gdouglas

My 2013 ZR1 clutch pedal acts weird when the engine is revved over 6,000 rpm more than a couple times. Not even tracking the car but driving in a "sporting manner".. Pedal goes to the floor, barely engages or disengages the car, etc. The info I've found states that the slave cylinder is inside the bell housing, where things are hot...duh! And that's what is causing this problem. On line sources suggest changing the fluid, getting high performance fluid, etc. I've flushed the system twice - from the top by sucking out the fluid. The bleeder valve is on the slave cylinder. You have to take the car apart to get to it. Has anyone relocated the slave cylinder? What's a permanent fix for this problem? I know people track their cars. How do they deal with the clutch problem? Thanks in advance. -Gordon

Texasthunder

What color is the master for the clutch?

gdouglas

The fluid is clear but becomes a little discolored after use.

gdouglas

I'm using Dot4 fluid. It's clear and becomes a little discolored after use.

Texasthunder

I'm talking about the color of the fluid reservoir on the master. Old style is white and the new style are black. If the slave is not leaking and you have the white reservoir on the master cylinder I would replace it. The white ones are a known problem.

Apocolipse

Slave doesn’t give a **** if it’s hot or not - that’s a myth unless you are running junk fluid that is boiling.

Willing to bet your return spring is snapped - look under there and see if it’s broken. Typical cause of pedal hang since the return port doesn’t get uncovered unless the pedal is all the way up.

1SLO2OH

Like TexasThunder mentioned, you likely have the original master cylinder. There is an updated part from GM that will likely fix what you are experiencing. The easiest way to tell is by looking at the fluid reservoir to see if it is the new or old style.

_zebra

and if you do end up working on the slave, do yourself a favor & install a remote bleeder line (preferably with a speed bleeder screw).

BlueDevilZR1

Another vote for the master cylinder and reservoir. Mine was doing all sorts of weird stuff when I first bought it. I ended up ordering a new master from GM (comes with new reservoir) put it in and the clutch pedal feels night and day better and is 100% consistent like it should have been from the start.

Chevy Cust Svc

This is not the Corvette ownership experience we strive for. Our team would like the opportunity to learn more about the clutch concern on your ZR1 and investigate ways we can potentially assist. When you get the chance, please send us an email to socialmedia@gm.com. Be sure to include your Username and Forum name in the subject line, then provide additional details about your experience in the body of the email. We look forward to your contact.

JABCAT

If the pedal sticks to the floor it's the master cylinder. There was a 10-yr/120k mi extended service to replace that with the updated part. The updated part is 19331709 & costs a little over $100.

JABCAT

If the pedal sticks to the floor it's the master cylinder. There was a 10-yr/120k mi extended coverage to replace that with the updated part. The updated part is 19331709 & costs a little over $100.

corvettejoe09

"Aftermarket clutch is the only fix" by Lights ZR1

This statement is totally faults & couldn't be farther from the truth!!!!
When I got my ZR1 over 10 years ago, the pedal would stick to the floor occasionally just like my previous C6 Z06.
So I did a lot of research back then & decided to go with the Tick clutch master cylinder.
I've done about 10 years of HPDE. Pushing the car 8/10th to sometimes 10/10th on road courses, it's the ultimate test.
Driving on the public streets don't compare to road courses for testing the Tick clutch master cylinder. I had zero issues.
Back when I changed over, GM didn't have an upgraded one. I've read on this forum that some still have issues with the upgraded master.
If the above quote was true, I would still have issues because I didn't replace the clutch with an aftermarket one.

corvettejoe09

Also, when shifting from 2nd to 3rd at high RPM, some times I would miss the shift.
Like I mentioned above, replaced the OEM clutch master cylinder with a Tick & had zero issues with the pedal on the floor or missing a shift ( over 10 years now).
And that is without replacing the clutch with an aftermarket one.

_zebra

not necessarily.
the F-body problem was primarily due to the clutch line between the master & slave having a build-in restriction that, when drilled out to nearly the inside diameter of the braided line itself (i.e., the "drill mod"), fixed the issue of not having enough return pressure for a proper 2-3 shift after a launch.

i understand the C6 ZR1 problem to be a master cylinder design flaw.

Tahoe

GM specs Super DOT 4.......higher boiling point & more frequent fluid changes.

