autoxer6

At a track day in my 04 Z06 this past weekend, I occasionally had a sticky clutch pedal. The car still shifted fine and everything seemed to work OK. It just seemed like the return force of the pedal was 1/3 of normal. Then if I pumped the clutch pedal once or twice, it was back to normal.

I flush my clutch fluid before every track day when I change the brake fluid.

Has anyone else experienced this? Is it something to be concerned about?

Thanks,
Chris Shay

davidfarmer

I've only had one car do this (out of about a dozen c5/c6's). Took the helper spring off of the pedal and haven't had any further issues.

DarkMastyr

Yeah check the helper spring as davidfarmer mentioned. It might be worn out. Or remove it entirely.

GettReal

my advice, do a search on here for "sticking clutch pedal" and you'll find more reading then you can handle... what HP are you running? Does it normally happen in 3rd or 4th at high rpm after running through all the gears to redline?

I removed the helper spring... did the "drill mod" did the "ranger" method" of fluid flushing and still had it happen. Only thing that finally got rid of it (for me) was a new clutch.. I tried an OEM one first but it did it again, I finally put in a centerforce and its been great since. Good luck but serious, the search will give you more perspective then you will get here in a single thread. there are TONS of threads going back years about this.

Steve

Ms Eliz

This same problem finally happend to me yesterday at Brainerd Raceway.
I change my fluid the "Ranger Way" prior to each track day and what a suprise this was!
I was shifting from 2nd to 3rd, hot engine, high RPM...it felt overly firm during pedal application then just sat on the floor until I did some fancy footwork. I backed off, did a cool down lap and it didn't occur the rest of the day.
Very concerning though.
Ms Eliz

Ranger

The root cause of pedal woes is a failure of the clutch hydraulics to maintain nominal pressure. This stems from disrupted seals in the master cylinder whose operation is impeded by accumulated clutch dust. A secondary cause of corrupt clutch fluid can be accumulated water. But far and away the biggest issue is clutch dust, which is produced in copious quantities on the track during up-shifts and down-shifts. The fluid swaps between sessions need to stay ahead of that accumulation.

If the clutch fluid is kept pristinely clean, pedal issues rarely occur unless the rated torque of the engine exceeds the rated clamping power of the installed clutch. In that case, clutch slip occurs under max load, producing excessive heat and prodigious volumes of clutch dust blown onto the throwout bearing, where it's squeeged into the fluid on each stroke of the actuator's main-shaft seal. That leads to irregular behavior of the hydraulics.

Details are here.

If a car exhibits clutch pedal issues despite pristinely clean clutch fluid, the next step is replacing just the master cylinder. Thereafter, keep the fluid clean to protect the seals.

Some owner pride themselves in running satisfactorily with corrupt clutch fluid. But few of them ultimately avoid pedal issues.

For reference, I have driven five different Z06 to 85K street miles, 700+ drag strip passes and 150 HPDE laps without any clutch pedal issues. Clean clutch fluid and appropriately sized clutches are the reasons I've avoided the pedal woes that afflict others.

Ranger

sothpaw2

I've band-aided this problem by going to Castrol brake fluid, it has a much higher wet BP than even Motul 600RBF. I would suggest to the OP to change to the Castrol (6-8 fluid swaps) as a temporary fix and then maybe try changing the clutch master cylinder (since you can't really get to the slave!). Of course this assumes the fluid was clean in the beginning.

Ranger

Master cylinder replacement. Parts about $150. Good tech can do the swap in about an hour. Requires removal of left-front wheel and opening the fender liner.

Ranger

trackboss

I think with the factory bleeder it will take a lot longer than that. I don't even think I can get my hands in there. Why on earth gm didn't install a bleeder somewhere more easily accessable I have no idea.

ajg1915

Hey Ranger,

If the hydraulic system is functioning properly, no leaks, how does clutch dust get into the system ?

You don't hear about brake dust getting into the brake master cylinder.

I could see how some of the rubber seal particles could be in the fluid but not clutch dust on a properly functioning sealed system.


I can't reach it either and that's with the tunnel plate and exhaust out of the way.

stairman

It is a High RPM pressure plate mechanical issue.
If the pressure plate is pushing back against the slave cylinder that pedal is coming back up.
Good fluid will always keep the system in its best performance but it aint fixing the problem.

ryan0

taking off the spring and putting some heat shield between the block and the clutch/brake stuff cured mine.

