Rear FX4 Differential Fluid

[dalola]

The Motorcraft 75W85 gear oil does not have friction modifiers in it... (see pic of label)

That is for the PTU.

The RD is the straight 75W disconnect oil. Refer to the very first post in the thread for part numbers & descriptions of each oil. They are NOT interchangeable.

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[Bob The Builder]

So if I understand correctly, if I do a complete drain and refill (not sure exactly why anyone wouldn't) then I need to use the XL-3 friction modifier with the motorcraft SAE 75W-85 Premium Synthetic Hypoid Gear Lubricant. Am I correct in this?

 

[bgn]

Much like transmission fluid for most cars, you should absolutely run OEM/Motorcraft here.

 

[dalola]

So if I understand correctly, if I do a complete drain and refill (not sure exactly why anyone wouldn't) then I need to use the XL-3 friction modifier with the motorcraft SAE 75W-85 Premium Synthetic Hypoid Gear Lubricant. Am I correct in this?

NO! The PTU does NOT require the additive, as it is direct drive. Only the RD has clutches, thus requires the 75W oil which HAS the additive included.

Again, refer to the first post for clarity.

 

[DoubleR]

That is for the PTU.

The RD is the straight 75W disconnect oil. Refer to the very first post in the thread for part numbers & descriptions of each oil. They are NOT interchangeable.

Understood... If the additive was required, it would be listed in the materials needed. I was just commenting on what BillBillW had replied to me about-
"No. It must have the special additives (friction modifiers) for the clutch packs. Regular gear oil is only good for non-limited slip differentials."
Yes, the RDU fluid does have friction modifiers.

 

[bbhaag]

NO! The PTU does NOT require the additive, as it is direct drive. Only the RD has clutches, thus requires the 75W oil which HAS the additive included.

Again, refer to the first post for clarity.

The service manual states otherwise. I'm not going to get into an argument on whether or not the service manual is the end all be all but if you refer to posts #17 and #18 you will see that the PTU requires the same fluid as the RDU.

 

[dalola]

The service manual states otherwise. I'm not going to get into an argument on whether or not the service manual is the end all be all but if you refer to posts #17 and #18 you will see that the PTU requires the same fluid as the RDU.

That's not what I see in the posts you reference...... The PTU is 75w-85, and the RD is 75w, so, not sure what you are trying to point out?

 

[AltoBlueLariat]

I completed my first RDU oil change on my 22 FX4 Maverick with 23,000 miles using the parts and fluid mentioned in this thread. It was simple to do. Every thing can be reached from just sliding yourself under the truck from the rear.

I found it easiest to lower the spare tire to gain some elbow room and make it easier to refill. I just used a 3/8 inch clear tube with a small funnel on the end to refill. Since it was filled on a level surface until full, before putting the fill plug back in I then pulled the front of the truck onto ramps so the front wheels were about 3 inches off the ground. This allowed a little bit a fluid to drain out so that when the truck is level the fluid level sits a little below the fill plug.

The oil was very dark and the magnetic plug was caked with sludge so I think it was a good thing to do.

 

[JME42]

I completed my first RDU oil change on my 22 FX4 Maverick with 23,000 miles using the parts and fluid mentioned in this thread. It was simple to do. Every thing can be reached from just sliding yourself under the truck from the rear.

I found it easiest to lower the spare tire to gain some elbow room and make it easier to refill. I just used a 3/8 inch clear tube with a small funnel on the end to refill. Since it was filled on a level surface until full, before putting the fill plug back in I then pulled the front of the truck onto ramps so the front wheels were about 3 inches off the ground. This allowed a little bit a fluid to drain out so that when the truck is level the fluid level sits a little below the fill plug.

The oil was very dark and the magnetic plug was caked with sludge so I think it was a good thing to do.

How much fluid did your RDU take? Mine was right at 0.5qt with the vehicle level. That seems to match up with the OPs youtube video but does not match the discussed fill amount others have mentioned.

 

[AltoBlueLariat]

How much fluid did your RDU take? Mine was right at 0.5qt with the vehicle level. That seems to match up with the OPs youtube video but does not match the discussed fill amount others have mentioned.

About 21 ounces, I had about 11 ounces left in quart can.

 

[Sjurgen]

Yes, quite I bit of conflicting info in here. I agree that 75w85 is called for, 75w90 will work and 75w140 in incorrect. But what about finding a cheaper alternative that does not have the friction modifier additive for limited slip applications? the Motorcraft oil does not have this package added to it and I wonder if an oil with it will compromise functionality and/or void warranty.

 

[bgn]

Yes, quite I bit of conflicting info in here. I agree that 75w85 is called for, 75w90 will work and 75w140 in incorrect. But what about finding a cheaper alternative that does not have the friction modifier additive for limited slip applications? the Motorcraft oil does not have this package added to it and I wonder if an oil with it will compromise functionality and/or void warranty.

You can get a bottle delivered to you for around $40 or less. A differential, between parts and labor, is thousands.

Penny wise, pound foolish to use fluid that is not specced.

 

[Sjurgen]

The PTU and rear diff both have clutches with friction plates of some kind so requiring a friction modifier would not be a surprise. But it would be good to find out for sure first.

I am no where near 30k miles but I may change the PTU and rear diff oil early just to do lots of photos and post a how-to. like I did with the engine oil

I seems to me that the PTU does not require friction modifiers because the Motorcraft 75w85 bottle states that a friction modifier may need to be added.

 

[Sjurgen]

You can get a bottle delivered to you for around $40 or less. A differential, between parts and labor, is thousands.

Penny wise, pound foolish to use fluid that is not specced.

A bottle of what? The MC or equivalent without the FM?

 

[bgn]

A bottle of what? The MC or equivalent without the FM?

The fluid specced by Ford for the RDU. I don't know what the other options are, mostly because I don't believe this is the place to save money.

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