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#498495 - 12/26/02 10:12 PM What do Friction Modifiers Do?
Giles Offline


Registered: 12/02/02
Posts: 403
Loc: California
I've been wondering what friction modifiers to for transmissions and rear ends. What happens if you add more friction modifier than is required?

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#498496 - 12/27/02 03:02 AM Re: What do Friction Modifiers Do?
metroplex Offline


Registered: 09/12/02
Posts: 1904
Loc: SE MI
Nothing,.

Some gear lubes are formulated for use with limited slip differentials, and that's what friction modifier is used for - quieting down the clutches in some limited slip applications.

If you have an open diff, don't worry about it.

I bought some Redline gear oil which is formulated for use w/ LSDs

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#498497 - 12/27/02 04:45 AM Re: What do Friction Modifiers Do?
dkcase Offline


Registered: 10/20/02
Posts: 728
Loc: Suburban St. Louis
quote:
What happens if you add more friction modifier than is required
quote:
Nothing,.
But mustn't there be a point where too much friction modifier will cause the clutches to slip and wear and not engage properly... ?

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#498498 - 12/27/02 07:52 AM Re: What do Friction Modifiers Do?
Bror Jace Offline


Registered: 05/27/02
Posts: 4854
Loc: Saratoga, NY
As far as I know, friction modifiers can either increase or decrease the coefficient of friction a fluid has.

In the case of limited slip or synchromesh applications, the FMs should INCREASE the coefficient of friction.

--- Bror Jace

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#498499 - 12/27/02 04:38 PM Re: What do Friction Modifiers Do?
metroplex Offline


Registered: 09/12/02
Posts: 1904
Loc: SE MI
dk: how much friction modifier are you adding???

Ford calls for 4 oz for their 7.5/8.8/9.75 rear ends.

I just buy the stuff thats formulated for use in LSDs and not worry about adding FM.

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#498500 - 12/28/02 08:51 AM Re: What do Friction Modifiers Do?
Giles Offline


Registered: 12/02/02
Posts: 403
Loc: California
Thanks for all the replies, I'm learning something. I have a specific question about tranny fluid. Mercon V is supposed to be heavily friction modified, would this be lowering or increasing the coefficient of friction? My understanding is it will get rid of shudders in the tranny or torque converter but I'm not sure how it's doing that. Do friction modifiers extend the life of the tranny or just make it smoother?

Just for a point of discussion, what would happen if you added double the amount of friction modifier to a Mercon fluid that converts it to a Mercon V fluid?

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#498501 - 12/27/02 09:56 PM Re: What do Friction Modifiers Do?
Bror Jace Offline


Registered: 05/27/02
Posts: 4854
Loc: Saratoga, NY
"Do friction modifiers extend the life of the tranny or just make it smoother?"

I've always thought of adding a friction modifier (increaser) as a last-ditch effort to keep a tranny going before rebuild. Usually, by this point, the bands are shot.

Some shudder prone trannies, however, like a little more friction in their fluid and respond well to the additive.

--- Bror Jace

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#498502 - 12/28/02 07:18 AM Re: What do Friction Modifiers Do?
Alex D Offline


Registered: 11/28/02
Posts: 666
Loc: Triad, NC
Actually friction modifiers do just what it says modify friction. Most make the fluid "slicker" than it originally is, such as the Limited slip additive from GM, but also LubeGard HFM, which is used to bring Dexron ATF to standards for Chrysler ATF 3+ and Honda ATF fluid (these are much slicker than Dexron and without lubegard you get clutch shudder and the trannies wear out much faster). I actually have never seen a friction modifier that makes any fluid "grabbier" than it was. All FMs I know make the fluid "slicker"

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#498503 - 01/06/03 06:08 AM Re: What do Friction Modifiers Do?
Pete2k_Z28 Offline


Registered: 01/01/03
Posts: 12
Loc: NJ
Perhaps I can lend some insight to the topic?

Before you can understand how friction modifiers function, it is important to understand how "wet" clutches perform.

In a wet clutch arrangement, there are three stages of engagement. During the first stage, the clutch is not in contact with the pressure plate or other metal plate. We will use an automatic transmission torque converter as an example. Anyone who has driven auto trans cars with lockup torque converters for a while has probably experienced a phenomenon known as "lockup shudder" or "torque converter shudder". Shudder is caused during torque converter clutch lockup by burnt fluid or fluid wich has exhausted all of it's friction modifers. The result is a chattering feeling when the torque converter goes into lockup mode. I will now attempt to explain the physics of wet clutch engagement.

As I have already mentioned, during the first stage the clutch is not in contact with it's mating surface. The fluid itself, however, is acting as a viscous coupling, causing a partial engagement. A side effect of this is heat, and I believe you all know that heat is the killer of automotive oils.

