RDU Fluid changed at 2,000 miles

[KenE]

Changed my RDU & PTU yesterday at 4,100 miles on 2025 Lariet Hybrid AWD. Backed onto ramps for RDU, pulled onto ramps for PTU. RDU was underfilled, oil not really bad looking, magnetic drain plug had lots of metal shavings. My experience similar to others, no surprises. Fill & drain plugs not leaking, but not tightened to specs. PTU - Fill plug was Very tight, drain plug about same tightness as I found on RDU plugs. PTU also underfilled, no noticeable metal shavings, but old fluid had a peculiar smell. Refilling PTU awkward but doable. My Takeway - Both fluids needed changing early on, glad to have done, will likely not repeat until 30k or more miles. I'm 79 next month, hope I can still do it by then when I'm 80+ Lol.

I'm blessed indeed, but crawling around under truck results in tiredness & a little next day soreness. Reminds me I'm not a young man anymore. Thanks!

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[Chops]

I'm blessed indeed, but crawling around under truck results in tiredness & a little next day soreness. Reminds me I'm not a young man anymore. Thanks!

Yep, I understand. It is the getting underneath, getting back up, getting underneath, getting back up etc that gets me. Immediately & next day too. I try to bring all the tools etc with me on my first trip under - but I always seem to forget something or leave it just out of reach!

 

[Aleks]

... but I always seem to forget something or leave it just out of reach!

That's the universe teaching you humility, trust me Id know, I've become very humble over the years.

 

[ListedGuru]

You should be no more worried about the viscosity of 75W-85 than you should be worried about straight 75W. Mavericks use the Dana-Spicer Advantek disconnecting RDU. It is designed to run on a proprietary “ultra low viscosity” lubricant (reports says that it is similar viscosity to 5W-20), because it has 45% less frictional losses than using traditional 90W gear oil.

But Ford decided that it didn't want to use Dana’s recommended thin oil and they wanted to stick with thick oil instead…… which means they would have to test it extensively with with 75W oil to make sure it could handle the thick oil, before sending it out into the world and seeing a ton of warranty expenses from RDU failures.

If there’s any risk from using the wrong oil weight, Ford has already committed that sin.

There is one other factor at play…. Friction modifiers. The 75W has added friction modifiers for the clutch pack to prevent slipping. The 75W-85 does not have the friction modifiers.

On my first edit, I downplayed the friction modifiers as being a non-issue since you don’t have the locking rear differential found in the Tremor, but on second thought, the disconnect for the open differential in the FX4 is still another clutch pack inside of the differential. It’s just that it is a single clutch instead of a dual clutch. The clutch pack in the front PTU works just fine with the 75W-85 without the friction modifiers. Is the rear RDU clutch going to slip without friction modifiers? This becomes an unknown.

single clutch in FX4

Twin clutch RDU in Tremor.

What I do know from personal experience (from limited slip Mustang) is that if there is too much slipping in the clutch pack during heavy use, it will overheat the clutches, glazing their surfaces, necessitating a new clutch pack.

Changed my RDU & PTU yesterday at 4,100 miles on 2025 Lariet Hybrid AWD. Backed onto ramps for RDU, pulled onto ramps for PTU. RDU was underfilled, oil not really bad looking, magnetic drain plug had lots of metal shavings. My experience similar to others, no surprises. Fill & drain plugs not leaking, but not tightened to specs. PTU - Fill plug was Very tight, drain plug about same tightness as I found on RDU plugs. PTU also underfilled, no noticeable metal shavings, but old fluid had a peculiar smell. Refilling PTU awkward but doable. My Takeway - Both fluids needed changing early on, glad to have done, will likely not repeat until 30k or more miles. I'm 79 next month, hope I can still do it by then when I'm 80+ Lol.

Just wondering if you or anyone else on this thread has had any issues with a clunk or thunk noise coming from the rear of your AWD Maverick when slowing down? The noise happens right at the 13 mph mark for a lot of us and it happens 100% of the time now so it seems. The noise magically disappears if I turn off traction control so it's believed this has some to do with the AWD system at around that 13 mph mark when slowing down.

