# Coefficient of Friction Values

#### BMW Dom

is there any way we can determine the required coefficient of friction required in a transmission?
Is there a way to see what kind of coefficient of friction an ATF provides?
Do we have any info on the coefficient of friction values?
What makes different transmissions require different frictional values in a fluid? Or are they all the same?

This is my latest enigma.

#### CKN

is there any way we can determine the required coefficient of friction required in a transmission?
Is there a way to see what kind of coefficient of friction an ATF provides?
Do we have any info on the coefficient of friction values?
What makes different transmissions require different frictional values in a fluid? Or are they all the same?

This is my latest enigma.

I just need to ask a couple of questions -

Why is this an "enigma" for you? Verses just following the owners manual? OR using what's recommended or if an older vehicle-what's compatible?

OR-is this thread just really a "Thick vs. Thin" thread-TRANMISSION FLUID VERSION"?

#### Jetronic

is there any way we can determine the required coefficient of friction required in a transmission?
Is there a way to see what kind of coefficient of friction an ATF provides?
Do we have any info on the coefficient of friction values?
What makes different transmissions require different frictional values in a fluid? Or are they all the same?

This is my latest enigma.

The coefficient of friction is likely changing as the speed differential changes between the mating parts, and it could go either up as speed drops, or down.

#### MolaKule

Staff member
CVT or Step-Shift?

Google these: LICENTIATE THESIS, Department of Engineering Sciences and Mathematics Division of Machine Elements, Wear Behavior of Wet Clutches, by Niklas Lingesten

and

Frictional Properties of Automatic Transmission Fluids: Part 2: Origins of Friction-Sliding Speed Behaviour, M. Ingram1 , J. Noles2 , R. Watts2 , S.Harris,3 . H. A. Spikes1 1 Tribology Group, Department of Mechanical Engineering, Imperial College London, UK, SW7 2AZ 2 Infineum USA LP, Linden, New Jersey, USA 3 Infineum UK Ltd, Milton Hill, Abingdon, UK

Also see https://bobistheoilguy.com/automatic-transmissions-study/ Pages 18-22.

and afterwards we'll have a question and answer session.

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#### MolaKule

Staff member
is there any way we can determine the required coefficient of friction required in a transmission?
Yes, with expensive dyno studies.

Is there a way to see what kind of coefficient of friction an ATF provides?
This is a general misunderstanding of the coefficient of friction in general. The fluid, and its chemical properties, react with the surfaces in contact to give rise to friction coefficients or COF's.

Do we have any info on the coefficient of friction values?
Not publicly.
What makes different transmissions require different frictional values in a fluid? Or are they all the same?

This is my latest enigma.
Different engagement pressures, valve timing, wet clutch composition, fluid chemistry, and torque throughput determine the COF's.

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#### BMW Dom

CVT or Step-Shift?

Google these: LICENTIATE TH E S I S, Department of Engineering Sciences and Mathematics Division of Machine Elements, Wear Behavior of Wet Clutches by Niklas Lingesten

and

Frictional Properties of Automatic Transmission Fluids: Part 2: Origins of Friction-Sliding Speed Behaviour, M. Ingram1 , J. Noles2 , R. Watts2 , S.Harris,3 . H. A. Spikes1 1 Tribology Group, Department of Mechanical Engineering, Imperial College London, UK, SW7 2AZ 2 Infineum USA LP, Linden, New Jersey, USA 3 Infineum UK Ltd, Milton Hill, Abingdon, UK

Also see https://bobistheoilguy.com/automatic-transmissions-study/ Page 22.

and afterwards we'll have a question and answer session.
I was talking more about step-shift.

I'll read through the articles that you mentioned.

Are most transmission fluids, just a Dex 3 or Dex 6 based formula? Like Toyota ZF, etc...
That seems the only way for multi-vehicle ATFs to work? Or is it more of a compromise on clutch wear?
Who do we trust? The transmission manufacturer that says to only use a certain fluid ( usually proprietary unless Ford or GM, which they license their ATFs)
Or do we trust the fluid manufacturer that says that it will work?

#### CKN

I was talking more about step-shift.

I'll read through the articles that you mentioned.