Lights ZR1

I’ve made a discovery. This could be something, could be nothing.

OP if you are still reading this thread, if you replace your master with an updated 19331708 GM unit or Tick Master Cylinder, this info could help. It’s very hard sifting through what’s right and wrong on these forums and sometimes you just have to try stuff yourself.

Some people claim the clutch is self bleeding, and this quite simply does not appear to be the case. I’ve had air in mine for THREE YEARS and possibly longer! When you swap master cylinders you most likely WILL get air in the system. You WILL need to bleed properly, period, if you got air in the system. You may also have no issues, and that’s fantastic if that’s the case. Pedal pumps do not get it out. Ranger method doesn’t bleed anything. And sticking a vacuum onto a Katech remote bleeder as it’s shipped is worthless, nothing gets displaced because of the swivel letting in air! 90+ seconds to empty the reservoir is worthless. And if you try to bleed the Katech line as shipped with the pedal you will end up with a massive puddle of brake fluid. Swivels don’t seal unless they are tight!

Did some testing once I got the Russell 641370 fitting onto my Katech remote bleeder line. I went to bleed the system with pedal pumps and air came FLYING out the line. 3 large bubbles right off the bat. The only time air was introduced to my system was 3 years ago when the updated master was installed, perhaps from the remote bleeder install, and possibly when I overfilled the system from Ranger method and my pedal issues started. It’s quite possible air got in before this, again around 3 years ago, as I originally found my reservoir pitch black and barely on the minimum line. Overfilling the reservoir perhaps over pressurized the system and moved the air since the bite point massively moved? Maybe air got in because the level was too low before that? Not sure. Perhaps air got in from the remote bleeder install as all the fluid came out of the reservoir and the lines when I undid the bleeder screw? Not sure. All I know is the dribble fluid flow out of the Katech bleeder with a vacuum wasn’t displacing air, when it was just sucking in air from the threads instead of sucking fluid through the line.

Anywho, three pedal pumps up and down takes the reservoir down to the minimum line. Fill and repeat as much as you want.

Ever since doing this, I never had the courage to test my clutch. I had been just cruising. I finally did yesterday in 100 degree temps after being heat soaked. 1-2-3-4 shifts absolute BUTTER and NO STICKING SOFT CLUTCH (I have the Lingenfelter return spring and it’s obvious when the pedal goes soft). I hear more drivetrain noises when I actuate the clutch if I’m not super smooth, a snappier clutch engagement, and overall a better pedal feel. Previously, the clutch would get upset with one single redline trip and would be noticeably softer. I also have no assist spring installed. This has never been from boiling clutch fluid. I used the ACDelco DOT4 fluid specified in the manual, which is made in Germany by Pentosin and is low viscosity for better flow. Your mileage will vary.

I reached out to a guy on YouTube I’ve been watching for over 10 years. You can find him by the name Corey W. He has never had an issue with his factory master cylinder on his ZR1. He’s done all sorts of track days for many years on various tracks, mainly Circuit of the Americas. No sticking pedal, nothing! But his previous 08 Z51 did. I’ve run into others with similar experiences. It’s all very confusing as it’s clear the root cause can vary car to car!

Factory fill is low viscosity DOT4. Anything like that should be good.

gdouglas

I'm finding that out, Lights ZR1. One person does one thing that works and someone else says that didn't work for them. I have the upgraded "black" master cylinder made by AC Delco, and a date to install. I'll start with that and see if it works. More to come.

Lights ZR1

I completely agree. I have found out the hard way what works for one person may not work for someone else, and may have lost my best friend over that argument. It is what it is. Been sick a week over it.

Take the clear reservoir off the old unit and swap it onto your new updated master cylinder so you can see the fluid. It’s just a simple hose clamp. I did not do this 3 years ago and regretted it. I found a NOS clear reservoir by itself and ordered it a few months back and installed it. 19208899.

If you are able to properly bleed the system after changing the master cylinder, definitely go for it. My experience suggests that if air gets into the lines you aren’t getting it out with pedal pumps. Your mileage may vary. Let us know how it goes, good luck!

I also figured out that 19331708 and 19331709 are identical. Both have an inner bore diameter of 0.55 inches or 14mm per GM’s own parts catalog. Identical pushrod lengths as well of 6.52 in or 165.67 mm.