I have a 2025 AWD Hybrid Mav and I'm almost certain the clunk noise wasn't there during my initial test drove or for my first 2-3 months of ownership. Maybe next time your out turn your radio down and listen for any noises when you are slowing down and cross that 13 mph threshold. Here are a couple of threads I started on the issue with a lot of good info in case your interested:

https://www.mavericktruckclub.com/f...the-rear-at-around-13-mph-when-braking.72905/

https://www.mavericktruckclub.com/f...down-braking-at-around-the-13-mph-mark.72957/

 

[KenE]

Yep, I understand. It is the getting underneath, getting back up, getting underneath, getting back up etc that gets me. Immediately & next day too. I try to bring all the tools etc with me on my first trip under - but I always seem to forget something or leave it just out of reach!

Lol! I spend several minutes thinking about & gathering all the tools I believe I'll need, but seldom successful. Then the 'out of reach' scenario gets you.. the good thing is we all need more exercise as we age! This Maverick is a far cry from my 1970 Mav, straight 6 cylinder, heater & AM radio.

 

[KenE]

Just wondering if you or anyone else on this thread has had any issues with a clunk or thunk noise coming from the rear of your AWD Maverick when slowing down? The noise happens right at the 13 mph mark for a lot of us and it happens 100% of the time now so it seems. The noise magically disappears if I turn off traction control so it's believed this has some to do with the AWD system at around that 13 mph mark when slowing down.

I have a 2025 AWD Hybrid Mav and I'm almost certain the clunk noise wasn't there during my initial test drove or for my first 2-3 months of ownership. Maybe next time your out turn your radio down and listen for any noises when you are slowing down and cross that 13 mph threshold. Here are a couple of threads I started on the issue with a lot of good info in case your interested:

https://www.mavericktruckclub.com/f...the-rear-at-around-13-mph-when-braking.72905/

https://www.mavericktruckclub.com/f...down-braking-at-around-the-13-mph-mark.72957/

Honestly haven't noticed the sound you describe but I'll listen closely today when I'm out n about. I hadn't seen the other posts about the Rear End Clunk until now.

 

[Cherokee]

Im changing my RDU and PTU, at my now due engine oil change. 10,000 miles.
I’ll do both again at 50,000
It’s mighty cheap insurance against the hassle of a break down.
Or a failure after my 100,000 mile warranty ends.
At least when I trade it in and some guy who couldn’t afford a new one buys it with 95,000 miles on the clock he’ll have a good chance of another 100,000 miles with less major repairs.

 

[KenE]

Honestly haven't noticed the sound you describe but I'll listen closely today when I'm out n about. I hadn't seen the other posts about the Rear End Clunk until now.

After yesterday's trips I listened intently for any clinking while slowing with brakes lightly engaged, but no sign of a clunk noise from rear. I believe I was Regen braking only until the last few feet? Any chance you're hearing rear friction brakes engage, not rear end clunk??

 

[Geo8866]

Changed my RDU & PTU yesterday at 4,100 miles on 2025 Lariet Hybrid AWD. Backed onto ramps for RDU, pulled onto ramps for PTU. RDU was underfilled, oil not really bad looking, magnetic drain plug had lots of metal shavings. My experience similar to others, no surprises. Fill & drain plugs not leaking, but not tightened to specs. PTU - Fill plug was Very tight, drain plug about same tightness as I found on RDU plugs. PTU also underfilled, no noticeable metal shavings, but old fluid had a peculiar smell. Refilling PTU awkward but doable. My Takeway - Both fluids needed changing early on, glad to have done, will likely not repeat until 30k or more miles. I'm 79 next month, hope I can still do it by then when I'm 80+ Lol.

Just one thing: you said you changed the fluids on ramps. The truck is supposed to be level for this service. You might want to check fluid levels with all four wheels on the ground.

 

[KenE]

Just one thing: you said you changed the fluids on ramps. The truck is supposed to be level for this service. You might want to check fluid levels with all four wheels on the ground.

You're correct, I'll do that soon. I was planning on having all four wheels up at time of changes.. Best laid plans of mice & men.... Lol

 

[ListedGuru]

After yesterday's trips I listened intently for any clinking while slowing with brakes lightly engaged, but no sign of a clunk noise from rear. I believe I was Regen braking only until the last few feet? Any chance you're hearing rear friction brakes engage, not rear end clunk??

