Rear FX4 Differential Fluid

[Montana]

Well, I just checked two seperate locations, the Ford dealer and Napa, and they both said the same thing that I am seeing:

XY-75W-QL - which is the part number OP posted and is apparently NOT 75w-85 as some other threads say they are. The XY-75W-QL is for the rear dif. 1.4qt.
Xy-75W85-QL is listed as the PTU (transfer case) fluid and uses half a quart.

So apparently FORD has some new fluid with it's special additives or they have a chokehold on the actual information for the rear dif in these trucks. Even the image of the fluid is different.



SO, to all those who have changed out their rear dif with 7w-85 or anything else, it's either a guess or incorrect. I'd really love to see what specific manual says and why all the sudden there is this new 75W fluid for a rear dif, because I've NEVER seen it before.

Personally, I hate buying Motorcraft specific fluids because they always do crap like this, but I'm not going to risk it. I'm buying the correct fluids from MC until something like a Haynes manual comes out and specifies something different. Honestly, what it seems like is Ford doing their usual crap and rebranding something to be MC specific when it's not.

Of course, the dealer asked how many miles I have on it and why I wanted to change the "fully synthetic fluid that shouldn't need changed" lol. Whatever dude. Too much evidence to support the initial break in fluid looks pretty awful.

So, thank you for sharing @mavhopefull - this information is correct. Not something I'm willing to risk and the fluids are roughly the same price as all the other gear oil fluids anyways.

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[bbhaag]

Here are the rear differential fluid specs and capacities from the service manual. Hope this helps!

 

[bbhaag]

Also if anyone is interested here is the fluid specs and oil change procedure for the PTU. I can post the procedure for the rear diff as well if anyone is interested. Just let me know.

1. Remove the filling ptu plug.

 

[bgn]

Also if anyone is interested here is the fluid specs and oil change procedure for the PTU. I can post the procedure for the rear diff as well if anyone is interested. Just let me know.

1. Remove the filling ptu plug.

I generally don't like to speak on behalf of folks, but I'll do it here on behalf of folks who service their own vehicles:

Yes, please!

 

[Montana]

Also if anyone is interested here is the fluid specs and oil change procedure for the PTU. I can post the procedure for the rear diff as well if anyone is interested. Just let me know.

1. Remove the filling ptu plug.

Yea I'll speak for everyone when I say

Thank you!

Really no reason to not do both at the same time. I had seen people post the how to's on other threads but no pics. This makes it a lot easier.

Also, in case anyone is curious, it's about $100 for the fluids I went through RockAuto. Locally, like everything else, they wanted almost $20 more each. Hell naw. But hey... $100 every couple years or 30k at most - not a bad investment.

 

[bbhaag]

Alright here is the procedure to drain and fill the rear diff. In the service manual the fluid level check is a different procedure. I can post that to if anyone is interested. Just let me know.

 

[Montana]

Perfect! This thread should be a sticky now.

 

[bbhaag]

Perfect! This thread should be a sticky now.

Glad I could help.

 

[Montana]

Interesting the manual says to remove and then discard the plugs. Anyone know why that is?

 

[MaverickTopGun]

Interesting the manual says to remove and then discard the plugs. Anyone know why that is?

(((( EDIT: I think I'm wrong about it being a Yield Tightening bolt. Looks like it just has a plug that comes with it's own sealer already painted on the thread, so get two cheap Ford-brand plugs for $6 with new sealant coated on there. ))))

Engineers decided there was too much vibration on that diff.
They spec'ed a "Yield Tightening" bolt, which means it locks & seals by actually deforming the threads just a bit, if torqued down precisely right.

Proper tightening torque is mandatory. Use a torque wrench.

Can't use it again since the threads have actually been permanently deformed, although you could if it's not cracking the threads (undamaged) & you applied epoxy or Loctite to the threads, not recommended here because it's easy to foul up the job.

(Plastic Deformation is a permanent set, slightly beyond the yield point of a metal, similar in concept to Stretch Bolts, but the plugs here just use it for sealing & anti-loosening effects.)

When you put a lock-washer under a bolt head, you get a similar effect, in that the washer is crushed (plastic deformation region of the yield curve) to conform, seal, and prevent loosening.

If you ask chat.openai.com (ChatGPT) this question: "Explain how a yield tightened threaded bolt seals." , it's answer is pretty good.

 

[dalola]

Engineers decided there was too much vibration on that diff.
They spec'ed a "Yield Tightening" bolt, which means it locks & seals by actually deforming the threads just a bit, if torqued down precisely right.

Proper tightening torque is mandatory. Use a torque wrench.

Can't use it again since the threads have actually been permanently deformed, although you could if it's not cracking the threads (undamaged) & you applied epoxy or Loctite to the threads, not recommended here because it's easy to foul up the job.

(Plastic Deformation is a permanent set, slightly beyond the yield point of a metal, similar in concept to Stretch Bolts, but the plugs here just use it for sealing & anti-loosening effects.)

When you put a lock-washer under a bolt head, you get a similar effect, in that the washer is crushed (plastic deformation region of the yield curve) to conform, seal, and prevent loosening.

If you ask chat.openai.com (ChatGPT) this question: "Explain how a yield tightened threaded bolt seals." , it's answer is pretty good.

You may well be right, but still seems like an odd application. I'll be doing my PTU & diff at my next oil change, and will look closely at these diff plugs. Many OEM's "require" new parts be applied for certain fluid maintenance locations, such as the plastic engine oil drain plugs on certain late model F150's, the crush washers on most Honda products, etc... Of course most can be reused many times with no adverse effects. The OEM's are just doing CYA. Not saying this is the case here, but I'll be looking close to verify reuse.