Fastguy

I am about to swap a new master in since mine is doing the same thing.

drivinhard

Fresh fluid IS a must, as is a remote bleeder if/when you ever have it torn apart.

But I have personally tested bits/pieces (which requires much taking apart and back) to help isolate this problem. In one instance (on my car), changed a stock Luk/GM LS6 assembly, for another Luk/GM LS6 assembly, and re-used the slave and master (and bearing) only replacing the fluid, and got a sticking pedal right off the bat at high rpm. Never had that problem before with the old hardware. I purposely changed the clutch that time, in this fashion, to limit the variables.

I have felt the pedal get spongy at the drags when hot lapping (and also at a few open track events), and that's fluid. My current 01 does not have a remote bleeder, it's going on with the new clutch after RA in Aug.

Changing the fluid thing is good advice/good practice, but it's not the sole problem.

Ranger

I can lead the horses to water, but some still refuse to drink.

It's a fact that clutch dust is entering the fluid in the hydraulics and accumulating there. How that happens is explained in the sticky thread and shown in the video. It also contains a link to the laboratory report that shown images of the clutch dust in the fluid.

I've done track rentals with drag racers for the past eight years. Our regulars all keep their clutch fluid clean via the protocol. They also have clutches properly sized for the power-level. None of them has suffered pedal woes through a combined thousands of passes.

The problem is some owners say they change the fluid, but do so very infrequently, and instead allow clutch dust to accumulate.

That dust (shards of copper and iron) attack the seals in the master and actuator creating wear points and micro leaks.

I've not spent much time on a road course, but while there I was swapping the fluid in the reservoir after every session. Result was zero pedal issues. But the clutch dust production was much worse on the road course than on the drag strip.

What the track rats with clutch pedal woes need to remember is the biggest issue in the clutch hydraulics is less about heat and more about accumulated clutch dust. Your fluid changing regime must stay ahead of the clutch dust accumulation. Once the master cylinder seals are damaged, no amount of clean fluid will cure them.

Ranger

Datawiz

My master/slave cylinders failed at 7,000 miles in my car. After the failure, I found your video. I change my fluid before each race. We're running 3 drivers in this car about 25 weekends per year. We've been good since the change, albeit, it's early. We might have 10 events on the car since the repair, but the fluid stays clean at all times. I'm counting on a healthy clutch.

Ranger

Good info, Datawiz. Looks like you're reaping the benefit of clean clutch fluid. Avoids needless clutch replacements and prevents the tranny damage that flows from missed shifts due to hydraulic issues.

Ranger

ajg1915

It's not that I don't believe you, but once you have passed a point (i.e. clutch dust ) in the slave, haven't the seals already been damaged ?

Your method may prolong period before either a new slave or master is needed, but ultimately a new slave and master are needed to eradicated the seepage of clucth dust into the hydraulic system.

Ranger

On a 6K shift (up or down) clutch dust is scuffed off the friction surfaces and blow at a speed of 45+ mph against the throwout bearing and exposed main-shaft of the actuator (slave). The next time the pedal is depressed and again released, the rubber O-ring seal squeegees that dust film into contact with the clutch fluid inside the actuator. That's how the dust enters the fluid. Squeegee action.

Once the dust enters the fluid, it remains in suspension so long as the fluid remains in movement. Once the movement ceases, the dust begins to precipitate out. If the fluid is not changed, the dust accumulates and creates an abrasive action against the internal seals.

As the owner/driver, you want to prevent the accumulation from ever occurring. Most, but not all, corrupted master cylinders can be rescued, unless wear points have already developed.

In short, clutch dust is unavoidable on C5/C6 due to the design. What is avoidable is allowing the dust to accumulate. Frequent swaps via the reservoir avoid that. So does frequent full bleeds of the clutch hydraulics. I have a remote bleeder but don't use it, because swapping the reservoir is easier.

Many of the trannies trashed on road course, drag strip and the street flow directly from clutch pedal issues, wherein the driver depresses the clutch and hits the shift, but the clutch never releases. Clutchless shifts at high rpm reek havoc with tranny internals.

So for $20 and 2-hours per year my clutch fluid swaps can save a racer a needless $2K clutch replacement and an avoidable $3K tranny rebuild. Seems like obvious preventative maintenance with a high return.

Ranger

gkmccready

So the real question for me is if there is an upgraded part with better seals available when I do need to do the clutch and whatnot?