Hello All,

A certain project of mine has me trying to learn how friction modifiers work, such as (but not limited to) this:



The project is a relative of the 6F5x transaxle that is very tired and has some TCC shudder starting.

Does it add friction to transmission fluid somehow?

I read a few places where they claim that [all friction modifiers make transmission fluid more slippery to solve TCC shudder] . . . so the friction modification is to create LESS friction?

What is this stuff? Like is it a transmission fluid carrier with extra stuff added? . . . or is it special stuff brewed in a cauldron with the blood of a unicorn and tears of a mermaid?

What if someone were to replace all of their transmission fluid with this stuff? Would it shift really really ridiculously firmly while eating its bearings, bushings, and gear faces? (I'm not asking this one because I have done this or want to do this, I'm jut trying to understand what this stuff does in full force to get a better idea of how it affects whatever it is mixed into, kind of like the difference between a bottle of chlorine versus the small amount that many municipal water systems put in their water)

Thanks!

 

My experience is with clutch-type limited slip differentials. In there, friction modifiers are supposed to make the lube more slippery, so the clutches will slip more when you're taking a turn. If you take a sharp enough turn and apply enough drive force, the clutches will still grab, causing judders and tire chirps.

In transmissions, the blocker rings (in a manual) and clutches (in an automatic) all rely on a certain amount of friction to work. In those cases, I would think that you do NOT want to reduce the friction of the lube.

If you have a helical gear type differential, it's also advised against using a friction modifier, as the gears rely on some amount of friction between the teeth to work.

 

Why would you ask this question and what makes you think someone here is smart enough to know what the real answer is?

If you have a converter shudder, if you follow the instructions, it is worth putting in. It just might fix your problem, especially if the converter clutches are grabbing. I have used this stuff in my clients vehicles and have had about an 80% success rate [not scientific]. If it does not work, the converter gets sent out and the shop, that I send my converters to, says there are parts actually worn out. This magic fluid cannot fix worn out parts. There is no snake oil that does.

 

Thanks! That's why I'm here. I've seen some anecdotes that say that a friction modifier makes the fluid more slippery . . . but it doesn't make sense if it is advertised as a cure for slip unless it is attempting to make the grabbiness of clutch shudder less grabby. I'm hoping someone can explain that to me. Maybe there is a logical path between the two.

I've never dealt with friction modifiers except as an additive for limited-slip differentials. In those textbook cases, I use it like the textbook says and then don't have a problem, so voila' it must work . . . like in the textbook. But why and how?

In this case, I'm using in a way that is promised to me by a bright label, but is backed up by little in the way of solid evidence. Anecdotes about using it seem to split 50/50 on results.

 

The entire world, including a few very smart folks that are currently off-planet, has access to FTE. Call me an optimist, but I bet at least a few of them know more than I do on the subject, and maybe one or more of them might see my question and answer. Then I'll know more than I did, and hopefully that new knowledge will help me with my next steps.

Then, later, hopefully someone catches this thread, with the great explanation, and learns something that helps them and/or the world somehow.

That's approximately why I would ask this question and think someone here is smart enough to know what the real answer is. As of this writing, this thread already has 75 views in the 1,452 minutes that it has existed, so that helps my optimism.

I agree, but I still want to know what makes it do what it does.

 

The question was has anyone ever used 100% friction modifier. The tube is 2oz. There is about 18 quarts of ATF in an E4OD. Yeah, I know, give or take, it depends on what you got, but go with me on this. Since there are 32 oz in a quart, that would me you would need to buy 288 of these tubes and at $8 a tube, that is about $2,300, plus tax and shipping.

Now, do you see why I would ask my question? Sure, there are a lot of people on the internet but there is not a one that would ever do this. I am probably the only one that believes there are stupid questions. I was raised never to ask for help. Basically, it forced me to figure it out myself. Sure, it was tough as kid, but it made me research before I finally did ask. I am better off for that.

Friction modifier has been around longer than I have been working on cars [late 70's]. Usually it was in limited slip differentials. They did not have lock up converters back then.

 

We are waaaay down a rabbit hole that I didn't intend to create. Sorry!

Yes, the sixth (or fourth, depending on how follow-up questions are counted) question that I asked in my original post was:

. . . but really it included follow-up questions that clarify the direction of this question:

. . . including that whole long part in parenthesis that mentions not wanting to do this and wanting to understand what this stuff does in full force to get a better idea of how it affects whatever it is mixed into.

So, to more-accurately answer your question:

. . . my answer is:

To offer a hypothetical scenario that will help me to better understand the effects of friction modifiers on automatic transmissions, and because I am an optimist that knows that the entire world, including a few very smart folks that are currently off-planet, have access to FTE, and I bet at least a few of them know more than I do on the subject, and maybe one or more of them might see my question and answer. Then I'll know more than I did, and hopefully that new knowledge will help me with my next steps.

The actual questions that I want to answer seriously are:

We know what coffee is. We know what sugar is. We know what coffee tastes like with a little sugar in it. SFPD Inspector Harry Callahan knows what coffee tastes like with a lot of sugar in it. For my questions above, I know what coffee is, but don't know what the sugar is, and I want to find out.

 

All transmission fluids have an additive package that contains some types of friction modifiers. Type F vs Dexron fluid is one example of two fluids that are very similar except for the additive package and it all depends on the materials that were used in the clutch packs. I remember back when Ford came out with Mercon 5 originally. We had a customer with a Crown Vic or Mercury that had problems with converter shudder. Changing the fluid in the transmission using Mercon 5 fixed the problem. The transmission was never rebuilt and it was fine after that. Later Mercon 5 was reformulated to make it backward compatible with fluids that Ford previously used, Mercon III so I don't know if the friction modifier package was altered in any way or if it was just tested in more applications and found to be ok.

