joemoia

Wednesday at WSIR I started experiencing the "stuck clutch pedal" syndrome. It would stick to the floor when I was braking/down shifting with a clear track ahead; when I was running behind slower traffic The clutch pedal would work fine. The clutch (Luk pro gold) and Z06 clutch hydraulics are new (installed Jan '07) with only about 5K total mi./12 trackdays on them. I ran the original harware 4 yrs./50K mi./45 trackdays and never had a problem (fluid in the reservoir was changed once). I had the new clutch hardware installed more as a preventative measure in conjunction with other work (H/C upgrade and a new diff) being done at the time. I didn't think I would be creating a new problem

After doing a search in C5 tech it appears there are only 2 remedies to the "stuck clutch pedal" problem (assuming the clutch itself is OK):

1. Bleed/replace clutch fluid, and hope

2. Replace slave cylinder, and hope

I do have a remote clutch bleeder installed so bleeding/replacing the fluid is relatively easy and cheap. Is there a "preferred" fluid people use or is any DOT4 brake fluid acceptable? I use Motul 600 for my brakes. How often do you guys bleed/replace the clutch fluid?

Reading the C5 tech posts it also appears that the OEM slave cylinder design is the real issue. Even if you replace the slave cylinder it doesn't mean that problem won't re-appear in a short period of time. You may get a good one like my original, or you may get one that acts like my replacement. Is there an aftermarket replacement which will provide reliable operation over a long period of time?

TIA

Joe M

Last C5

A few people have reported an improvement/cure by simply removing the clutch pedal assist spring. You cram yourself in the footwell and have somebody with a stick or whatever hold the clutch down while you slip the spring off it's posts. You will feel a slight increase in pedal pressure but nothing that's distracting.

I drain, clean, and refill my clutch reservoir before every track day with ATE type 200. Good luck with your dilemma.

fatbillybob

Is your slave external to the throwout bearing or do you have a slavecylinder that is one with the throwoutbearing?

99BlackZ51

I just experienced that problem for the first time last weekend at the June Sprints. At high RPM's the clutch would not disengage and the pedal would stick, I tried the fluid flush and bleed but no help. Fortunately the GM Performance Division truck was there for race support. When I presented the problem to them they told me they were already working on another T1 Vette with the exact same problem and both of us had installed a new GM Z06 clutch set w/slave over the winter as a preventive measure. For some reason the slaves were not traveling the full 10mm like they were supposed to and the engineer was thinking they had a bad batch of slaves ship out since the Phoenix guys have reported problems with them lately also. There may also be pressure plate related issues so they changed everything out for me and got me out just in time for the race.

They said they were going to install my old parts on a test car and run it at Milford to see exactly what the problem is. They are also sending me replacements for all the parts I had to buy to fix the car, which I though was pretty cool!

While diagnosing the problem they talked to the engineer that designed the clutch system. He said they are thinking about eliminating the bleed valve on the slave since they stopped bleeding it on the assembly line. Both the master and the slave are prefilled with fluid and once connected only require a few pumps of the pedal to bleed. If additional bleeding is required it can be done with a vacuum pump at the reservoir.

I would recommend removing the remote bleed line since it is a potential source for leaks and reinstall the stock bleeder and bleed through the reservoir if necessary. It is also important to use high temp brake fluid in there.

I hope this helps,
Scott

joemoia

fatbillybob - I don't know, the shop replaced the original master/slave cylinders with new OEM ones.

99blackz51 - thanks for the response and info. If you get any further info from GM Performance on the slave cylinders please let me/us know. I guess I'll be in the "bleed/replace fluid and hope" mode for awhile, I can't afford to keep having to replace slave cylinders until I get one that works

Cobra4B

Periodically suck ou the fluid w/ a turkey baster and remove the clutch spring... it works.

fatbillybob

Well if there is no factory aftermarket solution then you need to make one. The problems can be either weaky designed system and or over load of a marginal ssytem with a heavier pressure plate which is often used as a "upgrade" in the clutch system along with sometimes changing from organic plates to kevlar etc... If you have an external slave the problem can be solved easier by sending the slave to white post in virgina. They can resleave and reseal a slave cylinder like they do on antique cars. You need to ask them to not just put new seals in but that the design is such that you are blowing out the seals and you are failing to get full slave cylinder travel. They will resleave and use a different seal shape/size to keep your slave cylinder working to handle increased pressure loads. If you have an hydralic annular throwout bearing with integral set of seals that travels on a shaft this can be fixed too by white post but you need to send them the shaft and the design may or may not be so easy or cheap. For all we know stock componants may be designed to the limit and track driving, more heat capacity in kevlar discs, more pressure on pressure plates will the find the next weakest link and in this case it is the slave.

Joe_G

I turkey baster my clutch master using Motul 600 before each event, road course or drag strip. Only time I've ever had a bad pedal was the time I forgot to baster before the event. It's certainly cheap and easy to try before moving on to more expensive solutions.

beerkat

The first time that I tracked my car, '01 ZO6, I had the issue of the clutch pedal not returning, sticking to the floor. I was shifting between 6,000 and 6,500 rpm. I now shift between 5,000 and 5,500 rpms and have not had any problems with the clutch sticking to the floor.

Ranger

The place to start when pedal woes surface is getting the fluid in the clutch hydraulics back to the nominal dry boiling point. For good fluids of DOT4 or Super DOT4 type that puts the boiling point at around 500F.

Conversely, fluid degraded by moisture and heat cycles will boil at 300F or less.

That's important because the concentric slave cylinder is inside the bell housing, a cauldron at race speeds where high-rpm up-shifts and down-shifts produce substantial friction-produced heat.

