Independent1

The air in the fluid suggests that either you are boiling the fluid or your system is not fully sealed and air is getting into the system.

Because you say your fluid looks clear and you are using a high boiling point fluid, I tend to think that somehow your system is getting air into it. Are you sure everything is sealed. What brand of remote bleeder do you have? I have heard that some of these leak. This could be the source of air.

Also, although not common could it be that either the MC or slave is defective? I know they are new but sometimes they have problems.

I think the pressure plate theory is interesting. However, when I owned my Z06 I never had a problem with the clutch pedal and I shifted at high rpm all the time. I hit the rev limiter more times than I care to admit.

LF97C5Vette

Was it modified? I never had problems until after i hit 400whp...

If the remote bleeder was leaking, wouldn't i be able to get air in the system just from stomping the pedal a lot? Or see at least some signs of leakage of fluid? That's not the case, I can't get any air in just by pumping the pedal. I even have a solid pedal feel, until I rev past 5.5k that is...

I really hope the Master and Slave aren't defective, I can't see any reason as to why they would be. The hydraulics don't act any different now than when I had the stock ones in.

Really, the Clutch is the only thing in the system that hasn't been removed. And while I hear that a lot of people have had success replacing the clutch, I'm still curious as to why that fixes it, and how i'm getting air in my lines...

I'm going to run it w/o Cats this weekend, after flushing the fluid again, and heat wrapping/shielding everything that makes sense... I'll post again if i see any results.

After a flush, I get about 5 minutes of high RPM flogging before it goes to hell... If heat wrapping, and running w/o Cats prolongs that significantly, that'll be a useful data point.

-Dan

Independent1

I hear what you are saying. The only reason I said what I did was because you said the fluid was recently changed and clear. If you cook the fluid the color usually gets darker and looks uglier. You said yours looked clear.

I am unable to logically understand how the pressure plate slipping would cause air in the hydraulic system. Maybe when you bled the system and thought you got all the air out there was still some left.

A couple of questions for you.

After this happens, do you have any problems shifting gears with the motor running?

Can you shift okay when the engine is not running?


If you put it in first gear and start the car does the car begin moving forward?

The reason I ask these questions, is that when the hydraulics in my 99 FRC failed I had these problems. Turned out to be a bad slave cylinder.

Good luck chasing this one down.

LF97C5Vette

Answers in Red:

I don't really believe it's a bad slave, it has done this on 3 slaves so far. So either i'm boiling the fluid, or air's getting in, or the clutch is causing this through some magic...

-Dan

Z06_BluByU

Yeah.. cars without problems have been running through my head as well.. But i've read a few posts from guys on the zo6forum.com and others here that have had the dealer install many clutch assys - including new hydraulic bits - only to have them fail quickly; (I think one guy had five dealer installed clutches/master&slaves in one year - all went bad in a matter of weeks).


my thoughts on this point to a very small threshold in which the clutch assembly (disc and pressure plate) is good or bad.. in combination with a small threshold of acceptable install procedure (i.e. not a lot of room for human error).. in other words a assembly could pass the parts QC (on the high end of the threshold) and have a little error on the install and be ok.. or be on the low end of the parts QC but have a very proficient install (exact procedure and specs followed) and be ok.. I think the problem comes from when marginal (but still pass QC) parts are combined with marginal install (again still up to install QC) that creates problems..

again.. just a working theory.. I have no teeth behind this except for speculation.. it jsut seems the adjustable pressure plate is the key component of the large majority of sticky clutch issues.. to get high clamp loads and low pedal effort is quite a trick.. I think this design needs to be setup and manufactured very precise which may be unrealistic for volume production and the wide array of uses these cars get..

what muddies the waters i think is sometimes there is issues with the master or slave.. especially from cars that sit alot.. that compounds the perception of the design.. (i.e. someone took a part a master assembly and found the rubber seals had tuned to mush).. however, I suspect that is the exception not the norm...


ok.. enough of my $.02

VetteDrmr

That says that something is either killing the slave or there's an air leak. I know we discussed it earlier, but have you checked the flywheel (as mounted on the engine) for runout? It only takes a couple of thousandths out to make a difference.

(Different car, I know, but I think the point is valid): I swapped the clutch out of my '94 Z28 and had the flywheel resurfaced at the same time. The highly skilled labor at the machine shop didn't get the flywheel square on the lathe and machined a tilt across the entire face of the flywheel: total runout from edge to edge (not center to edge) was 0.011". When I started the car up the vibration was there, and by 3000 rpm was buzzing hard enough to make me back off out of fear of breaking something. So it doesn't take much.

As I mentioned earlier, a friend of mine had the exact problem referred to by the TSB. IIRC, he replaced the flywheel, made sure everything was true and torqued properly, and hasn't had a problem since.

Something to think about.

HTH, and have a good one,
Mike

Old Rotor Head

Now I hear my issue coming to light. Changed to the LS7 clutch system complete about 20k ago. Nothing but issues. Somedays it's perfect then somedays I can't shift from gear to gear. Running Modul 600 fluid. I was changing it every other day with same results, now I just pump it 10 times between stop lights. Pedal has never stuck to floor? just hard shifting.

