Effect of ATF Friction Modifiers in a Power Steering System?


$50 Site Donor 2023
May 22, 2012
My Volvo 240s have a GM Saginaw Type II pump and a TRW/CAM rack. The fluid spec varies, Type F in some manuals, ATF (no spec) in others. I’ve been filling with DEX VI, Mercon V full syn, or M1 ATF with no issues. And no pump squealing during below 0 degree start ups.

When the folks on the Volvo 240 sites learned of this some were sure the seals would be destroyed by FMs and that only Type F will work. Others completely disagreed.

What is the effect of FMs in a PS system? Should I be concerned? Thanks in advance for your help.

Please have those people identify the chemistry that affects seals and HOW that chemistry affects the seals.

Friction Modifiers have little effect on seals and are not an issue so this is another case of the spouting of disinformation before they have educated themselves.

Mola said:
ATF if a special hydraulic oil for the following purposes:
Lubrication for gears.
Cooling and heat transfer.
Transmitting torque via the Torque Converter.
Friction modification for clutch packs, bands, Torque Converter Clutch.

One of its more important duties of ATF is to make sure the fluid's coefficient of friction is matched to the friction materials inside the tranny. I.e., to ensure the proper static and dynamic coefficients of friction during engagement/disengagement.

In the early days of AT's the clutch material was composed of cellulose material with cotton and other soft materials in a phenolic resin binder. Today, hybrid materials are used.

Hybrid (or composite) materials are typically manufactured using a process similar to that used for paper-based materials, but using carbon fibers in combination with organic or synthetic fibers such as Kevlar and Aramid fibers. So Friction Materials may include cellulose, carbon fiber, Aramids, fiberglass, or a combination of materials (composites). Today, composites are the norm.

Many of the clutch materials from various manufacturers are close in terms of static and dynamic friction coefficients.

The clutch disc material of Automatic Transmissions, and other wet clutch applications, are made of porous friction materials which are bonded to steel core plates.

Note: Sintered metal composites may be found in HDD applications.

This material must exhibit:

1.) Mu(o), low speed dynamic coefficient; affected by friction material ingredients and ATF additives adsorption

2.) Mu(i), initial dynamic coefficient at high speed; affected by hydrodynamic effects/porosity/compression/roughness.

When an additive company tests its ATF additive package, many transmissions are run through the SAE2 and other friction test machines (JASO M349-98, R-H Friction Apparatus, ZF GK Test Bench, Low Velocity Friction Apparatus, etc) to determine if the Friction Modifier set is appropriate.

The friction characteristics (Mu verses Velocity) of the clutch/fluid system are carefully monitored for each separate transmission and fluid formulation.

Mu is coefficient of friction plotted on the vertical axis, V is the relative speed of rotating components plotted on the horizontal axis. Mu(v) then is the resulting curve of the frictional characteristics of the clutch/fluid system.

The appropriate FM additive type and levels are then determined for the complete additive package.

A sample of the ATF Friction Modifiers are shown below:

fatty phosphites, fatty acid amides, fatty epoxides, borated fatty epoxides, fatty amines, glycerol esters, borated glycerol esters, alkoxylated fatty amines, and borated alkoxylated fatty amines, metal salts of fatty acids, sulfurized olefins, fatty imidazolines, non-hydroxyl fatty tertiary amines, and any mixtures of the above.

The exact composition of and specific chemistry (molecular structure) of the Friction Modifier(s) are closely guarded secrets.

With the many different chemistries and potential mixes available, I think one can now see why Mutli-Vehicle fluids can be manufactured.

Ford Type "F" ATF is a fluid with very low levels of friction modification and has a Mu(V) curve separate and apart from either the Dexron Series or the Chrysler ATF+ series.

Ford Type "F" ATF is often used today in racing transmissions such as the PowerGlide and TH400 Turbohydramatics because of the positive lockup, IE, little to no slip in the clutch packs during engagement.

Chrysler ATF+ fluids are on the other end of the spectrum and exhibit a completely different Mu(V) characteristic. The ATF+ fluids are highly friction modified.

For a more Technical Study on ATs and heat transfer one can go to:


Smooth engagement and the elimination of shudder are the primary reasons for the development of ATF friction modifiers.

Friction coefficients are the result of the fluid/material interaction at the mating surfaces.

Friction modification in transmission fluids does not mean the reduction of friction, but rather the matching of friction coefficients at different rotational speeds.

Friction modification can mean Increasing Friction, Reducing Friction, or the Modification of friction for matching friction requirements in rotating components.

ATF friction modifiers are different than engine oil friction modifier, are different than LSD differential lube friction modifiers, and are different than those used in Manual transmissions.

In other words, you have different and specific friction modifier chemistry for each type of lubricant.
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Please have those people identify the chemistry that affects seals and how this chemistry affects the seals.

Friction Modifiers have little effect on seals and are not an issue so this is another case of the spouting of disinformation before they have educated themselves.

Thanks Mola!
Don't most systems these days call for ATF? I know my Tacoma does. Been running Maxlife life in it for a couple of years now. No issues to date