Hydraulic Clutch altered functionality with heat, or something else???

I've got one that has me scratching my head.

I installed one of Forte's ( i reference it coming from Mike only so that people may have a better idea of what it is, not to blame the quality or Mike for any of this situation) Hydraulic clutch kits in my MK4 (with Coyote). It worked great for a few months (maybe 1500 miles) and then I started to notice that as I drove the car, the throw of the clutch would degrade, as in it would be difficult to shift gears to the point that it would grind rather badly, or be very difficult to even get into first gear at a stoplight. When this would happen I would lift the car, and readjust the rod from the slave cylinder to make the throw longer, thereby engaging the clutch more fully, and the problem would go away. Within a few days, or weeks, the problem would return. I made an assumption initially that the nut holding the slave cylinder rod was vibrating loose and the length was reducing as I drove, so finally put some locktite on the nut and that seemed to work for awhile. I thought it was fixed. (I also should mention that I fully bled the clutch a couple of times because I was concerned that there was air in the line which was causing the issue when the fluid heated up after driving) so am fairly confident that there is no air in the line.

Now, the problem is back again. I'd used blue loctite, which I'm thinking may have just loosened under heat, so am considering doing the whole thing again with red loctite, or even welding the nut to hold the position.

I'm sure that all sounds logical. BUT HERE IS WHERE IT GETS WEIRD.

When the clutch starts acting up, if I sit the car for a few hours (overnight) and then drive it in the morning, it generally works just fine, until the heat builds up again. So, I must assume that it is not the length of the slave cylinder rod at all, because it wouldn't "reset" the position of the nut and thereby the length without me doing anything.

So, the two things I'd thought might be causing the issue 1) air in hydraulic fluid and 2) rod in slave cylinder vibrating and thereby changing the throw length don't really fit the symptoms completely. I still plan to loctite (red) the rod just to be safe, but I'd sure appreciate if anyone else has any thoughts of what could be happening. I'm just struggling to figure out what it could be. (BTW, I've got just over 2500 miles on the car, and all parts, including the clutch and transmission TKO600 were brand new)

Is it possible that you don't have enough free play in the clutch pedal so that the fluid cannot refill the master cylinder? As things warm up you might need a bit more travel, but there's not enough fluid in the system. The fluid flows back and forth from the master to the reservoir through a small hole. IF the pedal does not retract all the way, the hole may be blocked.
Mike

Well, that sort of makes sense to me. Not to seem stupid here, but I'd assume I'd check that by letting the clutch out, and looking at the master cylinder just to see if it isn't opening all the way? if this is the case, any ideas on how I'd adjust for more free play?

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Originally Posted by michael everson

Is it possible that you don't have enough free play in the clutch pedal so that the fluid cannot refill the master cylinder? As things warm up you might need a bit more travel, but there's not enough fluid in the system. The fluid flows back and forth from the master to the reservoir through a small hole. IF the pedal does not retract all the way, the hole may be blocked.
Mike

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Do you have the Wilwood pedal box or the stock Mustang one? If Wilwood, I don't think there is a stop unless your clutch pedal is hitting something before it retracts all the way
Mike

Like Mike, I suspect this is not necessarily heat related...it symptoms just show up at the time the system is "hot."

One exception could be heat impacts on the line from the reservoir to the hydraulic MC. If the reservoir or the line soak in a lot of header heat the hydraulic oil viscosity will go up. Some in my local club actually experienced loss of braking power because the hydraulic oil (brake fluid) over heated between reservoir and the MC.

If you are locking up more fluid between the MC and the slave cylinder, the level in you reservoir will go down and the slave cylinder will not retract as much. You could do a before and after check on the reservoir level and the rod position on the slave cylinder. I think this would confirm that the fluid is not returning properly.

I am also assuming your using the correct sized MC ... I have read on the forums this can impact performance significantly. According to the Forte installation instructions the free play is important as well.

The fix would depend on the pedal box used. I have the Wilwood which allows adjustment between the top of the pedal and the MC.

Carl

How much heat is it exposed to? What fluid are you using? I'd think that either the cylinder or line would have to be awfully close to the heat source for it to occur but what you're describing (i.e. clutch activation going away when hot and returning when cooled) makes it sound like you are boiling the fluid.

Jeff

Whichever pedal box and MC you have the goal is the same. When the clutch pedal is fully up, you should be able to feel a tiny amount of freeplay in the pushrod. Is there a plunger type switch which contacts the pedal arm when it is fully up but it needs adjustment to allow more up travel? Another thought is the bleed process. When I was helping Bil3422 w/ his internal hydraulic clutch we spent 2 hours trying to get the thing bled. He finally called the people he bought the slave system from. They explained it this way. Hydraulic brakes are a high pressure low volume system so they respond to the usual push the pedal procedure. Hydraulic clutches are a low pressure high volume system so they need a different procedure. After his recommendation of pressure bleeding we cobbled up something w/ a small air pump (fish tank?) and a bunch of hoses to step up to the diameter of the reservoir and in about two minutes we had a clutch.

Wilwood....

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Originally Posted by michael everson

Do you have the Wilwood pedal box or the stock Mustang one? If Wilwood, I don't think there is a stop unless your clutch pedal is hitting something before it retracts all the way
Mike

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Using DOT 4 for fluid, so I wouldn't expect it to boil too easily. One of the first things I did was to wrap the hydraulic line with a heat insulation tape. It didn't seem to make any difference.

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Originally Posted by Jeff Kleiner

How much heat is it exposed to? What fluid are you using? I'd think that either the cylinder or line would have to be awfully close to the heat source for it to occur but what you're describing (i.e. clutch activation going away when hot and returning when cooled) makes it sound like you are boiling the fluid.

Jeff

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