IRS DIFF FLUIDS and friction modifier

[Jeff's First FFR]

I am having a hard time determining which FRICTION MODIFIER and gear lube to use. I have the Ford Super 8.8 3.55 center section.
Friction modifier CM19546-A1 OR X3?
Gear lube 75W90 or 75W140?
I read it somewhere but for the life of me can't find it.
Thanks,
Jeff

[rich grsc]

CM19546-A1 for friction plate limited slip, use 75W90 in cars, the 75W140 is more suited to trucks and heavy loads.

[edwardb]

It's listed in the FFR IRS instructions at the end under "Fluids" and are the same Ford lists for the Mustang:

Motorcraft® SAE 75W-85 Synthetic Hypoid Gear Lubricant XY-75W85-QL
Motorcraft® Additive Friction Modifier (U.S.) XL-3 (U.S.)

Both are dealer items from what I've found, which is what I've chosen to do. Others have used other brands for the gear lube, with some discussion about the weight. But I've stuck with the Ford recommendations.

[Jeff's First FFR]

Thank you for your excellent response.
Jeff

[Jeff's First FFR]

Friction Modifier:
XL-3 or
CM19546-A1

What's the diff?

Oh, boy "diff"

[jrcuz]

Hi Jeff, Diff is the differential. Also the fluids edwardb listed are available at dealers but you will pay dealer prices They are cheaper from places like Summit Racing or Amazom.
JR

[Jeff's First FFR]

HI, sorry, I was attempting to make a joke.
I need to know what's different between XL-3 or
CM19546-A1
Which should I use in my Ford Super 8.8 3.55 Limited Slip Differential?

[edwardb]

HI, sorry, I was attempting to make a joke.
I need to know what's different between XL-3 or
CM19546-A1
Which should I use in my Ford Super 8.8 3.55 Limited Slip Differential?

Why the confusion? The info from Factory Five (plus Ford if you look it up) says to use the XL-3 friction modifier. I have no idea what the difference is. But recommend using what they say. If you want to buy the exact products Ford recommends, I actually found the parts counter at my local Ford dealer was the cheapest. $60.49 including tax (checked my records) for two quarts of the Motorcraft XY 75W85 QL diff lube and one 4 ounce bottle of the XL-3 friction modifier. Expensive, yes. Not available at any local part stores. Checked Amazon and was more plus didn't ship quickly. Summit didn't list either one. Like I said before, may be other brands of the diff lube of the same weight that's cheaper. Which guys have said they use. But I chose to stay with the exact products recommended on both builds where I've used the super 8.8 diff.

[Jeff's First FFR]

Thanks Paul,
You are right. Get the right stuff from Ford. Best price too.
Thanks a lot,
Jeff

[jrcuz]

Sorry for the bad info Jeff, prices look like they have changed since I got mine nearly 4 years ago. I reread your post and get the "diff" joke now.
JR

[Avalanche325]

If you're not familiar with friction modifier, you are in for a TREAT!!

It smells real nice. Somewhere between a garbage dump and a sewer.

[Avalanche325]

$10.55 at Amazon.
https://www.amazon.com/Ford-XL-3-Fri...16111858&psc=1

[Tree]

Would the same fluid be used for the 3.73 torsion diff? How about the quantity, is it the full two quarts plus the full 4 oz. bottle of friction modifier?

[nuhale]

Filled my Diff with 80w90 after too much reading on my 8.8 M-4010-A88 3.27 "Lincoln Mk8" LST. Took around 1.8L with 4oz friction modifier from Ford.

I'm sure many like me of the modifier.. WARNING: This stuff stinks. My garage smells awful and really pissed the wife off.

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

[egchewy79]

I put in 1L gear oil plus the additive prior to installing the rear end. Then added 2nd L until fluid started running out of the fill port. ended up being just shy of a full liter.

[rich grsc]

Would the same fluid be used for the 3.73 torsion diff? How about the quantity, is it the full two quarts plus the full 4 oz. bottle of friction modifier?

No friction modifier with a Torsion, it doesn't use clutch plates.

[edwardb]

Would the same fluid be used for the 3.73 torsion diff? How about the quantity, is it the full two quarts plus the full 4 oz. bottle of friction modifier?

No friction modifier with a Torsion, it doesn't use clutch plates.

Agreed the Torsen setup doesn't use clutch plates. I found it interesting that Ford still said to use the XL-3 friction modifier in their fluid specs for the 3.73 Torsen. I didn't question it and that's what I used in mine. Put in the first quart, then the modifier, then filled the rest of the way. The amount required per Ford is 3.2 pints plus the 4 oz of modifier. So slightly less than two full quarts.

Dug a little deeper after doing mine, wondering if it wasn't required or maybe even a problem. On Torsen's website, they address this. Their answer? Yes and no. Yes use it if the mfg recommends it, and based on what they said I'm betting this is why Ford still shows using it. But no it may not be required. This is a partial quote. Complete article is here: https://torsen.com/tbr-lube-friction-modifier/.

"This begs the question of whether or not friction modifier is actually necessary in a Torsen. Like I said earlier, the modifier is beneficial in smoothing out the operations of friction devices. However, because our friction properties are different than that of a clutch plate differential, you might not see the same symptoms of stick-slip behavior that those would. As noted, clutch plate differentials have a distinct tendency to chatter without friction modifier in the oil, and that chattering can become very objectionable. So, the modifier is essentially a requirement.

In a helical gear diff, however, the stick-slip tends to show up as an audible noise, described by some as a “rusty screw” noise, or as a squeak or moan. You tend to hear it in very low-speed turns, when the steering is at or near full-lock. So, you might hear it while maneuvering in a parking lot, or turning the car around in your driveway. This noise is, as I said, just a characteristic of the friction properties, and is normal. But, if you hear it a lot and it annoys you, adding a few ounces of friction modifier to the axle lubricant will almost always eliminate it. So, the bottom line is it’s up to you."