Clutch Issue - I can't figure out what the issue is

[Slider]

My FF Roadster (Coyote, TKO600, Hydraulic Clutch from Forte) has been on the road for about 5200 miles over the last 4 years. It's been bullet proof and not given me a problem EXCEPT I've been having a weird issue with my clutch. The problem only seems to come on when I'm driving in stop and go traffic, or it's warm outside. As the car heats up, the clutch stops working, to the point where even with the clutch depressed all the way the car is still pulling. Essentially the clutch isn't engaging. If I shut the car off for awhile, the car cools, and the clutch works fine. Now, in my mind this tells me that the hydraulic fluid must have air in it and the bubbles are heating up and causing an issue. So, I rebled the clutch a couple of times but the problem did not resolve. I had someone much more experienced then I bleed the clutch to their point of satisfaction and the problem did not go away. (BTW, there is no leak in clutch fluid at any point in the system. No leaks and no drop in fluid levels over months).

My next step was to pull the slave cylinder and adjust the bar (Threaded rod) within the cylinder to better engage the clutch when depressed. This worked.... for awhile, and then after a couple of weeks the problem would come back. I figured that the nuts controlling the length of the bar (sorry I don't know the proper name of this bar) must have vibrated and somehow the bar shortened itself. So I put locktight on the nuts, and the issue still happened. So I welded the nuts and the issue still came back. Finally, I cut a longer bar (threaded rod) and welded the nuts so that there was more rod to engage the clutch, and it seemed to have solved the problem... for about 500 miles. Tonight (a nice cool fall night) I was out for a drive and the issue appeared again. Sitting at a light, in traffic, I had to shut off the car as it was pulling strongly enough that I was spinning the rear tires with the brakes depressed. Additionally, in first gear I could let off the gas completely and leave the clutch out and it would not stall out. At this point I couldn't easily shift out of gear, or back into gear (Again the clutch wasn't fully engaging). I pulled over and parked for about an hour. Started the car up and drove about 20 miles home and it worked as perfectly as can be. Shifted beautifully.

So my assumption is that my lengthening of the bar within the slave cylinder on the hydraulic clutch set up from Forte was a bandaid fix that engaged the clutch better... for awhile, and then when it heated up enough, the problem returns.

I would so appreciate any thoughts on where to start looking at what the problem might be. I've had people tell me that the master cylinder must be leaking air in, causing bubbles when the fluid heats and thus making the clutch not engage enough. I've had others tell me to put a longer "threaded bar" in the slave cylinder since it worked before, but again, adjusting that seems like a bandaid. I want it fixed properly because it's scary as hell to find that you can't take the car out of gear and it just wants to go...

Any thoughts, or anyone who has experienced something similar? I'm all ears at this point. Thanks in advance

[karlos]

With respect to the overall clutch pedal travel, does the point at which the clutch starts to engage move up (toward the top of the pedal travel) when the issue occurs? If so you probably have a pushrod adjustment issue. There should be a small amount of clearance between the pushrod and the piston in the slave cylinder to accommodate the increase in fluid volume that occurs when the fluid heats up. If no free play the fluid can't return to the reservoir and the pedal stroke then becomes insufficient to disengage the clutch. The fact that the issue comes and goes with heat is a pretty strong clue.

Here's a link to an article that describes what appears to be happening in more detail. It's not Cobra-specific but still provides some good insight. Hopefully just a quick adjustment is all you need to set things right.


http://specialtyz.com/blog/?page_id=178

[michael everson]

If the clearance in the slave cylinder was the issue he would have the opposite problem. Clutch would be slipping all the time. Sounds like you master might be too small. Works ok when everything is cool, but once things heat up the travel might be marginal to get everything to work.

Another thought. I wonder if you have a bad input shaft bearing in the crank shaft. Maybe that's is binding when it gets real warm.
Mike

[scottiec]

I wonder if you still have air in the clutch master. May need to bleed that.

[CraigS]

Insufficient clearance at the MC/pedal pushrod? Over filled MC reservoir?

[Slider]

If the clearance in the slave cylinder was the issue he would have the opposite problem. Clutch would be slipping all the time. Sounds like you master might be too small. Works ok when everything is cool, but once things heat up the travel might be marginal to get everything to work.