Are most transmission fluids, just a Dex 3 or Dex 6 based formula? Like Toyota ZF, etc...
That seems the only way for multi-vehicle ATFs to work? Or is it more of a compromise on clutch wear?
Who do we trust? The transmission manufacturer that says to only use a certain fluid ( usually proprietary unless Ford or GM, which they license their ATFs)
Or do we trust the fluid manufacturer that says that it will work?
If it doesn't work you drain it out. I put Maxlife in my wife's Santa Fe that spec'ed for the Hyundai (very expensive) fluid. Valvoline says it's compatible (the manufacturer says Hyundai fluid only). Others have used Vavloine in their Hyundais . It hasn't blown up yet and operation is satisfactory.

I was talking more about step-shift.

I'll read through the articles that you mentioned.

Are most transmission fluids, just a Dex 3 or Dex 6 based formula? Like Toyota ZF, etc...
That seems the only way for multi-vehicle ATFs to work? Or is it more of a compromise on clutch wear?
Who do we trust? The transmission manufacturer that says to only use a certain fluid ( usually proprietary unless Ford or GM, which they license their ATFs)
Or do we trust the fluid manufacturer that says that it will work?
Most of them really need a certain viscosity range to correctly work, and it's not like there can't be room for error, which there is. most transmission fluids are probably generic dex 3 to 6 formulas. Keeps costs down.

#### MolaKule

Staff member
I was talking more about step-shift.

I'll read through the articles that you mentioned.
Are most transmission fluids, just a Dex 3 or Dex 6 based formula? Like Toyota ZF, etc...
That seems the only way for multi-vehicle ATFs to work? Or is it more of a compromise on clutch wear?

The secret is in the friction modification chemistry which is "adaptive" to a certain extent.

If you have some substantive data that shows Multi-Vehicle ATF's produce more wear than factory OEM fluids please present it.
Who do we trust? The transmission manufacturer that says to only use a certain fluid ( usually proprietary unless Ford or GM, which they license their ATFs)
Or do we trust the fluid manufacturer that says that it will work?

The DI additive package and ATF formulation was developed by the additive manf. who has tested it in a wide range of instrumented hardware, i.e. different transmissions, and who has determined their fluids will cover a number of transmission types and OEM hardware.

Whom you trust is a personal decision but I have seen the instrumented hardware and have used the DI packages and I trust them for their recommended coverages.

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#### BMW Dom

The secret is in the friction modification chemistry which is "adaptive" to a certain extent.

The DI additive package and ATF formulation was developed by the additive manf. who has tested it in a wide range of instrumented hardware, i.e. different transmissions, and who has determined their fluids will cover a number of transmission types and OEM hardware.

Whom you trust is a personal decision but I have seen the instrumented hardware and have used the DI packages and I trust them for their recommended coverages.
So it depends on the clutch disc? The article went way over my head?
Why aren’t there licenses like API for transmission fluid?
Having a study like Amsoil did for their atf would be interesting with different fluids and different transmissions.
I wish to understand, but it’s hard to

#### MolaKule

Staff member
So it depends on the clutch disc? The article went way over my head?
No, that is not what I said. I stated the Coefficient of Friction is a function of both the ATF's chemistry AND the composition of the wet clutch's surface and its composition.
Having a study like Amsoil did for their atf would be interesting with different fluids and different transmissions.
Those studies are very expensive as is the development testing by the DI manufacturers.

You do realize that the Amsoil study is part technical and part marketing. If you have the funding to do a comprehensive set of tests then let's talk about how it would be done.

Please Notice: The Amsoil study did not disclose any Mu(V) data so if an Amsoil-like study were to be performed on all of the fluids in the marketplace, what would Mr. Daily Driver learn from it?

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#### BMW Dom

No, that is not what I said. I stated the Coefficient of Friction is a function of both the ATF's chemistry AND the composition of the wet clutch's surface and its composition.

Those studies are very expensive as is the development testing by the DI manufacturers.

You do realize that the Amsoil study is part technical and part marketing. If you have the funding to do a comprehensive set of tests then let's talk about how it would be done.

Please Notice: The Amsoil study did not disclose any Mu(V) data so if an Amsoil-like study were to be performed on all of the fluids in the marketplace, what would Mr. Daily Driver learn from it?
I wasn't specifically mentioning the Mu(v) in the Amsoil study. I thought if the Mu(v) wasn't correct, it would wear the transmission out quicker.
My concern is the coefficient of friction and longevity of the clutch packs.