The second stage is very simlar to the first. At this point the clutch is very close, possible within thousandths of an inch, from it's mating surface. The viscous coupling is now more effective, but the pressure and shear load on the fluid are also higher, and the result is increased heat.

During the third stage, the clutch actually contacts it's mating surface and positive engagement is reached. The shear load of the fluid has been overcome and has either extruded itself outside of the clutch material or, depending on the application, has partly or entirely extruded itself through a porous friction material, thus exiting the engagement area of the clutch.

Now that we have an understanging of wet clutch engagement, lets see how that plays out in the real world. If a fluid has lost a substantial amount of the friction modifier, the shear of the fluid will be inconsistant accross the engagement surface and the clutch will briefly alternate between full engagement (stage 3) and viscous engagement (stage 2). The as power through the assembly varies, wich is connected in our case to a vehicle that we are inside of, a bucking of sorts is perceptable to it's occupants as power transmitted to the wheels is momentarely interrupted and regained.

In an application like a limited slip rear end, similar phenomena occur but in a slightly different manner. Because the clutch plates are constantly loaded with heavy springs, in theory they should always remain in stage 3 of lockup. If that were the case however, they would never slip. So the purpose of a friction modifier in a rear end is to ensure that the transition from S3 to S2 and back again during cornering etc. is smoothe. Therefor chatter occurs in much the same way it does in our torque converter clutch scenerio.

So the answer to your question if friction modifiers enhance friction or reduce it? The answer is there is no answer. Depending on what the application calls for and how it is engineered, they can do either. So as Alex said, it does just that; modifies friction.

And now hopefully you will understand why and how as well [Smile]

Pete

[ January 06, 2003, 10:09 PM: Message edited by: Pete2k_Z28 ]

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#498504 - 01/06/03 06:25 AM Re: What do Friction Modifiers Do?
TheLoneRanger Offline


Registered: 05/27/02
Posts: 1454
Loc: Southeast United States
Good explanation, Pete. [Cheers!]

I guess that's why they're called friction "modifiers", instead of "friction reducers" or "friction enhancers".

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#498505 - 01/06/03 07:03 PM Re: What do Friction Modifiers Do?
metroplex Offline


Registered: 09/12/02
Posts: 1904
Loc: SE MI
Actually the FM added to gear oil REDUCES friction to eliminate chatter.

The pros recommend only 1/2 of what the manuf recommends - i.e. 2 oz instead of 4 oz of Ford FM additive.

This gives you tighter locking action.

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#498506 - 01/06/03 07:12 PM Re: What do Friction Modifiers Do?
MolaKule Offline


Registered: 06/05/02
Posts: 14116
Loc: Midwest
Metroplex is correct. Friction Modification is the newer term for "friction reduction."

To increase the friction coefficient of a fluid, you simply REDUCE the amount of Friction Modifier that you add to the fluid. Likewise, to reduce the coefficient of friction of a fluid, you increase the amount of friction modifier in the fluid.

Chatter is caused by dynamic friction, which is also called "stick-slip."

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#498507 - 01/07/03 08:11 AM Re: What do Friction Modifiers Do?
TheLoneRanger Offline


Registered: 05/27/02
Posts: 1454
Loc: Southeast United States
What about "Ways oil" that is used in the machine tool industry? IIRC, the oil is modified to have more friction when in motion than at rest, so slides will not overrun their tracks.

Granted, in the automotive area the friction modifiers seem to be used to get a lower Fc.

[ January 07, 2003, 03:23 PM: Message edited by: TheLoneRanger ]

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#498508 - 01/06/03 11:06 PM Re: What do Friction Modifiers Do?
Giles Offline


Registered: 12/02/02
Posts: 403
Loc: California
Pete, thank you for an excellent explanaintion and all the other contributers as well.

I'm trying to determine if the behaviour of my transmission is normal but I've never had one that has "Shudder" that I know of. Can someone that has experienced shudder describe it in a way that I would recognize it? Pete's explaination is pretty good, but I'm not sure what frequency of the shudder is. Does it disengage temporarily and then reengage in a matter of once a second, or rapidly like 10 times a second? Does it make noise and can passengers feel it or only the driver?

I've had an occation where the transmission felt like it slipped, and then recovered quickly, but it doesn't feel like shudder to me. This usually happens when slowing down and then speeding back up. It feels more like it temporarily slips and then grabs for good while accelerating. Would adding more friction modifier make it less likely to slip?

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#498509 - 01/06/03 11:15 PM Re: What do Friction Modifiers Do?
MolaKule Offline


Registered: 06/05/02
Posts: 14116
Loc: Midwest
Shudder is like when you take your fist at your ear level and pretend to punch from just behind the ear to in front of your ear rapidly.

It is a forward and rearward oscillating sensation occuring from 5 to 10 times per/second.

Giles,

In your case, sounds like normal AT shifting.

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