Front End Differential Fuid change

[jaesto]

I want to change the front end differential fluid and put Mobil 1 75W-90.
I put a friction modifier when I changed the rear differential.
Is this modifier required for the front end also.

 

[tower]

No

 

[E.B. Cornburner]

If you haven't already done the fluid change, I'd highly suggest using 75w140 instead of 90. Use a quality full synthetic oil like you mentioned.

I've been talking with a guy who specializes in 4x4 drivelines, and he told me that every one that he rebuilds gets 75w140 synthetic gear oil. He saw no point other than cost savings as to why the manufacturers use 140 weight in the rear, but conventional non-synthetic 80w90 oil in the front. Or we thought it might be for warranty issues...Since the rear end works harder usually, it'd be more prone to failure, so a better quality lube was used, but deemed unnecessary in the front.

All I know is he has never had a lube related failure after switching the front diff out to 75w140 synthetic.

That's what mine's gonna get when I do them. I already have my Schaeffer's 75w140 sitting on the shelf waiting for me to get motivated.

 

[tower]

I agree that you should use a quality full synthetic (I use Mobile 1) but what benefit is there in running a 140 weight oil? The rear needs it because you can go 109 up on the highway and I am sure the rear end get hot but you should not be doing that in 4wheel drive (for more reasons the just oil weight).

I sure it would not hurt anything (might make it work a little harder) but don't know about it being "better".

 

[E.B. Cornburner]

The front differential is turning no matter if you're in 4WD or not. There's no disconnect on these like there are on other 4WD SUVs.

When you're talking about synthetic oils, there's still a drastic difference in cold thickness between even a 140 weight synthetic and a 90 weight conventional. You'll still have less rolling resistance with 140 synthetic than you would with any conventional gear oil.

 

[tower]

There is a big difference between turning and being powered, like you said the rear works harder (gets much hotter).

Like I said I doubt it would hurt any thing but I can see no benefit in running 140, but to say that anyone was trying to save money because they use 75w90 is a little silly.

We could run 5w60 oil in the X but what would be the point.

I have run viscosity's other then the recommended but always with good reason not just because "it's bigger so it must be better".

 

[E.B. Cornburner]

I think you misunderstood me when I mentioned the cost savings of using a 90 weight oil.

I was talking about the factory fill fluids. If you have the tow package, it gets 75w140 synthetic oil in the rear end, but 80w90 conventional oil in the front.

Since there's no real point in running two different viscosities for the front and rear end, it's just simpler to run 140 in both.

 

[TCP]

I just finished replacing both front and rear diff fuilds today. One of my customers works at a Ford Motor co. research and engineering for power train for suv and trucks. He told me to use the full synth. 70-140w and friction modifier in both.

 

[IZwack]

I just finished replacing both front and rear diff fuilds today. One of my customers works at a Ford Motor co. research and engineering for power train for suv and trucks. He told me to use the full synth. 70-140w and friction modifier in both .

He probably just wants you to toss more of your money towards Ford .

Seriously though, ask him what friction modifier going to do in a differential that is clutch-less? If there is going to be any major "slipping" in an open differential (like there is in a limited slip) , then there are bigger problems to deal with than the fluid additive. There is a bit of sliding friction in any gear contact (especially the helical cut gears) but I would think the synthetic gear oil would more than cover that department.

 

[TCP]

If Modifiers don't work then why did Ford start using them in the first place, I'm sure they must have seen some benefit to it besides just trying to sell a few 4oz bottles someone.

 

[IZwack]

Well they do "work" when there is a limited slip clutch system -- or else the gear oil's properties are such that when the clutch need to slip against each other like during a turn, it does so in a manner that results in a chattering sound. However, the front differential is "open" and therefore there are no noisy clutch discs to take are of.

 

[E.B. Cornburner]

Limited Slip additive is only required in a limited slip differential. Your front differential does not have a limited slip clutch, so it's not necessary. Adding it will accomplish nothing.

Lots of the full-synthetic gear oils have friction modifiers already added to them, so even in a limited slip rear, an additional friction modifier additive may be unnecessary. I know Amsoil, and if I remember correctly, Mobil 1 have friction modifiers in them already. They will specify on the bottle if they're friction modified for limited slip use.

 

[Thelt]

I had mine done at Grease Monkey a while back and it has not given any problems. It did not cost much as I remember although I am sure more than doing it yourself.