#### 4329

CVT or Step-Shift?

Google these: LICENTIATE THESIS, Department of Engineering Sciences and Mathematics Division of Machine Elements, Wear Behavior of Wet Clutches, by Niklas Lingesten

and

Frictional Properties of Automatic Transmission Fluids: Part 2: Origins of Friction-Sliding Speed Behaviour, M. Ingram1 , J. Noles2 , R. Watts2 , S.Harris,3 . H. A. Spikes1 1 Tribology Group, Department of Mechanical Engineering, Imperial College London, UK, SW7 2AZ 2 Infineum USA LP, Linden, New Jersey, USA 3 Infineum UK Ltd, Milton Hill, Abingdon, UK

Also see https://bobistheoilguy.com/automatic-transmissions-study/ Pages 18-22.

and afterwards we'll have a question and answer session.

The information on clutch plate materials state that the clutch plates are porous and have ATF additives adsorption.

If this is the case perhaps when a drain and fill is performed on the OEM ATF and is replaced by a multi vehicle ATF, is it possible that the OEM additive package remains in the clutch plates and therefore continues to provide acceptable performance levels.

This is simply my view so please correct me if I am incorrect.

#### MolaKule

Staff member
I wasn't specifically mentioning the Mu(v) in the Amsoil study. I thought if the Mu(v) wasn't correct, it would wear the transmission out quicker.
My concern is the coefficient of friction and longevity of the clutch packs.
Heat transfer from the clutch packs determines to a large extent the longevity of the clutch packs.

The frictional characteristics for most wet clutches are pretty well established.

#### MolaKule

Staff member

The information on clutch plate materials state that the clutch plates are porous and have ATF additives adsorption.

If this is the case perhaps when a drain and fill is performed on the OEM ATF and is replaced by a multi vehicle ATF, is it possible that the OEM additive package remains in the clutch plates and therefore continues to provide acceptable performance levels.

This is simply my view so please correct me if I am incorrect.
Yes, but let's say a complete replacement of all of the ATF fluid is done. The new fluid's additive chemistry will then displace the previous chemistry in the porous material. The Multi-vehicle fluid such as Valvoline's MaxLife ATF apparently has been shown to provide the same performance characteristics as many of the OEM fluids.

#### BMW Dom

Thanks, Mola!

This is a confusing topic for me, so your expertise provides immense help.
This is a lot more helpful then saying scare tactics like "only use OEM transmission fluid".

I remember reading that Dexron III and ATF4 have different coefficient of friction values.
What's your opinion on ATFs that are said to cover both? Like Amsoil's Signature Series Multi-Vehicle Synthetic Automatic Transmission Fluid?
I'm not trying to turn this into a crap on Amsoil thread.

#### nascarnation

One thing that's changed dramatically in the last 2 decades is the ability to use electronics to modify the pressure profile aka "adaptive" control. The controller is looking at rotational speeds and shift time and understanding how long each shift is, then changing pressures over time to conform to an "optimum" profile. At Allison we were able to accomodate 15W40 diesel engine oil, Dexron III, and 0W20 "arctic" MIL-spec synthetic oils without friction material or calibration changes.

#### PandaBear

is there any way we can determine the required coefficient of friction required in a transmission?
Is there a way to see what kind of coefficient of friction an ATF provides?
Do we have any info on the coefficient of friction values?
What makes different transmissions require different frictional values in a fluid? Or are they all the same?

This is my latest enigma.
I think that's what a clutch pack or transmission dyno is for. Some research labs use it.

#### Fauxchemist2009

Thanks, Mola!

This is a confusing topic for me, so your expertise provides immense help.
This is a lot more helpful then saying scare tactics like "only use OEM transmission fluid".

I remember reading that Dexron III and ATF4 have different coefficient of friction values.
What's your opinion on ATFs that are said to cover both? Like Amsoil's Signature Series Multi-Vehicle Synthetic Automatic Transmission Fluid?
I'm not trying to turn this into a crap on Amsoil thread.
Just don't use type 4 where WS is specified 😈