Tony @ MPH

Looking for some advice on what to try next to solve my clutch hydraulics issue.

Here are the basics. Clutch operates fine for normal shifting pretty much all the time. On occasion however, when using the clutch for something other than normal shifting (e.g., feathering it to get the car to move slowly/precisely) the clutch will begin to act up and it is difficult to get the car into gear (or out of gear if it gets stuck that way). It *feels* like the engagement point is moved when the issue happens -- in fact I've had that actually happen, where the clutch will engage, but engages closer to the floor than it normally does. Most of the time, I'm just SOL and with the pedal bottomed out, it feels like the car is about to go into gear... but it just won't.

Sometimes pumping the pedal helps a little bit, sometimes not. In every case so far, the problem has "fixed" itself after a few minutes of not using the clutch.

For example, the problem happened several times at the track yesterday. Right after my burnout, after releasing the line lock, the car would surge forward and would get out of gear. But when I depressed the pedal again, it did not want to go back into gear. I tried pumping the pedal a few times and that didn't help, so I waited and tried again a minute or two later -- and it went into gear.

Shifting was a little soft after that going down the track (e.g., it was hard to find a spot in the pedal travel where I could always get the car out of gear and then back into the next gear) but the car DID shift -- just not in a way where I could really shift with a lot of precision.

When I replaced the clutch I did replace the slave but not the master. In the past, I thought that just bleeding the clutch helped the situation however I am wondering if it was the bleeding of the clutch or just the passing of time that helped things get better.

Any ideas on what to try next?

Skunkworks

Vague clutch pedal almost always with me was heat related. Although entrained air can also create allot of problems.

I assume you did drill mod… although some advise against it. To me drill mod helps but you can’t or shouldn’t side step clutch.

Does your problem occur after time i.e. after some hard driving?


Mike

Edit --- have you taken any heat precautions with hydraulic line?

Tony @ MPH

Yep, wrapped the OEM hydraulic line in Taylor plug wire sheath and then also put some aluminized velcro attached wrap around the plug wire sheath. It should not be getting "too" hot as far away from heat sources as it is.

There's an OEM spark plug boot that sits a few mm away from the exhaust manifold and is completely unprotected and shows no signs of damage. So I don't know if heat should really still be a concern.

Oh, also using Motul RBF which is supposed to have one of the highest boiling points of fluids out there.

Regarding when the problem happens -- no, it's not necessarily after hard driving. I had my car off in the staging lanes with the hood up and it had to get up to temp just before I went for my burnout. Immediately after my burnout I had trouble getting the car into gear. I don't think it could have heat soaked in the minute or two it took to get from staging to burnout to take off.

Also, the first time this happened was backing the car completely cold out of EG's back yard. I had to feather the clutch a lot to navigate around other Corvettes, people, and even a ditch. But other than that everything was normal and cool. Car would not come out of gear at all at first, then it did and we pulled it over and a few guys helped bleed the clutch from the top using a Mity Vac. Car immediately felt better and shifted but again, not sure if it was the change of fluid or the passing of time that restored the clutch.

Skunkworks

I assumed you performed all pertinent actions. I’ve been lucky and not had many clutch related problems after friend’s father (retired) fixes my screw ups.

It’s fairly obvious that clutch does not fully disengage all the time, so master/slave would be next logical place to look, followed by pressure plate. Any odd noises from throw out bearing?

Sounds like you exchanged fluids a few times so that’s likely not an issue. Since you replaced slave maybe master would be next step. Do you get much/any clutch chatter?


Mike

Tony @ MPH

No chatter.

I did kill one slave slightly when I first installed the clutch. Notice a lot of rattling on initial startup that eventually went away. When I opened it up the next time I found that the center plastic piece on the slave that keeps the TO bearing from moving around was chewed up somehow. I also heard the same sound on initial startup after installing the new slave.

Are you supposed to put a lot of grease on the face of the TO bearing? I wonder if it's binding somehow to the pressure plate fingers. This would explain the alignment piece of the slave assembly getting destroyed and could explain the odd hydraulic action as well.

peter pan

Tony, not sure if it is the master or not, when I fried my RPS clutch and replaced with the same clutch you have I also put in a new slave and master and this was at approx 6k, the slave for sure was hosed. After break in the chatter for me is mostly gone and I can no take off mostly normal and have had zero shifting problems. I know someone else mentioned the shifter, not sure here, I use a hurst, so I suspect it to be a master cylinder since that is the only thing that is not new in your setup as you have bled and bled it so air is probably not an issue. Also I did not do the drill mod, good luck with the fix

gotjuice?

Steve, I think we just replaced the TO assy. The master cylinder we replaced with the RPS clutch. Tony, Do you still have the spring inside the car on the pedal assy? This could be an issue.

Tony @ MPH

Yessir, spring is still there. How does removing the spring help? TIA
(thanks in advance, not "This Is Africa".. hehe, just saw "Blood Diamond"...)

gotjuice?

I am not saying it would help. GM had an issue with people removing them. They said if you remove the spring, the system would not self bleed correctly. They reccommended not removing the spring. Steve's spring has been removed and no issues. I thought maybe you had removed the spring and It was not bleeding correctly. I guess that is not the problem.

Tony @ MPH

Bled from the top using a MityVac and got a tiny, tiny amount of air out of the system. Bled from the bottom using my remote bleeder and got no air but did get a lot of black fluid.

gotjuice?

I like to gravity bleed. It seems like it always gets all the air out and is very simple. I wonder why the fluid was black?

Tony @ MPH

I have been told that heat does this. There was a tiny, tiny bit of sludge in the reservoir but everything that came out of the hydraulics both through the top and the bottom was liquid.

I'm still at a loss as to why the fluid is seeing that much heat. All the lines are heat wrapped with the same stuff I wrap plastic with that runs closer to the exhaust manifolds than my clutch lines do... and the plastic is in perfectly good shape. The boiling point of Motul RBF is something like 550 degrees and I'm certain that the fluid can't be seeing more than 200-250 degrees from heat from the turbos based on distance from the heat source and the heat wrap.

Thanks for helping keep this thread afloat and for the info/discussion I really need to get to the bottom of this issue and am surprised there are not more people here who have experienced this or know the solution?

Someone save me before I go get the inside of my bellhousing coated with Swaintech thermal barrier

Skunkworks

All it takes is one hot spot to boil fluid as it does not recirculate. Again not a clutch expert as I have my transmission work done by other person (a hobby of his).

I have in the past replaced numerous slave cylinders with complete fluid changes and improvement was marginal at best. I then did master and difference was night and day. Symptoms were similar to yours but manifested them selves noticeably after hard driving.

Also I had a clutch in the past that would slip ever so slightly on hard shifts and would also get mushy over time (hard driving). I don’t think this is your issue but fluid was very burnt when replaced.

I’ll ask tomorrow as he builds transmissions for street and race cars.


Mike

Boob

I would look to the master cylinder. Try the McLeod Master cylinder. It's a much better piece that OEM.

My stock MC failed and was giving me all sorts of pedal issues due to internal leaking. Replaced w/ McLeod and she's running pretty well now.

Tony @ MPH

Well the MC is the one thing I have not replaced in the whole clutch system. I think I may try that before paying for someone to open up my drivetrain and take a peek. I am just not in the mood to take the car apart myself for another slave at this point.

Boob

Remove your wiper fluid tank when you replace the MC to make it SO MUCH EASIER.

Also be sure you bench bleed the crap outta the new master cylinder. Again I reccomend the McLeod unit, but that is just personal experience/opinion.

jmiller

I had a similar problem with my m/c, and a new oem fixed my issues. (at least until my slave died about 4 months later)