Let's Talk Differentials

[TK85]

Going to be changing the diff fluid after motor break in. Lots of info about gear oil weight and what not for the 1st Gen but didn't find much for the 2nd Gen. From what I got was 75w-140 for the rear and 75w-90 in front? Do we need friction modifier added or limited slip gear oil specific? Called up 2 dealerships and got 2 different answers.

 

[Jake17]

Front/Rear axles - WSS-M2C942-A Motorcraft® SAE 75W-85 Premium Synthetic Hypoid Gear Lubricant XY-75W85-QL
http://www.fordservicecontent.com/F...pplement-version-1_su_EN-US-EN-US_10_2016.pdf
Axle(s) and transfer case (4X4 only) fluid
changes or level checks are not required
unless a leak is suspected or the assembly
has been submerged in water. During long
periods of trailer towing with outside
temperatures above 70°F (21°C) or at
wide-open throttle for long periods above
45 mph (72 km/h), change the rear axle
fluid every 30,000 mi (48,000 km), if the
rear axle is filled with non-synthetic fluid.
This interval can be waived and the
150,000 mi (240,000km) service interval
can continue if the rear axle is filled with
75W85 synthetic gear fluid meeting Ford
specification WSS-M2C942-A, part
number XY-75W85-QL, or equivalent. Add
friction modifier XL-3 (EST-M2C118-A) or
equivalent for complete refill of
Traction-Lok rear axles.

 

[Sharkus29]

Going to be changing the diff fluid after motor break in. Lots of info about gear oil weight and what not for the 1st Gen but didn't find much for the 2nd Gen. From what I got was 75w-140 for the rear and 75w-90 in front? Do we need friction modifier added or limited slip gear oil specific? Called up 2 dealerships and got 2 different answers.

Manual says 75w-85 in both front and rear. Depending on what oil you use it should come with friction modifier in it already. I will be using Royal Purple 75W-90 in the front and rear diff's and it comes with friction modifier in it.

 

[zemuron99]

Manual says 75w-85 in both front and rear. Depending on what oil you use it should come with friction modifier in it already. I will be using Royal Purple 75W-90 in the front and rear diff's and it comes with friction modifier in it.

How has this worked out for you, Sharkus? Going to be putting on my Ford Performance diff cover in a few days, looking at the same product. In another search, found a comment that having the friction modifier in the REAR will kill the e-locker, but can't find that comment again.

 

[zemuron99]

Manual says 75w-85 in both front and rear. Depending on what oil you use it should come with friction modifier in it already. I will be using Royal Purple 75W-90 in the front and rear diff's and it comes with friction modifier in it.

How has this worked out for you, Sharkus? Going to be putting on my Ford Performance diff cover in a few days, looking at the same product. In another search, found a comment that having the friction modifier in the REAR will kill the e-locker, but can't find that comment again.

 

[Loufish]

There is no need for friction modifier needed....that's for limited slip diffs using clutch paks in them...no clutch paks in our diffs...
Using 75-90w is fine, or 75-85 for normal use, I'd look at running 75-110 if towing often, heavy....

 

[zemuron99]

Yes, I know the friction modifier isn't needed. But...will having it cause any damage to the rear diff? I'm upgrading slightly to 75W-90 oil, Royal Purple.

 

[jabroni619]

I would not be using oils with friction modifiers in an e-locker or torsen diff when it doesn't call for it. I don't know if it will hurt anything, but i'm pretty sure it won't help and I'd rather not give Ford a reason to void my 100k mile warranty on either of my diffs.

 

[Loufish]

i just installed my rear diff cover also. I took Fords oil standard number and cross referenced to gear oil for Red Line.
If the oil you are looking at to use it should meet Fords spec:
WSS-M2C942-A
w75-85 oil

 

[zemuron99]

Well, did the deed yesterday. Surprised (really, disappointed) at how dirty the oil and diff was on the inside. I know most/all of it is just wearing in metals, but the thought of that gunk circulating around in there unchecked, unfiltered for another 86000+ miles (assuming a change at 100K) is distressing to say the least. I'd purchased both Lucas Oil and Royal Purple gear oils. For now I've filled it with the Lucas product, but I don't really have any experience with them. My plan for now is after 1000 miles or so to drain it to clear out all the gunk the Lucas product as rinsed off the gears then re-fill it with Mobil-1 gear oil. I've had excellent results from their motor oils, hoping this will carry over to their gear oil as well. First pic is the original cover. The white streak at the top/left is where I ran my gloved finger over it to see how much was adhering to the surface. 2nd pic is the original gear lube. A bit hard to see but it's pretty dark, and there are 'streaks' running through it of suspended metals. Right now I only have about 13,500 miles on that lube, and only about 800 of that was while towing. Going to feel much better with 'fresh' oil in there. There's also a fair amount of surface rust on the cover but it appears the o-ring on the gasket was doing its job as the metal where it was is clean. Still, took a fair bit of cleaning to get a good surface on the rear housing for the new gasket to seat against. I did go with a lube-locker gasket which should provide much better sealing as well.

 

[Badgertits]

Well, did the deed yesterday. Surprised (really, disappointed) at how dirty the oil and diff was on the inside. I know most/all of it is just wearing in metals, but the thought of that gunk circulating around in there unchecked, unfiltered for another 86000+ miles (assuming a change at 100K) is distressing to say the least. I'd purchased both Lucas Oil and Royal Purple gear oils. For now I've filled it with the Lucas product, but I don't really have any experience with them. My plan for now is after 1000 miles or so to drain it to clear out all the gunk the Lucas product as rinsed off the gears then re-fill it with Mobil-1 gear oil. I've had excellent results from their motor oils, hoping this will carry over to their gear oil as well.View attachment 129445 View attachment 129446 First pic is the original cover. The white streak at the top/left is where I ran my gloved finger over it to see how much was adhering to the surface. 2nd pic is the original gear lube. A bit hard to see but it's pretty dark, and there are 'streaks' running through it of suspended metals. Right now I only have about 13,500 miles on that lube, and only about 800 of that was while towing. Going to feel much better with 'fresh' oil in there. There's also a fair amount of surface rust on the cover but it appears the o-ring on the gasket was doing its job as the metal where it was is clean. Still, took a fair bit of cleaning to get a good surface on the rear housing for the new gasket to seat against. I did go with a lube-locker gasket which should provide much better sealing as well.

Where did you get the gasket? Any part #?

I have 13.5k miles on my truck was planning on changing the fluid by the 30k mark & also adding a ford performance cover- for the sole reason will make future fluid changes much easier (I installed fumoto valve for the engine oil)

FWIW I’m going w/ Amsoil synthetic 75w90

Everyone’s got their opinions on oils, I’m not going to get into it- I’ll just say I doubt you’ll find anyone who has anything BAD to say bout amsoil (other than price & where to find if)