My 99 C5 6-speed clutch is continuing to give me problems, and it is getting worse.
The pedal sticks to the floor, but I can stick my foot under the pedal and it "pops" up and works fine until it sticks again (more and more these days, especially more before the car warms up).
The clutch started sticking a few years ago, but only occassionally, typically at stop lights if I held my foot on the clutch for a longer period of time.
Back then I checked the forum and it said to start changing out the clutch fluid in the reservoir, so I did every couple of weeks until it changed from being dark to more clean. (I used the Prestone dot 4 synthetic that was recommeded in the post).
But that hasn't fixed the problem, I am actually concerned it may have made it worse...
My dad has a 2006 C6 6-speed, he has been using the same fluid to "flush" out his reservoir, and when he took it into the dealer for something else they said they had to flush out all his clutch fluid because he was using the wrong fluid and it was screwing up his seals, etc.
Is there any chance using the prestone fluid has casued the problem to get worse on my car... if so what will I have to do to fix it?
The problem feels more physical, like there is a hinge in the arm for the clutch pedal that is sticking and then pops up.
Is there anything else it could be other than the wrong fluid messing up the seals... something that can be adjusted, lubricated, etc.?
Thanks for any advice or thoughts you have.
(accidentally posted in C6 yesterday)

 

You do not say how many miles on the car or if you have ever had a new clutch put in the car. Is the clutch fluid at the right level in the reservoir? What color is the fluid? Get the car up on some ramps or a lift and inspect the lines and bell housing for any fluid leaks. Check the clutch pedal return spring to make sure it is not broken.

DOT 4 should not cause any issues with your clutch, simply has a higher boiling point than DOT 3. If you are using the Ranger method to change out the fluid, you need to suck all the fluid out of the reservoir, add new fluid up to the step and then pump the clutch pedal about 40 times and change out the fluid again in the reservoir repeating these steps until the fluid is clear. It may take you five or six cycles before the fluid clears up. This should also help remove any air in the lines if there is any which could also be contributing to your issues.

Other potential causes are a bad slave or master cylinder. If flushing the system does not resolve the problem, you might have to bite the bullet and take it to a shop who can do a thorough inspection and diagnose the problem. Good luck with it.

 

These cars are really good at giving us a warning of impending failures and sounds like your's is doing just that. Time to take it in and work the issue rather than dragging things out till it fails. You can replace the master on your own and if still having an issue, then you'll need to drop things out so you can get to the slave but since it'll be apart, might as well replace the clutch, pilot bearing and rear engine oil seal at the time.

 

When your pedal sticks to the floor does your clutch remain disengaged or is it enaged?

If the pedal stays on the floor and the clutch is disengaged, it's likely a weak pressure plate. That was a problem I had with an M6.

If the pedal stays on the floor but the clutch is engaged, it's a hydraulic issue - master or slave or maybe even a bad line with a plugged restrictor.

Once you get to the point you believe it's the slave, it's clutch replacement time because of the work involved in getting to the slave.

 

The other postings give you some good info and suggestions. Here are a few added things and a list of potential causes:

 

Unless you FLUSH OUT THE SLAVE CYLINDER,,,, you wasting your time.. TRUST ME on that one.

My ZO6 clutch gave up the ghost just like yours after I got past the 400 RWHP mark.

Thought for sure that the clutch was shot!

When I pulled it apart,,, BOY WAS I SHOCKED! The clutch disk, pressure plate and throwout bearing were in really great shape for 55,000 of very hard driving. I will say that the PILOT bearing was pretty much on its last legs (the grease in it was pretty hard and one of the needles fell out when I removed it)

ALL OF MY ISSUES were being caused by the damn slave cylinder. You would have been AMAZED at the crud and dirty fluid that I drained out of the OLD SLAVE.

The fluid in it contained a LOT of moisture. That right there will cause the issue that your experiencing. If the seal on the slave is weak and it sucks air back into the slave, it can cause the same issue. .

SO,,,,, that being said,,, I STRONGLY recommend getting you butt under there and BLEED THE SLAVE until that sucker runs clean. Its a pain in the ***** BUT,,,, if it works,, it beats the hell out of a clutch job!

The bleeding/flushing thing is NOT a 100% guarantee but, hell, give it a try.


If you do bleed the system,, you might want to consider installing a REMOTE BLEEDER while your in that area!

 

Now,,,, thats some very interesting info!!! Thanks Eric!

Bill

 

I have had similar issues with my Zr1 clutch that i had put it. It normally cruises around fine most of the time. Then when i get on it and run it through the high Rpms then it will hang half way. The clutch will be disengaged and the car is in gear fine i just have to stick my toe underneath the pedal and pull it out the final bit to be back to normal.

I have had the slave cylinder replaced recently and it still does it.

I have a remote bleeder on there as well and I have fully flushed the fluid multiple times.

I have used Prestone DOT4 or motul and similar results with both.

It's really frustrating that pretty much anytime i run the car hard I have to pull the pedal out.

