Boiling Clutch Fluid? Cats at fault?
 

So, I've been battling this sticky clutch pedal problem for some time. The car has a LS6 clutch with maybe 20k miles on it, and a Brand New (2 weeks old) master and slave cylinder, with Motul 600 Fluid (500F+ Boiling Point.)

After swapping the master and slave the sticky pedal problem was gone, for about a week of daily driving, and the occasional jaunt up the gears... I don't drag race or even drive it hard all the time. But now, if i wrap out a gear, the pedal will stick on the floor.

Fortunately for me, I installed a remote bleeder during the slave swap, and can bleed the fluid. I decided to check out the fluid immediately after experiencing a sticky pedal. What did i find?

Air in the fluid. :willy: Perfectly clean fluid with lots of tiny air bubbles coming out of the bleeder... And I mean lots of them... So I bled the fluid until no more tiny bubbles were coming out, then i took the car out again. Guess what...

Clutch worked fine. I could wrap out 1-2-3 w/o any problems... so i gave it a good flogging a few times, and after 5 minutes of ups and downs wrapping it out, the pedal started sticking to the floor again...

I'm fairly certain I'm boiling my fluid...

I have DTE Long tube Headers, High Flow Cats, and X-Pipe. The Cats sit right below the Slave Cylinder under the car, and I'm told can reach temperatures in excess of 1000F pretty easily...

http://images.vetteweb.com/features/...rside_View.jpg

Does it seem likely that my fluid is boiling? The symptoms seem to indicate so, because when the pedal sticks the clutch is fully engaged; which suggests a loss of hydraulic pressure.

My friend suggested trying it w/o cats... I'm very curious to try this but wanted to ask CF:

Does anybody here have the Sticky Clutch problem who're not running Cats of any kind?

Thanks,
Dan

How often do you change your clutch fluid? and what are you putting back in?

Well, when I installed my New Slave, Master, and Remote Bleeder a few weeks ago, they came primed with something, but I ran an entire bottle of Motul 600 through the system, and that fluid has less than 500 miles on it... No drag racing, or anything, just the occasional 1-2-3 pull, maybe once every 3rd day... Trust me when I say the fluid is in pristine condition.

Last night I flushed about 5 Master cylinders full of fluid through the system, Motul 600 again, and the Sticky Clutch pedal was completely gone, for at least 3 pulls through the gears. But then it went to hell again...

I'm going on the theory that clutch fluid is boiling here, and am curious if anyone has had the Sticky Pedal while NOT running cats?

-Dan

Would it be possible to put some kind of metal heat shield between the master and the exhaust? I'm thinking of something clamped to the exhaust tube(s).

HTH, and have a good one,
Mike

I was going to put some reflective heat shield on the areas above the Cats to try and keep temps down some... and thought if i run w/o cats (slip on a section of straight pipe) i could heat wrap that pipe too, and really drop the temps. I don't really want to wrap the cats... sounds like a bad idea...

I called GM and asked about their latest TSB... the Rep told me that there's one where the pedal doesn't return after being depressed during High RPM shifts. And their diagnoses was the Pressure plate wasn't torqued evenly and wobbles a little, and that wobble over time causes vibrations and wear in the slave cylinder which leads to poor sealing and under stressful conditions air can enter the system.

I think that sounds like BS because I ran with this clutch/slave setup for months and months w/o any problems, and It never started acting up until after the H/C/I swap and a Tune. And now, even with new Slave it goes bad in only a few days... I can't imagine a Wobble (that i can't feel) deteriorating the slave in only a couple days..

If this is a heat related problem, I'm afraid swapping to an aftermarket clutch won't fix my issue, and I don't want to go through all the trouble if it's not a sure fire fix... heh


-Dan

try sliding some "cool socks" or thrermo sleaves up your clutch line. I used to have problems launching after long burnouts do to the headers heating up the line.

Now the problem becomes much clearer. You need a stronger clutch.

Stock one will NOT hold a higher hp h/c car. Forget about the hydraulics and just install a new clutch ass'y that will hold the power.

Even if you think you can't detect it...your stock one IS slipping at the higher rpms/higher hp, and nothing short of a stronger aftermarket clutch will solve your problem.


:cheers:

I agree with you that your problem may not be related to the TSB, but it is valid; a friend of mine with a '97 MN6 was having this problem and determined that the flywheel was "warped", due to improper torquing.

The heat shielding I was thinking of was not a wrap, but instead a thin piece of steel (Home Depot flashing?) mounted between the headers and the master/fluid line.

