What does it mean when a fluid is highly friction modified?
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A highly-friction-modified ATF reduces friction in the band and brake friction facings to smooth the shifts. It has no effect on metal wear characteristics over past non-friction modified ATFs. An example of a non-existant friction modified ATF would be the old Ford "Type F" specification. Examples of ATFs that are probably at the pinnacle of highly-friction-modification characteristics would be DaimlerChrysler's "ATF +4" or Ford "Mercon V". Most manufacturers are steering toward fluids with higher friction modification characteristics with the exception of G.M. so far. "Dexron" through "Dexron III" are also friction modified, but no where to the degree of other car manufacturers' current proprietary ATFs.
Seamless shifting seems to be a GM tranny trademark, even with dextron III. It really annoys me though. I am too used to performance trannys.
[ August 30, 2003, 11:15 PM: Message edited by: sbc350gearhead ]
[ August 30, 2003, 11:15 PM: Message edited by: sbc350gearhead ]
The way friction modifiers in ATF were explained to me is this: With a normal trans fluid (Ford type F ATF) static friction is greater than kinetic friction - meaning it's harder to make something slip than to keep it slipping. A friction modified trans fluid works the opposite way - it's easy to slip the band or clutch a little bit, but then it locks up. This property contributes to smooth shifts but keeps the trans from slipping constantly.
Agree. G.M.'s choice of clutch and brake friction material comes into play in the delicate balance with their Dexron III fluid's friction modifier content (Is this the same as the mythical "Dextron" ATF that keeps popping up in different threads? Perhaps they only use trannies requiring Dextron fluids in vehicles powered by Cummings engines...
[ September 01, 2003, 11:45 PM: Message edited by: Ray H ]
Sorry, the only Hyundai I have driven is a friend's 99 elantra. When that thing shifts, it feels like the tranny is about to fall out. I think that there was a problem with that tranny, as the first one went out at 30k miles and the new one only has 30k miles and it already shifts like crap. The car is very poorly maintained though. I haven't had a chance to drive a new model. I may have to check one out.
MolaKule
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Well, three-speed with overdrive. If you're pulling anything, it's a three-speed.
MolaKule
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Nissan's new three-speed automatics on their Pathfinders shifts like butter and cream, and are using Dexron III as well.
The base oil provides a certain amount of friction modification, but for the correct 'stick-slip" characteristics, additional frictional additives must be added. Most friction modifiers today are of the ashless types and are high viscosity natural and synthetic esters.
The Viscosity Index Improvers (VII's) also modify the friction coefficients as well, and are ashless synthetic fluids of the polymer variety.
[ September 03, 2003, 12:45 PM: Message edited by: MolaKule ]
The base oil provides a certain amount of friction modification, but for the correct 'stick-slip" characteristics, additional frictional additives must be added. Most friction modifiers today are of the ashless types and are high viscosity natural and synthetic esters.
The Viscosity Index Improvers (VII's) also modify the friction coefficients as well, and are ashless synthetic fluids of the polymer variety.
[ September 03, 2003, 12:45 PM: Message edited by: MolaKule ]
3spd Auto? I didn't think ANYONE made those anymore.
FWIW I just got through reading where the author suggested using Type F in older TH350 or TH400 to obtain 'sharper' shifting action.
This discussion also makes me think Type-F (or Dexron) to be better suited than some of the others for power steering applications. Now that I think about it, I seem to see those 2 more commonly recommended by manufacturers for PS pumps - maybe the friction modifiers (or lack thereof) is the reason?
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