Another thought. I wonder if you have a bad input shaft bearing in the crank shaft. Maybe that's is binding when it gets real warm.
Mike

Mike, thanks for this feedback. the part that confuses me, is that for the first 2 years, there was NO issue whatsoever. Same master cylinder, everything. Then all of a sudden this started happening, and then once I would adjust the rod, it would work for awhile, to the point where it worked for about a year and 500 miles and then just started again a couple of weeks ago. Of course, it could be that the Master Cylinder is too small and I've just been masking it with my modifications to the push rod...

It seems like something went bad somewhere along the way... hadn't considered the release bearing...

I think I will try to bleed the clutch again. Does anyone have a process that they are fully confident in? I've done what I believe to be correct, but perhaps I'm just not doing it right. That would be the simplest answer to this issue.

[Slider]

Thanks Scottiec. I'll try it again.

[Mountain-Metalworks]

From all the bleeding you've done I'm guessing most of the hydraulic fluid has already been replaced, but I'd make sure 100% of the fluid is fresh. And don't use an opened bottle of fluid, get a brand new one. If you're using DOT3 brake fluid it is hydroscopic and absorbs water over time. Water in the fluid, when it accumulates and becomes hot, will turn to steam which is more highly compressible than the fluid. This could explain why it happened over the course of several years, and only happens when it's hot.
You may even want to completely drain the existing fluid and starting over. This means you'll have to bench bleed the master again(you can do it in the car...), but it would be better than adding good/fresh fluid to bad fluid and again letting some H2O in the system.

Good luck!

-TJ

[michael everson]

I always just gravity bleed the hydraulic clutch. never had a problem. Just open the bleeder and let it run out Make sure you keep the resiviour topped off. I wasn't talking about the release bearing, but the bearing in the end of the crankshaft.

Mike

[scottiec]

I always just gravity bleed the hydraulic clutch. never had a problem. Just open the bleeder and let it run out Make sure you keep the resiviour topped off. I wasn't talking about the release bearing, but the bearing in the end of the crankshaft.

Mike

I believe the pilot bearing

[karlos]

From the link posted above: "If you are experiencing a new clutch slipping or if the pedal height changes as the clutch heats up, then the free play has been removed." So yes, clutch slippage is a symptom of insufficient freeplay. And when coupled with heat expansion of the fluid that prevents the fluid from returning to the reservoir, you'll also experience the opposite problem - inability to fully disengage the clutch.

Pretty common problem with an upgrade to a performance clutch. As compared to the OEM clutch, more travel is required to disengage the performance clutch. This leads folks to adjust the pushrod to make it longer. If all the freeplay is removed there is the potential for the piston in the master cylinder to be pushed past the port that opens to the reservoir. This means that it cannot release pressure in the system. So the clutch slips while at the same time cannot be disengaged because, once the port is blocked, no additional pressure is generated by pushing the clutch pedal. The system works OK when cold but with the piston in the MC set so initially close to the fluid return port, the small dimensional change from heat-related fluid expansion is enough to push it over the cliff.

It may be possible to fine tune the adjustment so that there is maximum travel (longest pushrod) while still maintaining a small amount of freeplay when hot. The adjustment really needs to be made when the system is good and warm so you can confirm the return port remains uncovered when hot. If you are unable to get enough travel while still maintaining some amount of freeplay, than you probably have an undersized master cylinder.

My guess is that your system was marginal to begin with (meaning barely enough travel), you incurred some clutch disk wear over the course of 5200 miles that required a pushrod adjustment in order to get the clutch to fully disengage, and that in turn left you with insufficient freeplay that led to the heat-related problem you describe.

[srobinsonx2]

I am going to go all full nerd on the group. I am not an expert but I did stay at a Holiday Inn express last night. Seriously, I am an engineer and like to solve problems visually so I drew a little picture to help. Correct me if I am wrong but the only way the clutch could re-engage the flywheel is if the slave cylinder pushrod looses some of the force being applied to it?

http://thefactoryfiveforum.com/attachment.php?attachmentid=74001&d=1506102711

The slave cylinder pushes the clutch fork, which pushes the through out bearing forward which allows the clutch pad off the flywheel. Just a couple of thoughts:

1. Could the master cylinder have a problem (i.e. letting fluid back into the reservoir)? Maybe it isn't holding pressure.
2. I guess air could be in the system but you would think that would cause the problem all the time.
3. You said there are no leaks but couldn't that also cause this problem?

