ATF and Friction Modification

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MolaKule

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In an engine, we want to reduce kinetic friction, but in an Automatic Transmission, we want a specific type of static/kinetic friction.

http://en.wikipedia.org/wiki/Coefficient_of_friction

discusses static and kinetic friction. The frictional characteristics we are discussing here is dynamic friction, a special kind of 'static/kinetic' friction. Dynamic friction is a friction that changes its "coefficient of friction" as two surfaces come in contact and are in relative motion, such as in AT clutch plates.

Recall that clutch plates have alternating layers of clutch friction material and steel plates. The friction material is splined on the inside, where it locks to one of the gears. The steel plate is splined on the outside, where it locks to the clutch housing.

The pressure for the clutches is fed through passageways in the shafts. The hydraulic system controls which clutches are energized at any given moment.

In AT's we want the fluid to create a specific dynamic friction coefficient (dependent upon the clutch materials used) such that we have smooth engagement and disengagement, so we don't have shudder or slippage. Shudder and slippage cause increased frictional material wear and increased heat.

It is this complex package of frictional modifier chemical compounds found in ATF that is important for smooth operation.

Remember, a friction modifier can be a friction reducer, a friction increaser, or one that controls friction in a specified manner.

In an engine, we primarily want friction reduction. In an AT, we want controlled friction modification often called Mu(V) in the literature. The fluid must provide a specific friction versus velocity relationship.

There is a phenomenon commonly called "stick-slip" or "dynamic frictional vibration" and manifests itself as "shudder" or low speed vibration in the vehicle. Using friction modifiers in the ATF prevents this shudder.
 
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ATF's are not the best lubes for synchronized mtl's., they are a compromise.

Needle bearings and improved ball and roller bearings and hardened races can still operate in this lower viscosity environment of ATF.

I think there are exceptions in which certain transmissions can show low wear initially, but I still fear long-term wear problems with ATF's, since the anti-wear package in ATF really isn't suited for long-term wear protrection. And the lack of friction modification normally used for smooth synchro operation is not present in ATF's.

Personally, if I had to use ATF's in a tranny, I would use the highest viscosity ATF I could get my hands on, such as one that had say close to 8.0 cSt @ 100C and up to 10 cSt, such as Amsoil ATD and the Redline Hight-Temp and Synthetic Racing oils.

And then I would change to the GM Synchromesh mtl oil of 9.3 cSt.
 
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I am using Amsoil ATF in my jeep 242 transfer case, Should I consider MTF next change? Thanks
 
I put a left over 1/2 quart of Amsoil MTF in my Jeep's TC along with 1 quart of Amsoil ATF. The car is still working fine, though it has only seen on road use. If the car were to see heavy off road use, I would put in all MTF.

I wonder if a good PCMO would be better than ATF due to the increased AW?
 
The problem I have with PCMO's is that the there is no mtl specific friction modifier in it.
 
I have an application (NVG T-850) that spec's ATF+4 & 4oz of Mopar LSD Friction Modifier. It also has a Quaife ATB Differential which is gear operated, no plates or clutches. Now Quaife has stated that it's ATB Diff does not require any FM's, so why does Dodge want it in there? I suspect it's to "bump up the viscosity" of the ATF? Also there is an addendum to the owners manual that requires a fluid change interval of every 18k miles instead of every 48k miles. That makes me think the FM is breaking down the ATF?

So my question is what fluid would be "best" for this trans? Right now I am running RP Syncromax and it seems to be much smoother.
 
Is this gearbox a manual transaxle or automatic transaxle and in what vehicle?

Giving numbers doesn't necessarily imply we know what they mean.
 
So it's a transaxle arrangement where the mt and diffy are in the same case?

Logically, it doesn't make sense to ad an LSD FM to a manual tranny with a torsen type diffy.
 
So I shouldn't have any trouble, in fact I may benefit from running a synchromesh type MTF like Amsoil's Synchromesh MTF or a GM type synchromesh fluid over the ATF that is spec'd?
 
Correct. If you do use it, let us know how it shifts.

I would try the GM Synchromesh fluid or the Pennzoil equivalent first, then the MTF or Redline MTL.
 
I just changed over to RP Syncromax about 5k miles ago, but I do have 3qts of the Pennzoil Synchromesh fluid on hand and I may just swap out the RP at the next oil change. I notice you have recommended the GM/Pennzoil synchromesh fluid in other posts, any particular reason you seem to like it over say the Amsoil offering?
 
NO, the answer was viscosity driven.

The GM Synchromesh mtl is about 2.3 cSt viscosity units above say a DexronIII/Mercon fluid, whereas the Amsoil MTL is about 3.5 cSt above the ATF. One wants a fluid viscosity as close to the original as possible, but with better AW protection.
 
Thanks for the reply, just a couple more things. 1. Is there any chance that Specialty Formulations will start blending anytime soon? 2. Do you have an opinion on BG Synchroshift MTL?
Thank's for all the info..
 
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