what fluids does everyone recommend for diffs and transfer case

[jumpinjupiter]

Looking to do a fluid change soon on my transfer case and both differentials. Any advice on the process and recommendations for the best fluids.

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[JohnnyO]

You have a 2021 so it may or may not have drain plugs on the diffs. My 2020 does have drain plugs on both but it's something they phased out. Drain plugs are not on the covers but in the body of the diff. If one or both do not have drain plugs, my advice is take it to the Valvoline Quicky Lube where they suck the lube out of the diff with a machine.

If you do have drain plugs, the factory spec is 80w-90 conventional gear lube. This is curious because older Rangers have synthetic factory fill. The only synthetic I found that meets the Ford spec in the owner's manual is Redline 75w-90, p/n 57904. I'm in the process of getting some now from Amazon but at $24 a quart I got some last pay and some more with my next pay. Conventional axle lube costs much less. You do not need limited-slip additive since no Gen 5 Rangers have a limited-slip rear diff. The factory locker is not a limited-slip. The front axle takes a bit over 1 quart and the rear takes a bit less than 2 quarts. Harbor Freight has a hand transfer pump for about $8 that makes filling the diffs and t-case easy-peezy.

I changed mine the first time at 30k and they drained out pretty black, I'm coming up on 90K and will do it again, and at 150k if I have it that long.

The torque specs on the drain and fill plugs is pretty light, like 18-20 ft. lb. and I'd advise using a torque wrench so you don't over-tighten them and strip something. The transfer case is aluminum and the diff covers might be, I'm not sure.

The transfer case calls for something like Ford Transfer Case Fluid but I found that Redline D6 ATF meets the Ford spec in the owner's manual so that is what I used.

 

[Burnt Money]

I have ran conventional gear oil in the past. I currently have Valvoline synthetic in the front and rear. I’m running the Motorcraft ATF in the transfer case that’s recommended in the manual. I’m at 87k miles with probably 10k of them towing. My honest opinion is don’t get caught up in the brands just keep them changed with the proper fluids and weights. I do both differentials and transfer case yearly. I fill all 3 till it spills out of the fill hole.

 

[Frenchy]

Do yourself a favor and open the owner's manual. Once you do that go to the maintenance section that will include specifications for different types of fluids. Check that to find out what's your vehicle calls for. It will help save a lot of time

 

[harringtondav]

If you are considering a syn gear lube, take a look at NEO synthetic gear oil. Meets GL-2 through GL-5 and MIL-L-2105E.
I used it in my old Mercruiser Alpha 1 outdrive. After 25 years the spiral bevel cutter marks were still visible in the wear pattern.

 

[Atxjmy512]

What's the conclusion here - stick with conventional 80W-90 or is synthetic 75 W-90 ok / preferred?

 

[harringtondav]

What's the conclusion here - stick with conventional 80W-90 or is synthetic 75 W-90 ok / preferred?

I'd stay with Ford's 80W-90. Spiral bevel and hypoid gear sets are one of the most stressed. Compression stresses are high in the contact area, and pitting can result from overloading or poor lube.
I prefer full syns everywhere. ASTM D4172 shows superior wear vs mineral lubes.

 

[harringtondav]

If you do have drain plugs, the factory spec is 80w-90 conventional gear lube. This is curious because older Rangers have synthetic factory fill.

Also interesting is Ford specs semi-syn engine oil, even though full syn is proven superior. ...Ford dealers sell their full syn in that viscosity.
I wonder if the no drain plug diffs were some "lifetime gear lube" pipe dream that supported full syn gear oil. I'll go full syn when mine is due.

 

[Atxjmy512]

I’m going to split the difference and go with the amsoil severe gear 80W-90 I saw used in the write up. I hadn’t read that yet when i posted. Little more expensive but I too prefer synthetic. Even with the engine oil - I request the full synthetic.

 

[Cmar]

Yes that recommendation change is weird, it happened over here too. All the oil company service advisory charts used to recommend full synthetic 80W/90 for front and rear diffs, for Ford Ranger 2011- on, then a couple of years ago many of them suddenly changed the recommendation to 80W/90 mineral or semi synthetic???
The Ford manual recommends 80/90 full synth, but ironically the Mazda BT50 manual (until a couple of years ago the Mazda BT50 was a Ranger clone - built in the same factory) Mazda recommended 80W/150 for the rear and 80W/90 for the front!
Ford also recommended 5W/30 oil full synth for the engine, and Mazda recommended anything from 5W/30 to 15W/40 depending on average ambient temperatures for the same engine! (3.2 diesel)
As long as you use a good quality oil, and change it regularly, I don't think for diffs it matters all that much if you use mineral or synthetic. I've had good service from both in the past. If you're going to just leave it in there, then I guess that synthetic might be a better bet.

Ironically many of the diff rebuilders over here actually recommend mineral oil, changed more often, maybe they're just chasing return business.

The transfer case is easy, just Ford Mercon LV or one of it's aftermarket equivalents. I used Valvoline Max Life.

 

[Atxjmy512]

Thanks. My main question was really around 75w or 80w. I know the manual says 80w but I’ve seen a lot of discussion over the years of threads I just read talking about 75w for the synthetic benefits. I’m inclined to stick with the manual but trying to understand whether there’s any risk to going with 75w-90. It just seems easier to get.

 

[Cmar]

I actually used 75W-90 synthetic, myself, the supplier said that it was equivalent to, and could be used in applications which called for 75 or 80W 90. That was 2 years and 20,000 hard Km ago.

 

[5thranger]

I had syn 75/90 but went with Motorcraft 80/90 I got it from Amazon

 

[JohnnyO]

Also interesting is Ford specs semi-syn engine oil, even though full syn is proven superior. ...Ford dealers sell their full syn in that viscosity.
I wonder if the no drain plug diffs were some "lifetime gear lube" pipe dream that supported full syn gear oil. I'll go full syn when mine is due.

I suspect that Ford just wants to push their own brand of oil, which is good enough, but full syn is better.
If memory serves, the manual says to change the diffs and t-case at 150k but if you've ever changed them yourself you'll see that the lube drains out like tar at 30k.
Not machining and adding drain plugs probably saved Ford or Dana $5.

 

[JACKSMYDOG]

For the transfer case I went to the dealer and got the recommended WSS-M2C938-AMERCON LV.

Valvoline 80W90 for both diffs.

Number one rule for all three: ALWAYS remove the fill plugs before the drain plugs, or splitting cases.

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