Again, no expert but I do like solving problems like this. Well, I like solving others problem. Not so fun when it is your problem. ;)

Good luck. You will get it licked. This is a great group of guys. Plus they are way smarter than I am so you should get someone on here that knows what is going on.

[GSides9]

My $.02 is a failing clutch master cylinder, but Mike Forte would be my first call. He is already involved since you mentioned his parts. No leaks, the hotter is gets the worse the problem, already replaced the 4 year old fluid, clutch hooks up fine- just doesn't release from pressure plate when hot. Compare your clutch rod travel, cold and hot, with someone else that is working right. I still think clutch master cylinder.

Glen

[2bking]

There seems to be some missing information such as clutch pedal position when the clutch force is first engaged and whether there is clutch spring force when the pedal goes to the floor. When I first started following this thread I was thinking it was a master cylinder problem but couldn't figure out why it only happen when hot. Perhaps it's the hot fluid returning to the MC that is thin enough to slide past the MC piston seals. If that is the case, there won't be any clutch spring force felt on the clutch pedal. If the clutch pedal is not coming out far enough to uncover the reservoir port, the clutch engagement point will be lower than when it's operating correctly. Perhaps there is a seal failure in the early portion of the MC travel that limits the volume of fluid pushed to the slave but only happens when the fluid is hot. This too will change the release/engagement point of the clutch pedal.

[Slider]

Okay, first of all, THANK YOU SO MUCH for all the great responses. I've had to travel for business the last few days and haven't had the chance to try much or think this through further. What a great community that guys would spend this much time offering assistance and even WHITE BOARD out the problem... for a total stranger! I think it is likely that I'll be responding with some questions, but for now.. Thank you.

[walt mckenna]

Your symptoms point toward boiling fluid from the fluid line being too close to something very hot.

[IslandVobra]

Is the fluid level consistent or dropping?
Check the back of the MC where the pushrod goes into the M/C and check for any fluid, sometimes there is a small leak out the back where it's very hard to see.
The internal M/C plunger seals could be going bad and bypassing fluid internally from the front to the rear of the seals or there could be pitting in the cylinder bore and allowing fluid to leak past it at certain points in the plunger travel, bleeding pressure off from the front to the back.

Put a pressure gauge on the lines and measure pressure cold and then hot to see if there is a difference.
Disconnect the line at the slave cylinder, cap it, and pressure test the M/C.

[KDubU]

I am going to go all full nerd on the group. I am not an expert but I did stay at a Holiday Inn express last night. Seriously, I am an engineer and like to solve problems visually so I drew a little picture to help. Correct me if I am wrong but the only way the clutch could re-engage the flywheel is if the slave cylinder pushrod looses some of the force being applied to it?

http://thefactoryfiveforum.com/attachment.php?attachmentid=74001&d=1506102711

The slave cylinder pushes the clutch fork, which pushes the through out bearing forward which allows the clutch pad off the flywheel. Just a couple of thoughts:

1. Could the master cylinder have a problem (i.e. letting fluid back into the reservoir)? Maybe it isn't holding pressure.
2. I guess air could be in the system but you would think that would cause the problem all the time.
3. You said there are no leaks but couldn't that also cause this problem?

Again, no expert but I do like solving problems like this. Well, I like solving others problem. Not so fun when it is your problem. ;)

Good luck. You will get it licked. This is a great group of guys. Plus they are way smarter than I am so you should get someone on here that knows what is going on.


Like!

[frankb]

Slider:

Have you noticed a difference in clutch pedal effort since this started? Specifically, has the pedal effort decreased? If so, you may have a failed (or failing) pressure plate (diaphragm spring). If you can look into your bell housing (maybe through the release arm slot) and see the release fingers, are they all at the same height when the clutch is released? If not, this is an indication of a failed diaphragm.

Frank B