Hmm, won't let me upload a pic right now for some reason, but just checked the online Ford manual and yes you do need additive for RDU fluid changes. Requires "Motorcraft Torque Vectoring RDU Gear Oil Additive", p/n XL-19.

 

OK, I am going crazy trying to find this on the online manual. I can't find it and must be looking in the wrong place. Would you mind posting a link? I think others may be interested as well. Or I might be the only idiot, either way, it would be appreciated.

 

Are you talking about the ring/pinion housing or the clutch packs? From what I've read in the ford svc. manual there's no way to change the lubricant in the clutch packs.

Here's an interesting piece from AW about the Porsche PDK clutches:
the oil-soaked wet-clutches don’t overheat or wear out under pressure. That’s how Porsche avoids damaging parts with launch control. Rev the engine to a high-power point and slip the clutches to get maximum torque to the wheels without spinning them. It’s stunningly effective.

Read more: What is a Porsche PDK transmission and how does PDK work?

 

Just to confirm, do we need to add a additive when doing a RDU fluid change? Its seems the general consensus is it requires it, but I don't see any mention of it in the RS manual.


View attachment 170130

From Ford:

The rear drive unit stores fluid in three separate chambers.
• Rear drive unit differential housing
• Left clutch pack housing
• Right clutch pack housing
The rear drive unit differential housing is filled with Hypoid oil Ford 75W 85 plus 5% Lubrizol FM6179 to lubricate the differential and to actuate the multi plate clutch packs.
NOTE: The clutch pack hydraulic fluid can not be replaced.
The clutches are wet-running multi-plate clutches with a carbon lining and are immersed in Pentison CMF11S 275 ml hydraulic fluid. Carbon is used on the clutches as it has the best properties in terms of power density and NVH (noise, vibration and harshness) performance.
Modulation of the multi-plate clutch locking torque is performed by means of a hydraulic pressure that acts directly on the plate assembly via a piston.

 

From Ford:

The rear drive unit stores fluid in three separate chambers.
• Rear drive unit differential housing
• Left clutch pack housing
• Right clutch pack housing
The rear drive unit differential housing is filled with Hypoid oil Ford 75W 85 plus 5% Lubrizol FM6179 to lubricate the differential and to actuate the multi plate clutch packs.
NOTE: The clutch pack hydraulic fluid can not be replaced.
The clutches are wet-running multi-plate clutches with a carbon lining and are immersed in Pentison CMF11S 275 ml hydraulic fluid. Carbon is used on the clutches as it has the best properties in terms of power density and NVH (noise, vibration and harshness) performance.
Modulation of the multi-plate clutch locking torque is performed by means of a hydraulic pressure that acts directly on the plate assembly via a piston.

I just reread this and if it's a cut n' paste from Ford it is incorrect. The diff fluid plays not part in the multi-plate clutch plate actuation.

 

Ya I was specifically talking about the ring and pinion not the clutch packs. Motorcraft Torque Vectoring RDU Gear Oil Additive", p/n XL-19 it is. Thanks everybody.

 

Yes I just went through this. Don't do the Motorcraft route. Redline has a rear diff fluid for our cars now. It will be cheaper and better to go with Redline. The additive and fluid is 40 bucks vs the 20 dollars for Redline.

https://www.redlineoil.com/product.aspx?pid=40&pcid=4


I have changed my diff fluid with the Redline a few weeks ago.

 

Do we need to run the Ford Torque Vectoring additive? It says from the redline site, "Contains additional friction modifiers for suitablity with clutch-type limited slip differentials - for most LSDs, no additional friction modifiers are required"

 

So for a daily driver no track days and just occasional spirited driving what is the change interval on this fluid?

 

Technically when prompted by the computer via the screen between the tach and speedo, although i haven't heard of anyone report the message yet. Ford says that extended track use will require a change eventually but it is up to the computer to determine when that is required.

 

So, from this thread, I gather that my leaking RDU is only leaking the ring/pinion fluid, and NOT the clutch pack fluid, correct?

I'll be taking in to the dealer soon, but wanted to make sure that I knew what to expect in terms of downtime and service.

 

From what people have been saying, anything that is more than just a quick look at it with the RDU will just be a replacement. Hopefully not the case with your car.

 

Just so i am clear...i want to change my RDU fluid and in the RS booklet they gave use with the owners manual it just says 75w-140 and its 30oz. I am going to use Amsoil 75w-140 which has limited Slip additive in it all ready. So i should be good right???

 

No, do not put that in your RDU. The RDU should use 75w-85 with a friction modifier. I think you are confusing it with the PTU which would require the 75w-140 which to my knowledge does not need a friction modifier.

 

It says that the diff fluid is what is "actuating" the piston that controls the compression and de-compression of the plates. I guess think of it as how your clutch works with fluid pushing the fork that pushes the TOB to release the clutch from the flywheel.

 

While we're on the subject...
a) Do I trust the computer to tell me the RDU oil should be replaced even if I *know* I've put more than 500 track miles on the vehicle?
b) Is this a reasonable DIY job for somone who has never touched a gear or tranny fluid job *but* has done tons of brake and suspension work? (i.e. capable of working on cars generally)

 

So... almost a month later and nothing? I added another 200-250 track miles for a total of 600-700 or so. Add in almost 100 autocross runs and I would have thought I'd get the service light for it. (I *did* get the engine oil change light on the way home from that track weekend at 8500 miles).

 

Necro bump!

So I'm planning on doing the RDU fluid swap for kicks and just noticed this whole additive deal. I see on the manual that it is a 1:1 container ratio (1 bottle of fluid to 1 bottle of additive). What I'm wondering is, how exactly do I mix the two? Should I just fill the RDU with the fluid then the additive and just let itself mix? should I pour both bottles into a container, mix, then put the whole concoction into the RDU all together?

And yes, I am aware that there is a redline equivalent that does not require any additives, but this time around, I would like to stick with motorcraft.

 

Best to mix and then add to the rdu. There's an hydraulic pump in there and it may not appreciate a gut full of additive only until the gears get a chance to mix it together.

Ciao

 

I'm old but there is a saying if it "aint" broke don't fix it...jmho....

 

not sure if this has been discussed already...but i see panda motorworks has an updated redline RDU gear oil that has the friction modifier mixed already (meets all ford specs). i tried to order the xl-19 through tasca and 1 month later no shipment. so i'm gonna give this stuff a try.

Redline Upgraded RDU Fluid- Red LIne

Buy Redline Upgraded RDU Fluid for only $23.53

www.pandamotorworks.com

 

I got mine (XL-19) from Summit a few weeks ago. Came in a few days. Was surprised how fast it got here (in SoCal).

 

You can use Amsoil Slip Lock as additive in the PTU and in the RDU. What it does is add long chain friction modifiers which increase shear resistance and make the gear oil a little better. This works for true limited slip diffs (with clutches) as well as fake ones (helical gears) but more generally for any diff or transfer box, or any gearbox which does not have synchros, i.e. dogboxes- not ours.

I also added some Liquimoly MoS2 anti-friction (1/2 of each additive, in both the PTU and RDU) and I feel good about it 😇

That second one is only for pure gears (diffs without clutches, and gearboxes without synchros) - it’s so slippery those friction-based devices would not work well.

The PTU and the RDU (the part where we change the oil anyway) are just CWP’s (crown-wheel-and-pinion) so it’s open season for additives of all kinds.

As for the oil I use Amsoil Severe Gear on both, in Ford’s recommended viscosities. So far no issue, and I never had any AWD errors due to overheating so far.