If the fluid in the slave boils, pedal woes follow. Same mechanism at play that requires bleeding of the brakes.

I don't road race or autoX my Corvettes but I do drag race them. Since developing the fresh fluid protocol, I've made 500 passes at the drag strip without suffering any clutch pedal issues. And I have cured pedal issues on countless fellow racers' car but cleaning up their clutch fluid between passes.

Here is a write up. Taking Care of Your Clutch

Finally, GM LS-X motors have had a high incidence of clutch pedal issues since 1997. It includes Corvettes, F-bodies, and even the GTO and CTS. What they have in common is a concentric slave cylinder inside an unvented bell housing where aggressive driving (launch and shifts) can bring temps above 400 degrees. Degraded clutch fluid doesn't stand a chance at those temps.

Owners who keep their clutch fluid fresh have an extremely low incidence of pedal woes.

Ranger

Olitho

Well that settles it Joe. You are going just too plain fast!!!

I hope my clutch starts acting up soon, too!!!

99BlackZ51

I have seen fluid cause this type of problem on other Vettes and helped them fix it with a flush and bleed but that was definately not the problem in this case. When I depressed the pedal the clutch did not disengage so removing the spring would only help the pedal come back up.

They said they changed the supplier for the slave castings recently so that may be the problem. Hopefully I will hear something from them soon, I will post as soon as I do.

Scott

96LT1

Check out the following link...

http://www.chevyhiperformance.com/howto/39021/

The problem caused by the restriction in the line is most of found by drag racers. From what I have heard it can effect road racers as well due to the fluid being 'held' near the heat source. It might be worth while to drill out the restriction to see if it helps fix the problem.

Ranger

The "drill mod" to the master cylinder hydraulic line is pretty much an "F-Body" approach. Hasn't worked on Corvettes.

I've tracked the "pedal woes" issue for six years. The Chevy explanation...bad parts...lacks credibility since woes attack thousands of LS-X cars across multiple platforms since 1997 without a "parts solution." What the victims have in common is nasty-azzzed clutch fluid and high temperatures at the slave from launches and/or high-rpm up-shifts or down-shifts.

Road racers know to bleed the brakes because high-heat cycles cook the brake fluid. Why should the brake fluid in the clutch behave differently when subjected to the extreme temps inside the caldron called the bell housing during race conditions or aggressive street/strip driving?

Ranger

Bill Dearborn

I have been running C5s on road courses and autocrossing with them since 97 and have never had a clutch pedal problem. Currently I am running a C6 Z06 clutch in my C5 Z (installed when the original started making loud noises). It has been in the car since Oct. 2005 and I haven't changed the fluid yet. When at Watkins Glen I usually have 3 high rpm upshifts per lap while getting close to the rev limiter 7 times per lap. The car gets very hot doing this for 30 to 40 minutes at a time. Never had the clutch stick once in 10 1/2 seasons. If this problem is due the clutch fluid being hot, dirty with a lot of moisture in it then it should have happened to my cars. I don't think i ever bled the fluid in my 97 and I had it for 6 years. It also seems like I would have had the clutch stick when downshifting as the hydrualics do not know whether you are upshifting of downshifting. The problem has to be caused by something else other than the condition of the clutch fluid.

Bill

Ranger

Lot of opinions on the issue. Good to read yours.

Hundreds and hundreds of Corvette and F-body owners have cured pedal woes simply by cleaning up the clutch fluid and getting its boiling point back to nominal.

Also you may be interested to know that Chevy is now specifying Super DOT4 for all MY Corvette clutches, but leaving the brake spec at DOT3. Also Chevy is altering the long-term vehicle maintenance schedule to direct the clutch fluid be changed every 24-months. But they're continuing to state that the brake fluid never needs changing.

So, it would appear that Chevy is stepping up to heat to the clutch fluid being a root cause of pedal issues.

Ranger

joemoia

Ranger - when I did the search in C5 tech I read your posts and also your clutch write-up. If routine bleed/flush of the clutch fixes the problem, fine. I think I'll also insulate the hard lines for better heat resistance.

There were also some posts in C5 tech with results similar to Scott's above, in which bleed/flush did not correct the problem. I just hope I'm not in that situation. It will be awhile before I know for sure as I don't track the car during Jul/Aug months. It's just very frustrating that, like Scott, I replaced perfectly operating clutch components as a preventive measure, and now have introduced a new problem with the car.

Oli - It would be easier to accept if I were running sub-1:30 laps at WSIR!

Ranger

My point for six years of establishing and recommending this approach is that cleaning up the clutch fluid should be the first step in remediation of pedal woes. But in reality it should be part of any racer's standard PM activities.

Doing it via the reservoir is cheap, easy, quick and totally under the control of an owner without a lift or remote bleeder. But it won't solve every problem.

Most of those who say it doesn't work for them and whose cars I've looked at still had filthy, corrupt clutch fluid. When ask why, they generally say "it looks better than it did." Clearly the boiling point of the fluid was still compromised.

Racer don't run with compromised brake fluid in the brakes. Why accept the risk in the clutch?

Ranger

John Shiels

No brakes you hit the wall, no clutch you can't go

I never had a problem and I am lax on fluid changes for sure. I do need to follow it more closely.

Solo2GS

I have done the turkey baster/ vacuum pump trick quite a few times. Mine still sticks to the floor occassionally. Some times I have to pry it up with my foot and it pops back up, but you can tell the next time I press in the clutch it doesn't feel the same. It seems to take a bit to come fully back.

Seems that no matter how many times I replace it, I get more and more black goop in there!

I guess I am going to have to try that spring trick next. Anyone got a picture of it?