No I'm pretty sure it's not the rear friction brakes engaging and the clunk is usually pretty loud and you can feel it too. I know of one person who had to have their RDU replaced and that fixed their clunk issue but I guess we'll see what happens going forward. Honestly I'm not looking forward to taking it into the dealer but I guess I may have to. I am glad to hear that your not hearing a clunk though

 

[KenE]

No I'm pretty sure it's not the rear friction brakes engaging and the clunk is usually pretty loud and you can feel it too. I know of one person who had to have their RDU replaced and that fixed their clunk issue but I guess we'll see what happens going forward. Honestly I'm not looking forward to taking it into the dealer but I guess I may have to. I am glad to hear that your not hearing a clunk though

I didn't really think it was friction brakes, but threw that out as a remote potential cause. Sorry you're having this problem, and hopefully if RDU is defective your replacement unit is A+ looking forward. Will be watching for resolution.

 

[JohnCondren1933]

That 75W85 is for the PTU its cheap and everyone makes a version.

The RDU uses a proprietary 75W??? bottle you see that only Motocraft sells for almost double the 75W85 & evrryone else says "no can do".

Someone on the forum has been using 75W90 Royal Purple in the RDU for a couple years with no problem, I guess we will know if they are right after 150k miles if Ford Motocraft 75W??? was really magic fluid noone else can copy or not -- if everyone else RDU on Magic Motocraft 75W??? fluid is going strong while the 75W90 Purplr Power RDUs have shit the bed⁰ .

Honestly? Probably ok with 75W85 but now Ford will likely not honor warranty repairs on the RDU because "not using the official Ford spec 75W??? fluid"

& in case there's a question the ??? is my sarcasm for Ford's magic fairydust in the official fluid, or probably more like Dana's magic fairy dust since Im sure Dana is getting kickbacks on every bottle of magic Motocraft RDU sold.

I have 2 bottles of magic Motorcraft 75W rdu fluid I will use those up and next year if I haven't heard of RDUs blowing up on 75W90 I will probably just switch to either Purple Power or Amsoil 75W90 for the RDU.

I have been engineering manufacturing automation for Tier 1 automotive suppliers for 15 years, some of these auto mags piss me off with articles like "Dana 1st developed the 75W proprietary fluid & then developed the RDU around the fluid" bullshit! Dana does not engineer or formulate any fluids its the valvolines & mobile1 doing that & 1 of them probably propositioned Dana "hey we made this magic 75W fluid with xxx properties, it you develop an RDU for it well give you a kickback on every bottle sold, since Ford Motocraft will have no choice but to buy the fluid from us at monopoly prices".

Motocraft doesn't formulate anything, they bulk buy from contracted formulation plants into red bottles & distribute it as official Ford bottles. Ford has basically implied they will only honor warranties if using official 75W??? noone else sells, & it appears every other firm is going along with the charade so they can clear the way for sweetheart deals too.

Ok now I'm worried...

I did both PTU/ RDU a few weeks ago...

But the dealer gave me the same stuff for both. Doesn't match the RDU bottle in your post.

Opinions or explanations anyone?
I'm in Canada if that matters.

 

[Cherokee]

Im changing my RDU and PTU, at my now due engine oil change. 10,000 miles.
I’ll do both again at 50,000
It’s mighty cheap insurance against the hassle of a break down.
Or a failure after my 100,000 mile warranty ends.
At least when I trade it in and some guy who couldn’t afford a new one buys it with 95,000 miles on the clock he’ll have a good chance of another 100,000 miles with less major repairs.

RDU and PTU fluids were correctly filled and the fluids will stay until 50,000 miles.
Fluid was a bit darker but as we all should know you can’t judge a fluid by color.

I was expecting a low fill level and dirty fluids from all I’ve read in here.
Not so in my case.

 

[ListedGuru]

RDU and PTU fluids were correctly filled and the fluids will stay until 50,000 miles.
Fluid was a bit darker but as we all should know you can’t judge a fluid by color.

I was expecting a low fill level and dirty fluids from all I’ve read in here.
Not so in my case.

Glad to hear your RDU and PTU fluid levels were correct. So I assume you changed the RDU and PTU fluids yourself?

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