Possible slave cure ??? - Ranger-Forums - The Ultimate Ford Ranger Resource


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Old 09-24-2009
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Possible slave cure ???

After responding to this thread

https://www.ranger-forums.com/forum2...hing-dumb.html

It got me to thinking that maybe this has something to do with the short lifespan of many of our slave cylinders.
If the master cylinder reservoir is filled , and the rubber cup inside it is also filled by mistake , Add in the heat generated from the engine/weather ,The fluid will expand.
Since the rubber cup is also full , thereby eliminating any air needed for expansion , the fluid has to expand somewhere.
Toward the slave cylinder.
Not knowing the actual clearance between the throwout bearing face and the fingers on the pressure plate , lets assume it's .002 inch.(the bearing face should not be contacting the pressure plate when the clutch is not depressed.)
If the fluid heats , say 20 degrees, and expands, it may be enough to let the throwout bearing lightly ride on the pressure plate fingers.
With the bearing spinning constantly , it may generate heat to further warm the fluid in the slave making it expand farther.
Over time the bearing seal wears out due to the constant spinning.
In summary, when checking the fluid level in the clutch master cylinder,be sure to remove the rubber cup and make sure it is empty before replacing it.
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Old 09-24-2009
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Quote:
Originally Posted by OTRtech View Post
After responding to this thread

https://www.ranger-forums.com/forum2...hing-dumb.html

It got me to thinking that maybe this has something to do with the short lifespan of many of our slave cylinders.
If the master cylinder reservoir is filled , and the rubber cup inside it is also filled by mistake , Add in the heat generated from the engine/weather ,The fluid will expand.
Since the rubber cup is also full , thereby eliminating any air needed for expansion , the fluid has to expand somewhere.
Toward the slave cylinder.
Not knowing the actual clearance between the throwout bearing face and the fingers on the pressure plate , lets assume it's .002 inch.(the bearing face should not be contacting the pressure plate when the clutch is not depressed.)
If the fluid heats , say 20 degrees, and expands, it may be enough to let the throwout bearing lightly ride on the pressure plate fingers.
With the bearing spinning constantly , it may generate heat to further warm the fluid in the slave making it expand farther.
Over time the bearing seal wears out due to the constant spinning.
In summary, when checking the fluid level in the clutch master cylinder,be sure to remove the rubber cup and make sure it is empty before replacing it.
The hydro clutch uses brake fluid correct? Brake fluids (quality fluid) shouldnt expand enough to cause a problem like this. I could see if you didnt bleed the system well enough that air in the system could expand. But I dont think the properties of brake fluid will do this.
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Old 09-24-2009
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Different brake fluids expand at different rates at a different temperature. That's why you use dot4 in sportbikes, the heat generated is enough to boil dot3.

Of course, having a more heat resistant fluid would not make it any less susceptible to clearance issues as it would still expand and if it was overfull, contact the pressure plate...

Its an interesting theory I would like to see what the ex ford engineer that drags his ranger thinks. Can't remember his name though.
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Old 09-24-2009
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The clutch master has a vent hole in the cap, maybe 0.060". Wouldn't that take care of any possible expansion problem above the diaphragm, whether it be fluid or gas?
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Old 09-24-2009
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Mine has no such vent that I could find.
But even without it , the air inside the cup/diaphram would compress unless it was full of fluid.
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Old 09-24-2009
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Originally Posted by OTRtech View Post
Mine has no such vent that I could find..
Mine has the vent, I just went and looked. It's a small hole right through the top of the cap, maybe 1/16".

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Originally Posted by OTRtech View Post
.....unless it was full of fluid.
I thought that was the theory - the volume above the diaphragm might be incorrectly filled with fluid and have nowhere to go except to the slave. A vented cap should take care of that.
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Old 09-24-2009
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So according to the link in the OP ,Fluid should not have come out under pressure , Unless,there may be either caps with no vents or caps with faulty vents ?
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Old 09-24-2009
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Originally Posted by OTRtech View Post
So according to the link in the OP ,Fluid should not have come out under pressure , Unless,there may be either caps with no vents or caps with faulty vents ?
I haven't looked at a 2009 so I don't know if it is vented or not. I can say this much though: my cap is vented and my slave failed unexpectedly at 19,000 miles from new. So, at least in my case, the cause was not from a pressure buildup in the clutch master reservoir.

Honestly, I think the stock plastic slave is just not up to the job. Simple as that. There are quality hipo/racing concentric slaves available but I have never seen one for a Ford truck application. My feeling is that the aftermarket is missing out bigtime on this one. I would be willing to pay $200 or more for a quality replacement that I could trust to get me home. As far as I know, that option doesn't exist.
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Old 09-24-2009
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So if my OP is not the cause , Is it possible to measure the distance from the pressure plate fingers to the front of the slave to see if there is any clearance at all ?
If the bearing is constantly riding against the fingers it's got to wear something.
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Old 09-24-2009
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Mine has gone out 3 times in 4 years. I used to drive my truck really hard and offroad but now it just stays on the road and it still fails. Its just cheap parts.
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Old 09-24-2009
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Originally Posted by OTRtech View Post
So if my OP is not the cause , Is it possible to measure the distance from the pressure plate fingers to the front of the slave to see if there is any clearance at all ?
If the bearing is constantly riding against the fingers it's got to wear something.
I don't know if you could do that through any of the openings with the rubber plugs on the driver side of the bell housing. Maybe.

Personally, I have totally given up on Ford's internal slave. It is the entire reason that my truck got an automatic when I did the V8 swap. Actually, right now today, I'm in the middle of modding a M5ODR2 (F-series) transmisson to accept an external slave. I want a stick again but it has to be more reliable than before. Or, if not totally reliable, at least easily repairable if the slave does fail.
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Old 09-24-2009
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It will wear the bearing. There is no seal being rotated on these slaves. The bearing itself is a separate piece, and can be changed independent of the slave, though the slave usually goes out before the bearing. You theory, while showing critical thinking and creativity, has a few flaws. The vented cap, which will vent fluid as well as air. The expansion rate of brake fluid, even dot 3 fluid has very little expansion over a 50 degree range, much less 20. And the bearing contacting the pressure plate will wear the bearing, not the slave itself.
I'm with Bob, I think it's the cheap plastic construction, that over time deforms, losing is sealing surface integrity, and thereby losing pushing force.
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Old 09-24-2009
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Whatever it is it should have been fixed by ford already. I only have ~60000km on mine and its already noticeably hard to get it in gear sometimes... And I rarely use it for anything but starting from a stop.

It frustrates me to no end that at any moment I could lose my clutch totally.
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Old 09-24-2009
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Whatever it is it should have been fixed by ford already
Key words there are SHOULD HAVE but they haven't done a damn thing about it.Yeah its only a $40 or $60 part but you have to pull the tranny to do it and some of us don't have the time, space or tools to do it so I have to pay someone to do it every time.
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Old 09-25-2009
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^^Maybe that's the reason why they've not fixed it.
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Old 09-28-2009
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good point if the dealership is makin money why fix it? lol thats how they run.
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