 

[Montana]

Engineers decided there was too much vibration on that diff.
They spec'ed a "Yield Tightening" bolt, which means it locks & seals by actually deforming the threads just a bit, if torqued down precisely right.

Proper tightening torque is mandatory. Use a torque wrench.

Can't use it again since the threads have actually been permanently deformed, although you could if it's not cracking the threads (undamaged) & you applied epoxy or Loctite to the threads, not recommended here because it's easy to foul up the job.

(Plastic Deformation is a permanent set, slightly beyond the yield point of a metal, similar in concept to Stretch Bolts, but the plugs here just use it for sealing & anti-loosening effects.)

When you put a lock-washer under a bolt head, you get a similar effect, in that the washer is crushed (plastic deformation region of the yield curve) to conform, seal, and prevent loosening.

If you ask chat.openai.com (ChatGPT) this question: "Explain how a yield tightened threaded bolt seals." , it's answer is pretty good.

That's what I thought, either that or I was assuming it was some sort of rubber gasket that could not be reused.

So, the question remains, is it a FORD specific part and where do I get it? Probably have to wait for a dealer unless someone can find the part number. I don't have time to look at this moment.

Also, I find it interesting the other thread on this topic where someone used the incorrect fluid, didn't mention anything about this - well... not that surprised I guess...

 

[burst710]

Hi all,

I'm getting ready to replace the Front PTU and Rear Differential Fluids on my FX4 Maverick. In reading through some posts I'm finding some conflicting information. So, I called the dealer and these are the correct part numbers. Let me know if you've seen this before.

Front PTU
XY-75W85-QL

• Motorcraft® SAE 75W-85 Premium Synthetic Hypoid Gear Lubricant is an excellent multi-purpose extreme pressure lubricant recommended by Ford Motor Company as meeting warranty requirements. It is recommended for conventional and limited-slip differentials of vehicles which specify a fluid meeting WSS-M2C942-A

Rear Differential
XY-75W-QL - Disconnect Rear Drive Unit Fluid

• Motorcraft® SAE 75W Disconnect Rear Drive Unit Fluid is specifically formulated for Ford disconnect rear drive units with a low offset hypoid gear
• Developed with a lower viscosity to improve axle efficiency and fuel economy
• Motorcraft® SAE 75W Disconnect Rear Drive Unit Fluid is formulated with synthetic base stocks, friction modifiers, antiwear and extreme pressure additives to provide gear protection and smooth clutch operation
• Use only in Ford Disconnect Rear Drive Units
• Do not use in conventional high-offset hypoid gear axles where SAE 75W-85, 75W-90, 80W-90 or 75W-140 is recommended

How many miles do you have ?? im almost to 5k and thinking to do the same then

 

[MaverickTopGun]

Also, I find it interesting the other thread on this topic where someone used the incorrect fluid, didn't mention anything about this - well... not that surprised I guess...

I'd definitely stick to the Motorcraft 75W Disconnect fluid here, since there are clutch packs that require very specific frictional fluid properties to prevent chatter.

Drain, and also the Fill plugs, are very cheap at dealerships, and they likely have them in stock. Order online or give the parts counter
Part #: 6C2Z4N282AA
, two of them.

I might be wrong about them using Yield Tightened threads here. Now that I look at the part, it is coated with a sealer, which also creates thread friction to keep it from loosening. Taking it off scrapes the sealer off the threads, that is probably why they say throw them away.

Nice they have built-in magnets, and still so cheap. Dorman or other parts brands, make this pipe plug, 1/2"-14, but Ford actually sells theirs cheaper, with the sealant and magnet.

Of course most can be reused many times with no adverse effects.

I have cheated a little on some non-resuble parts by putting some RTV sealant, a thin coating, on like 3 threads toward the outside casing side. Seals, & kind of weakly glues it to keep it from loosening (leaking).
I can't recommend that though. Could cause leaks later.

 

[Montana]

I'd definitely stick to the Motorcraft 75W Disconnect fluid here, since there are clutch packs that require very specific frictional fluid properties to prevent chatter.

Drain, and also the Fill plugs, are very cheap at dealerships, and they likely have them in stock. Order online or give the parts counter
Part #: 6C2Z4N282AA
, two of them.

I might be wrong about them using Yield Tightened threads here. Now that I look at the part, it is coated with a sealer, which also creates thread friction to keep it from loosening. Taking it off scrapes the sealer off the threads, that is probably why they say throw them away.

Nice they have built-in magnets, and still so cheap. Dorman or other parts brands, make this pipe plug, 1/2"-14, but Ford actually sells theirs cheaper, with the sealant and magnet.

I have cheated a little on some non-resuble parts by putting some RTV sealant, a thin coating, on like 3 threads toward the outside casing side. Seals, & kind of weakly glues it to keep it from loosening (leaking).
I can't recommend that though. Could cause leaks later.

Yea I got all the correct fluids from Rock Auto. It's pretty rare that a fluid costs more than Amsoil... but this is one of them. Not really fond of having to do this, so hopefully in the future as more info comes out, I can save on the next fluid change.

The dealer did have the drain and fill plugs and as you said, surprisingly cheap. Still, sucks to even have to do this, but whatever, not that big of a deal. I already got them, but I'll update the thread once I pull them and inspect. I suspect FORD is just being overly cautious here and like you said again, it's due to a sealer. If that's the case, the manual should just specify to use a sealer. But that would make too much sense...

I suspect a simple RTV would suffice here? Or just use a PTFE like Teflon paste? Of course, less is better either way.

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