The original stuff had Mercon V in green lettering and it said right on the bottle, "guards against transmission shudder".

 

Right; different ATFs have their own additives already, so you do not want to add anything to them that was designed for gear lube in differentials.

 

This one's designed for automatic transmissions:

 

I don't know about friction modifiers for automatic transmissions. I'm just guessing, but to prevent TCC shudder (slippage), you want it to grip better, so any goop you add to it should increase the friction. This is exactly opposite of how friction modifiers for clutch type differentials should work, whose purpose is to reduce friction, allowing their clutches to slip more.

Even if it does increase friction, this sounds like a band-aid to temporarily fix worn clutches or pumps. This may be what you want, until you can rebuild the transmission.

 

I think you are going about this all wrong. Think about a manual transmission clutch. Do you dump the clutch every time you start moving or shift? Probably not. You engage the clutch smoothly so there is no jerking. This is what is wrong with the converter/differential clutches. You want a smooth engagement, if not, then you will get a shudder.

Is it a band aide? Yeah, probably. As cheap as it is, if it does 'fix' your issue, it does two thing that makes it worth the price of admission. It confirms you need to get a converter or it's something else. My experiences with this product is if it does work, you got 6 month to a year to decide if you want to keep the car and fix it or sell it to some poor sap that will need to replace the converter. The times I used an additive in a differential, it was a 100% fix.

I have also used this additive in transfer cases where there are clutches. That has fixed my clients problem 100% of the time. I'm hero for 'fixing' the turning shudder for dollars verse $10k or more for a transfer case [I work on high end European cars, they tend to be a bit more than your standard domestic vehicle].

 

This is the kind of rabbit hole I can happily follow. Here’s an AI assisted answer that makes as much sense as I’ve ever heard:

Friction modifiers in automatic transmission fluids (ATFs) work by precisely controlling the coefficient of frictionbetween the clutch plates and bands. They are not simply lubricants designed to reduce friction everywhere; instead, they are carefully formulated to allow clutches to slip smoothly during engagement (stopping shudder) while still enabling them to lock up firmly to transmit full power.

How Friction Modifiers Work

Friction modifier molecules are organic chemicals that act as boundary lubrication additives on the metal surfaces inside the transmission.

1. Molecular Structure: A friction modifier molecule has two main parts:
   • Polar Head: This end of the molecule is chemically attracted to the metal surface (like the steel and friction plates) and sticks to it.
     
   • Oil-Soluble Tail: This long hydrocarbon chain extends out into the fluid.
     
2. Boundary Film: These molecules align themselves on the clutch and band surfaces, forming a dense, thin, carpet-like layer. This soft, easily sheared layer is known as a boundary film.
   
   
3. Friction Control: This boundary film is designed to reduce friction and wear during light contact and sliding (dynamic friction), which is critical during a gear change. However, under the heavy pressure applied when a clutch is commanded to fully engage, the fluid film is squeezed out, allowing the clutch materials to contact and create the high friction needed for lockup (static friction).
   

Preventing Clutch Shudder

Clutch shudder—a vibrating or rumbling sensation, especially during torque converter lockup—is caused by a "stick-slip" phenomenon.

• The Problem: Without proper friction modification, the clutch plates might exhibit a static friction value that is much higher than the dynamic friction value. As the clutches start to engage (sliding), the friction is low, but as the sliding speed approaches zero (lockup), the friction suddenly jumps, causing the plates to stick briefly. The tension then overcomes the static friction, causing them to slip again, creating a rapid cycle of sticking and slipping that results in a shudder.
  
• The Friction Modifier Solution: The modifiers are formulated to create a specific friction-vs.-speed profile. They work to ensure the dynamic coefficient of friction (during sliding) is very close to or slightly higher than the static coefficient of friction (at rest).
  

By closing the gap between these two friction values, the transition from sliding to fully engaged is smooth and continuous, effectively eliminating the stick-slip action and thus preventing shudder. This is often described as creating a μ−v (coefficient of friction vs. sliding velocity) curve that is either flat or slightly positive, which correlates to anti-shudder performance.


In essence, friction modifiers in ATF smooth out the transition from the plates sliding past each other to them fully locking up, allowing for a smooth shift without chatter, while still ensuring the ultimate grip is there to transfer full torque.


so as I read the answer, the modifiers change the fluid’s coefficient of friction such that the static and dynamic friction values are more closely aligned such that you don’t get the stick-slip situation that you are currently experiencing.

those modifiers in the original fluid as well as the shear stability of the fluid change and degrade over time with use. New fluid would probably do the same thing as the instant fix in a bottle and is probably a better solution, albeit more work and expense.

 

I tend to agree, that I think I want more friction to solve this, which is why I was surprised to see talk of this stuff decreasing friction.

Waaay too much research today helped me figure this out a little more. Basically let it slip a little more, slowing down more gradually, and then the "stick" part of the cycle is less aggressive therefore less perceptible. Then I came back here, and @meborder's AI explanation filled in a lot of gaps! I hope it's true and not an AI fever dream.

 

This fills in a lot of gaps from a whole bunch of research today. The AI's offered up several explanations, but all seemed half-hearted and incomplete . . . as if they were all the result of the AI's going to Walmart together and reading different sides of the bottles at the same time.