Anyone ever had this problem and gotten it resolved.

Could it really be something like the pressure plate inside the clutch. I know its a heavy clutch, but it never did it on my stock C6 clutch, but the ZR1 replacement has done it consistently since.

Any help would be appreciated.

 

Thanks for all the replies... the car has just 41K Miles... and it still has all the factory clutch parts...

I will definitely re-flush the clutch reservoir using the "ranger" method, pumping it 40 times, etc until it is clean...

When the pedal is stuck down, the clutch is partally engaged... (I think)... I have been dealing with this for so long I have figured out how to work around it... I pull up to a light, push in the clutch and put it in neutral... right before the light changes, I depress the clutch, put it in gear, and when the light changes Itake my foot off the clutch and take off... after that I have to stick my foot under the clutch pedal and pop it up... then I am ready for the next gear change... if the car is cold I have to pop the clutch for each of the gear changes (unless I only depress the clutch pedal 2/3 of the way, then it pops up on its own), when the car warms up (10 minutes) it seems like it sticks less...

Thinking about it... if I were to sit at a light in gear and the clutch depressed, the car would try to creep forward or stall out if I hold the brakes down... if the car is in 1st gear I can pull the gear lever back to neutral, but if it is in reverse you cannot force it into neutral, you have to shut the engine off, pop the clutch, depress the clutch and shift it into neutral before starting it... hard to do if you are not prepared... I almost backed into something the first time it happenned.

I definitely want to also try bleeding the slave cylinder, see if that helps... I am OK with the pain in the ***** part... is there a post that describes how to bleed the slave cylinder?... if so please guide me that way...

thanks again everybody... I am keeping my fingers crossed, and will let you know how it goes...

 

Dont have a procedure other than what is in the service manual but,, you have to drop the midpipe, remove the tunnel plate and snake your hand and a wrench to the 11:00 poition on the front of the torque tube where you crack open the bleeder.

Other than that,,, its easy!

Service manual procedure:

Clean all dirt and debris from the clutch master cylinder cap to ensure that no foreign substances will enter the system.
Remove the clutch master cylinder reservoir cap with diaphragm.
Fill the clutch master cylinder reservoir with clutch hydraulic fluid GM P/N 12345347, GM Canada P/N 10953517, or equivalent, if necessary.
Raise and suitably support the vehicle. Refer to Lifting and Jacking the Vehicle in General Information.
Remove the catalytic converter. Refer to Catalytic Converter Replacement in Engine Exhaust.
Remove the driveline tunnel closeout panel. Refer to Driveline Tunnel Closeout Panel Replacement in Propeller Shaft.
Have an assistant depress the clutch pedal fully and hold.
Loosen the bleeder screw on the clutch actuator cylinder to purge air.
Tighten the bleeder screw.
Release the clutch pedal.
Repeat steps 7 through 10 until all air is completely evacuated. Check and refill the clutch master cylinder reservoir with clutch hydraulic fluid GM P/N 12345347, GM Canada P/N 10953517, or equivalent, as necessary in order to prevent air from being drawn through the clutch master cylinder.
Fill the clutch master cylinder reservoir with clutch hydraulic fluid GM P/N 12345347, GM Canada P/N 10953517, or equivalent, if necessary.
Install the driveline tunnel closeout panel. Refer to Driveline Tunnel Closeout Panel Replacement in Propeller Shaft.
Install the catalytic converter. Refer to Catalytic Converter Replacement in Engine Exhaust.
Lower the vehicle.

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Document ID# 676814
2001 Chevrolet/Geo Corvette

 

I went 50K miles on stock clutch (with no pedal spring either) with not 1 problem of pedal sticking or master problems and I had never began replacing master fluid until about 40K and when I did it was like tar in there. I drove the car like I stole it also and gave that clutch a helluva beating. I upgraded clutch when supercharger went on and used existing stock master and never had sticking problem either with it. I believe it is strictly a pressure plate problem with these cars when it happens. I'm using a twin disc now with a new stock master (original one had a slight internal leaking seal so replaced it) and still no pedal spring and all is fine for last 18K miles.
I personally think the spring really doesnt do much of anything even though designers say it does and is more of a old lady leg cramp helper. My pedal is at the very top always without it anyways and always has been. Maybe some pedals hang lower or people ride the pedal and this causes some problems I dont know, but in all my 68K of driving never had a spring and never needed one BUT if it floats yer boat leave it in..

NB 99, you might have a slight internal clutch master seal leak like I did when I put a twin disk in. It kept clutch from disengaging just barely and some shifts were slightly hard to do wot. I replaced with a stock GM master and all was fine again. I seemed to damage a internal seal when way too much vacuum was applied with a Mity Vac pulling fluid thorough a remote bleeder.

 

Bill, I just wanted to make sure... the procedure you were quoting from the service manual, was instructions for bleeding the slave cylinder, right?

forgive me, I know the slave cylinder is part of the clutch system, and I assume it is fed by the same clutch fluid reservoir as the master cylinder, I just wanted to make sure.

thanks again

 

YES! Its the same info for 97 - 2004 and is for the TOTAL system connected...

