User Omega

Alright, I am looking for some help/advice here before I tear this thing apart making guesses. Sorry for the long post but I want to eliminate the 3892327 questions that could be asked here. I searched for a few hours but did not find an instance where this happened.

Info:

2008 Z06 619 whp

The clutch will not disengage. Here is how this went down.

The clutch setup is a Mcleod RXT stock MC stock Slave, Katech remote bleeder. MGW shifter Worked perfectly for 6.5k miles in car. 7k rpm shifts no problems or delay. No launches on the clutch and no signs of slipping or dragging. Before heading to the strip I replaced the fluid in the system. DOT 4 fluid as it should be. Drove the car over an hour to track again with no issues.

At the drag strip yesterday I launched the car 2 times. The first time I launched the car it went out a few feet and bogged with a 1.8 60 ft. I could not get the car into second gear so I aborted the pass. I depressed the clutch and put the car into 3rd an went on down. Seemed like I just missed the shift (has never happened before). I let the car cool waiting for the next test for 10.5 index. Second pass I launched the car a little higher maybe 6k and again could not get the car into second except this time I was unable to get into gear at all after leaving 1st. I had to rev match to get the car into gear.

At no point did the clutch smell, pedal feel change, or the pedal stick to the floor. Nothing changed except the fact that the clutch won't disengage.

With the car off you can go into any gear no problem so this is clearly not a shifter alignment issue. I let it cool and again ran fluid through the system. No air was seen leaving the bleeder with it buried in a bottle of brake fluid. I locked it down under the fluid and same result. Good pedal but it will not disengage the clutch. Pedal goes down with no feel change and comes right back up no problem with no delay as it did before. There are also no strange sounds or anything else odd that I can tell. I have pumped the pedal to hell. Let the car cool. I drove it home just rev matching (all highway) and started the car in gear to get rolling. I was hoping to regain clutch with the trip. I pressed the clutch a lot through the trip. No slip at all. Get home. I ran a whole bottle of Prestone Dot 4 through it. Again, no air and no change in pedal.


Could there be a bubble trapped in the system? Maybe I introduced when I replaced fluid before even going?

I had the car out in first thinking maybe I somehow fused the discs to the flywheel or PP but after romping it back and forth in 1st gear clutch in with no sign of breaking free or slip so I don't believe that to be the issue.

There is no fluid loss after pumping the pedal and I do not loose pedal feel if I hold it to the floor for extended period of time. Fluid pumps clean and clear through the remote bleeder no problem.

Could master cylinder be bypassing internally? Is there a way I can inspect the slave from under the car without disassembly to see if the slave is traveling properly?

MC and Slave were done with the clutch. I have also never let the fluid get nasty. The fluid has been a slightly darker color at best. The fluid was SRF for a while but a few thousand ago was swapped to RBF600 and had no issues from the change since that. I only changed because I didn't want to change fluid so often.


Any tests, ideas, past experiences,questions that may lead us to an answer before the guessing, or input will be appreciated. I have never had an issue where it didn't seem obvious what failed.

stefuel

Wait for someone who has one to reply but my guess is you broke something in the pressure plate or clutch disc. It's coming apart for inspection if it was mine. Brave soul driving it for a hour home without the ability to use the clutch.

User Omega

It may come down to a removal and inspect if I cannot get some ideas in here. I will probably attempt to get a scope in to see if the slave is moving properly or not before I do though. It won't be until later this week that I can get to it. Hopefully some ideas or experiences turn up here before that.

Driving it was meh. I have free towing and if started making noise or something awful I would have just stopped. After having just pushed it to 7k without it exploding I wasn't afraid of it. Other than not disengaging it serious drives, feels, and sounds normal.

Landru

Could be slave and/or MC has failed, what else could cause clutch not disengaging?

Before dropping rear for visible inspection perhaps replacing slave/MC, whichever's the cheaper of the 2 first, a reasonable approach?

HATE throwing parts at this stuff safe to say somethings failed in brake system, somewhere in circuit.
With this assumptions will only insure issue remains hidden.

G/L, confident you'll find it, ideally w/ minimal pain/$.
Please do follow-up, very interested what's behind this.

User Omega

I figured if the slave had failed it would leak. Is that not always the case? If so, what usually happens to the fluid be pressurized into it?

I could see the MC bypassing but I would think it wouldn't want to return. *I have removed my clutch pedal return spring. Definitely not loosing any fluid.

nuke61

I think you'd feel a failed slave or bypassed master, so I think it's a failure in the clutch itself.

spartan8270

Bad slave cylinder. Happened to me just like that!! Make sure you do a new slave and get the Monster Billet bearing support. That plastic piece is junk!

User Omega

So are you saying the plastic bearing support failed or the slave itself failed? If the slave failed then where is the fluid going that is being pressed into it?

To confirm here, you had good pedal feel with a bad slave or bearing support and no fluid leaks?

spartan8270

The slave failed internally and the pedal feel was normal. If youre going to pull it apart make sure you get a new GM slave and install the bilet support

MTPZ06

Sub'd

User Omega

I am beginning to think you are onto the issue here. I inspected the MC and found that I get no fluid pushed back into the reservoir when the pedal is depressed so I believe the MC to be good or at least not bypassing.

Not this weekend but next, I will hopefully have time to pull it and replace the parts. After researching the problem you describe, it makes sense to me that this would be the issue.




I will update the thread when I find out.


If anyone else has some input I am ears open until then.

User Omega

Small update. More to come either tomorrow or next day. I confirmed that the master is firm when uncoupled. No bypassing so I think it is safe to say its something inside. Still no leaks.

Sorry for the delay. I don't have much time in my schedule to get at it.

RamAir972003

Ok might be a long shot but I had a friend same issue the speed bleeder line was hot and was to close to headers which did cause the clutch to not engage to floor, might want to reroute bleeder line see if that helps or it could be toast.....

User Omega

The line is not leaking but I will check it out thoroughly. It could be damaged and me not know it. There are parts of it that aren't easy to see. It's about as far away from the exhaust as you could get right now. Even after completely cooling overnight and bleeding again, nothing changed.

stefuel

I retired from being a auto mechanic many years ago but the two related to this thread (clutch issues) stuck in my head and both of them I guessed wrong because you never know until you take it apart. Both clutched failed to release. I assumed both of them somehow fused themselves to the flywheel. The first one, a large chunk of clutch material broke off and wedged its self over good clutch material. So it was double stacked and the pressure plate could not open enough to provide slippage.
The second was even worse. The transmission input shaft friction welded it's self to a failed pilot bearing. Try pulling the transmission when that happens.

Schred86

i would put an inspection camera through the bell housing and check to see if the slave has any movement, or if something is blocking it from moving. If you can bleed the system than the master cylinder is working properly. Even with air in the system, you would still be able to disengage the clutch to get into gear.

I feel your pain, i had to drop my tranny after 1,500 miles when my speed bleeder was leaking where it goes into the slave. (i never grinded the casting marks flat). So if you need a slave i got one for ya cheap.

spartan8270

Slave cylinder is internally bypassing and not leaking. You'll need to yank it and might as well do a new clutch at same time as new GM slave.

FNBADAZ06

Almost sounds like the input shaft has welded itself to the pilot bearing in the crank shaft.
Did you replace the pilot bearing when the clutch work was done ?

Javvy

It could be as simple as the bearing support has disintergrated.

http://monsterclutches.com/billet-bearing-install

User Omega

I'm heading out to use an endoscope and see. Can you explain how it can internally bypass without leaking? I thought it was a single chamber in the slave. 1 way in and 1 way out.