoline Full Synthetic 75w-140 that was available at Walmart, which meets the "higher duty" GL-5 spec

 

[box986]

So the consensus is 75W-110 in the front & 75W-140 in the rear? (I assume the front never gets as hot as the rear, even on extended highway driving?) Correct me if I am wrong, but the front diff will get just as hot in 2H or 4H on highway driving? Thanks

 

[crenca]

Correct me if I am wrong, but the front diff will get just as hot in 2H or 4H on highway driving? Thanks

Friction, caused by speed and load (torque) cause the diff to heat up. This means the rear diff is usually the more stressed component in that it is bearing load (particularly towing) at speed most all the time. When the front has torque through it, it is usually at lower speeds (e.g. offroad). Even if you use 4A in normal use (as I do) and thus applying significant torque in the lower gears, once you get to cruising speed (in town or on interstate) the diff is disengaged (but still spinning of course).

I don't know if there is a "consensus" for splitting gear oil wieghts betwen front and rear. Most of us use the same (in my case 75w-140) in both diffs. I think @CarbonSteel split it more for the reason he had some 75W-110 he wanted to use up and it made more sense to put the lighter weight in the front because it is the less stressed diff...

 

[the poacher]

I use the Amsoil 75w-140 in the rear and their 75w-110 up front. Works great and no issues.

 

[Brian_B]

Front diff is spinning all the time - even on models with the FAD, you still have one axle connected. It just isn't pushing any power unless you are in 4WD, it just freewheels. Torque on the gears will generate more heat, but the bearings and such are spinning at the same speed no matter what.

That said, as far as how that impacts oil selection - I dunno. I did 75w140 in both just so I wouldn't have to buy two different oils. For the m190 that maybe thicker than recommended, but if my m190 implodes and I have to upgrade it won't exactly make me cry too much - and the last time I changed the fluid the 75w140 looked nearly brand new with almost no wear material at all.

If in doubt, follow the Ford Manual though. 80W90 in front for mortal Broncos, 75W85 for Raptors (I dunno why the difference between regular/Raptor and not m190/m210). And 75W85 for all Broncos in the rear.

 

[CarbonSteel]

So the consensus is 75W-110 in the front & 75W-140 in the rear? (I assume the front never gets as hot as the rear, even on extended highway driving?) Correct me if I am wrong, but the front diff will get just as hot in 2H or 4H on highway driving? Thanks

Use 75W-140 in both. I used 75W-110 in the front because I had it. When I run out, I will be running 75W-140 in both.

 

[box986]

I use the Amsoil 75w-40 in the rear and their 75w-110 up front. Works great and no issues.

I think you meant 75W-140 in the rear

 

[the poacher]

I think you meant 75W-140 in the rear

Ha, thank you for catching that mistake. I did indeed mean to write 75W-140. I have since corrected it.

 

[Nibroc99]

Ao, my key rakeaway from this whole thread is, use 75w-140 gear oil in the rear diff instead of the 75w-85, since Ford only used that oil to safe tenths of an MPG on gas mileage? About to do my rear diff in the next day or two and just crossing my T's before I dot my... buys. (That sounded better in my head. Trying to figure out the best thing to buy right now. Lol)

 

[crenca]

Ao, my key rakeaway from this whole thread is, use 75w-140 gear oil in the rear diff instead of the 75w-85, since Ford only used that oil to safe tenths of an MPG on gas mileage?

I think that is it. Would 75-85 be good enough if after it breaks down after high temperature excursions (from towing, heavy off-road use, etc.) you change it out? Probably...

Does 75w-140 give you an extra bit of headroom and less concern with hard use in exchange for perhaps a 1/10 less MPG? Probably...

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