You can NOT bleed the system without having it totally connected (slave & master).

BC

 

thanks to everyone, especially supercruz and Bill C...
Before jacking the car up to begin bleeding the slave cylinder I decided to pump up the clutch using the "ranger?" method (changing out the reservoir fluid a few times) even though my fluid was clear...
In the past I had just changed out the fluid in the reservoir and then drove it for a few days and repeated...
this time I pumped it 50 times... and amazingly (to me) I noticed a difference...
so I changed the fluid (still clear) and pumped it 100 times, then repeated several tiimes...
after about 4-5 times I noticed a little discoloration, and did it 2 or 3 more times...
It is 99% better, so I will see if this fixes the problem... if it comes back I may still have to break down and bleed the slave cylinder as Bill described.... but I'll keep my fingers crossed this did it...
thanks again!!!

 

well, I thought I had it fixed... but when I went to drive the car to work a couple days later, I pushed the clutch, and it stuck to the floor again...
it was weird, when I popped the clutch pedal up I noticed something:
if I pushed the clutch pedal down about a third of the way and then took my foot off the pedal, it actually would go down on it's own, down to two thirds of the way down...
has anyone heard of the pedal going down on it's own like I described ???

I tried pumping the clutch to get some pedal back... it took a bunch of times but I finally got enough pressure in the pedal that I was able to "pump it up"...
as I drove it into work, the pedal would get a little worse, so I would pop it into neutral and re-pump it up...
so it looks like I am going to have to do the service manual proceedure of taking off the Cat, etc, and bleeding the slave cylinder...

should I consider replacing the slave cylinder while I am down there doing all this work?...
how much extra work is it to replace the slave cylinder???

 

how does the dealership bleed the clutch system? do they have more than one method?
I had someone tell me the did not bleed it by taking off the CAT, plate, etc...
but that they use a vacuum system to suck out the old fluid using a pump attached to the reservoir cap...
the dealer that bled out my dad's C6 M6 did it for only $300...
so there is no way they are doing it by taking off the CAT, plate, etc...
I don't have the pump, so I will have to do it the hard way... I am just curious...

 

The master and slave is a closed system. I do not see how they can suck out anything other than whats in the reservoir cup.

IF,, your short on cash and want to attempt the repair, I would put it on stands, drop the exhaust, the tunnel plate and try to bleed the slave.

IF,, it still wont work properly, you can install a new master cylinder. Its not that difficult and may prevent you from having to pull the drive train to do a clutch/slave replacement.

My slave gave out yesterday. I installed a new SPEC clutch and after bleeding the hydraulic system and a few pumps, the master cylinder failed.


I'm replacing it with a TICK Master Cylinder

BC

 

#PIP3821B: Removal Of The Clutch Over Center Spring - keywords cylinder hydraulic master pedal - (Apr 15, 2008)
Subject: Removal of the Clutch Over Center Spring

Models: 1997-2004 Chevrolet C5 Corvette
2005-2008 Chevrolet C6 Corvette
Equipped with a Manual Transmission

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This PI was superseded to update model years and tac notes. Please discard PIP3821A.
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The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Condition/Concern:

It appears that some Corvette owners are removing or disconnecting the clutch over center spring on their vehicles.

This is not a recommended practice and customers should be advised of the implications of such an action.

Recommendation/Instructions:

The clutch master cylinder has a compensation port that is positioned within 1 MM of the top of the stroke. The compensation port allows internal pressure in the clutch hydraulic system to be exhausted into the master cylinder and also provides for system refill as the clutch disc wears.

One purpose of the over center spring is to return the clutch pedal to the very top of the stroke to expose the compensation port. The second purpose of the spring is to provide for the designed clutch pedal feel.

Removing or disconnecting the spring may allow the clutch pedal to hang in an at rest position with the piston short of the compensation port. If the internal pressure is not exhausted the CSC may get stroked too far and a clutch hydraulic system failure may result. The C5 clutch hydraulic systems were built by AP. The C6 systems were manufactured by FTE. Also, the pedal must be in the full up position, with the compensation port exposed, to bleed properly.

Anytime a dealer gets a hydraulic system complaint, the tech should inspect to insure that the spring is in place and properly connected. Related customer complaints might include poor shift performance, improper clutch release or transmission synchronizer damage.

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.

 

The clutch master is a short afternoon to change.
The clutch slave is a 3 weekend affair for a shade-tree part-time mechanic on jack stands. Not technically challenging just very time consuming.

As long as there is no fluid loss, you should change the master first. It's got all the classic symptoms.

Fluid loss from the bell housing means the slave is toast.

 

When I was at 400rwhp with the LS6 clutch it looked fine when I pulled it out after 5k+ rpm launches, but it still stuck to the floor.

Just because a clutch has plenty of material left on the disc doesn't mean the clutch still has full holding capacity. The diaphragm springs like any spring can get weak over time from usage and heat along with the friction material being glazed.