LF97C5Vette

Yeah - The clutch and flywheel aren't stock either. LS6 stuff w/ like 20k on them. It's been fine until the h/c/i swap, so unless the flywheel warped when the car was dyno tuned, i'm going to say it's fine.

Because 3 slaves have been through the car, I do agree with you on the point that there has to be something they all share causing the problem:

1) As other's have mentioned, the clutch causes it through some unknown, non comprehended magic, it creates this behavior, or...

2) The fluid causes it, whether through an air leak, or boiling.

I've done a ton of reading on this, and most of it is people advocating the ranger method, and drowning out all the other possible theories. Where Ranger has a valid method, and has helped a lot of people, it is clear that "Dirty Fluid" is not the root cause for myself, and likely many others... I'm glad to see other interesting theories cropping up...

-Dan

ajg1915

Lots of issues with C5's and clutches.

Personally, I advocate putting an after-market system in from Textralia, Spec, Ram, etc that will meet your needs or goals.

I don't like to see pieced together systems, where it's a flywheel from one source and a disc and pressure plate from another.

I run the textralia products in both mine and my bro's car (independent1) who already posted in this thread.

I always use fresh slaves and master cylinders when I swap or service the tranny. I use RPM's remote bleeders and Motul 600.

I have no clutch problems at all in my vette and don't expect any with my bro's car when we get it back together after it's over-haul.

Using a production clutch on a modified car is just asking for trouble in my opinion. The stock pieces are just not made to take what you're going to do it.

Buy a good clutch system and replace your hydraulics and put some heat wrap around the clutch line.

I don't know why you think you cats are killing your clutch, it's probably the heat coming off of your headers as your cats are much further back.

Throw on tunnel plate with coating or heat shield. There are lots of high powered vettes with six-speeds out there that work fine.

Using an inferior stock clutch is probably your problem.

LF97C5Vette

Well, I heat wrapped the exhaust, including around the collectors under the slave...

Made no difference... Clutch engagement goes to the floor after only 1 pull to 6500 and pedal doesn't come all the way up...

So far I think i've exhausted every option I can think of except going to an after market clutch.

I guess that's the next step...

If I buy an aftermarket clutch, and install it and STILL have the problem - I'm selling the car... It's just too damn irritating...

-Dan

miami993c297

Hi Dan,

One big help in my case was to wrap the line from the master to the slave and the use of reflecting material around the slave...

The combination of your new power found with the headers on your car are just creating a hot spot around the slave region.

Christian

nitrojunky

I found the adjustable pressure plate to be an interesting theory.

I have a guess on the details of what may be going on which can cause the symptoms listed (a few of the guys in this thread have seen it):

Something is boiling the fluid. Where I don't know...at this time I'm not sure because it seems to occur in F-Bods, too. I could see it being either off the headers or due to a slipping clutch.

I believe the following occurs:

Step on the gas, things heat up. Fluid boils, this causes a bubble.
While the pedal is at the top of its travel, the slave cylinder is 'free'* to put fluid in it (this is not the case when you step on the pedal because the 'bypass port' in the cutaway is now closed). But according to LS1tech, there is a very small oriface for the last inch or so of slave tube, so it takes some pressure to do this quickly. Furthermore (I could be wrong), but I believe there is a one way valve which demands a certain pressure before fluid can go this direction. Same going the other direction. The boiling fluid can easily make a couple hundred PSIG, so it displaces fluid into the reservoir quickly and allows the bubble to expand under 'low' pressure.

Step on the clutch pedal. Connection between slave fluid and reservoir is cut off, pressure in line rises dramatically, compressing the bubble. The pedal feels soft until you compress the bubble sufficiently. Engagement point has moved because bubble was compressible.

Every time you step on the gas with the pedal at the top of its travel, fluid boils, is displaced to the reservoir, and the bubble grows.

So the engagement point works its way down.

Then when you remove the heat source (get off the gas) things cool to below the boiling point in a few seconds. As soon as things get below the boiling point, the bubble's size goes to 'zero' as the fluid condenses, creating a vacuum. It does not remain as air would. Problem is, to move the fluid from the reservoir fast, a couple hundred PSIG is required. Vacuum is only 14 PSIG. So the fluid lost to the reservoir does not re-enter quickly and the pedal goes to the floor.

Also... this is kinda hard to explain, but if the fluid can't expand, the pressure of the bubble will rise as the fluid is boiling. So as long as the fluid is boiling, it will keep the pedal near the top of the travel because it will create tremendous pressure until the 'bypass port' is opened. Once opened, pressure will drop dramatically because the fluid can escape allowing the gas to expand like it wants to... so the boiling fluid can keep the pedal near the top, yet feel squishy. Then once the heat source is removed, it quickly (suddenly) forms a vacuum once you drop under its boiling point, dropping the pedal.

*this is how it self-adjusts. Same reason you can push in your brake slave cylinders by hand while doing a brake job even though they routinely put some serious force on your rotors. And yeah, the pic is from a 1940 merc, but I think the principles are similar

ajg1915

Personally I thing, it just a bad design. Clutch slave should be on the bell housing or better heat venting.

Without a remote bleeder and better hydraulic fluid you will constantly have the same problem.

No different then when you boil the hydraulic brake fluid do HPDE's. Once the fluid is contaminated it's boiling point becomes lowere and lower until there is just a failure.