Have a good one,
Mike

I am having the same issues as you but I do track my car so I see it happening at high rpm shifts especially after the whole car has heated up after a few laps. I run long tubes and no cats with a h/c package.

I dont think its the cats because the long tubes are more in the area of the clutch hydraulics. I have been thinking of trying to install a heat shield between the LTs and the master, but I think it would only delay the problem since the heat would eventually come through.

It might work for you since you dont track the vehicle. However for me, after 15 mins of a 20 min lapping session, I think the heat would get in there no matter what I do. Time and time again people that had the sticky clutch and went to an after market clutch have said that it has cured the sticky clutch problem.

I think my ultimate solution will be to go to the LS7 setup while adding insulation to the hydraulic lines and possibly a heat shield. I am surprised that nobody makes a heat shield for all of us that have LTs.

I have also looked at the McLeod Master Cylinder since it is an actual metal housing instead of plastic that should resist heat a little better. Its also adjustable, so if you get it, make sure you arent going to a clutch that isnt compatible with and adjustable master (ie Tex)

When I installed my new Master and Slave cylinder i wrapped every inch of hydraulic line (including the remote bleeder) with reflective, insulated heat shield.

It's not a Stock clutch, it's a '97 Coupe with a LS6 Clutch that has 20k miles on it. I would've thought the LS6 Clutch could hold 385-410 whp... My tuner says my torque curve shows none of the classic signs of a slipping clutch... (And every run we made we had to pump the pedal between runs)


I can clearly see air getting into the lines. It's fact, no arguing that air is getting into my hydraulics. How will an after market clutch prevent air from entering the lines?

Thanks for the input guys, this is a genuinely frustrating problem. My tuner knows a couple other guys w/ similar setups who aren't having this problem...

-Dan

Interesting idea, but can you explain this:

If my slipping clutch is causing the problem, why can I push the clutch pedal in with the car in Neutral, and Rev the engine a couple times, and the pedal doesn't come up... :willy:

-Dan

I think the stock pressure plate isnt able to withstand the added power and thus starts to flex under load which then flexes the slave not allowing it to work right which allows air to enter system somewhere. /runonsentence

If the clutch pedal is depressed while revving the engine, the pressure plate wouldn't be under load right? So that wouldn't explain why reving with the clutch in lets air in?

-Dan

I dont know if the pressure plate is deforming or not thats just another explanation as to the sticky pedal. Everyone seems to have a different explanation and the only thing we can agree on is the stock C5 clutch stinks and should be replaced with one of the aftermarket/LS7 flavor.

I'm pretty sure the LS7 clutch will get sticky pedal syndrome, i'm fairly certain I've read about it... though i'd have to search for the posts again...


-Dan

Get rid of the LS6 pressure plate. It has an effortless pedal for a reason.
I wouldn't use a LS6 or LS7 clutch set-up on anything that is modded, raced, or run past 6,000 RPM.

From what Ive found from the research that Ive done, the LS7 setup doesnt like repeated standing starts (ie drag racing) but for track use, like HPDEs, it holds up fine as long as you do the proper maintenance from the remote bleeder. Ive talked to several people both on here and at the track that have the LS7 setup and do not have the sticky pedal syndrome. It is a risk since its a GM clutch, but for the price that I was quoted for, its hard to pass up.

I have been researching clutches and this subject for about 3 months now and thats just the conclusion Ive come to. The main recommendation that I get is from the shop thats installing it in my car, and they have yet to steer me wrong as they work on cars that are much more extreme then mine that go on the street, strip and track.

I think its the self adjusting pressure plate in the stock OEM setup (LS1, LS2,LS3,LS6 and LS7)... this is the only explanation why aftermarket setups dont have a problem.. (no fancy light pedal effort adjustable pressure plate - which also has high clamp loads)..

I've read a few folks both on the C6 and C5 forums who have had problems, kept the stock hydraulic setup with aftermarket pressure plate and all is good..

my working theory is that under high RPM the stock pressure plate adjuster backs off (After a few high rpm shifts - centrifugal force) and causes a weak pedal (dirty fluid exacerbates the problems) which can cause it to be firm, come half up or stick to the floor. this so far also seems to explain why everything returns to normal after a pedal pump or two (and the adjusters reposition the stock pressure plate correctly).

This makes the most sense to me out of any theory I have ever read. :thumbs:

only wish i had a exploded view, detailed pix of the inside or a old bad OEM pressure plate to take apart and to see the workings of the adjusted assembly to give this theory more teeth..