nitrojunky

thought about it some and came up with a theory. not sure if it's been explained this way or not

nitrojunky

method to test theory:

(do not try at home or on public roads, yadda, yadda)

know volume of one clutch-stroke. if it's large enough to be -very- noticeable on reservoir...

a) mark reservoir level
b) do WOT run thru a few gears, enough to make the problem very, very noticable
c) at last gear, put car in neutral (still with mushy clutch)
d) hopefully, pedal is super mushy and goes to floor after coasting
e) coast to stop, measure fluid level

if it's high, then I'm pretty sure it's a clear indication that boiling fluid is the culprit. If there was no boilage, then there should be no change in fluid level.

This won't work unless one pedal stroke worth of fluid is very noticeable because the issue (at least in the case of my car) is anywhere from 1/4 pedal stroke to 3/4 pedal strokes' worth, and the car will likely not be very level at either the start or the finish.

LF97C5Vette

I have installed a remote bleeder. I just wrap it out - then pull off and pump out the fluid. I can see lots of tiny little bubbles in the fluid indicating I've boiled the fluid, there's no question my fluid is boiling. At least not for me.

Yours is an interesting experiment for someone with some time.

-Dan

gpracer1

If you were really boiling anything, when it cooled down, you would recondense back to fluid.


There is the pressure plate housing, and the pressure plate friction plate. In between those two there is a daiphagm spring. Now there has to be a pivot point for the plate to move back and forth on. I am assuming they are a few pins. I have a feeling that at elevated HP and rpms, the pivot point is binding or sticking and coupled with high rpm centrifical forces holding the fingers in, the fingers are not returning all the way which will reduce the pressure back on the pedal. Therefore the pedal does not return all the way.
Ill bet if someone disected a used "sticky" clutch, they might find some wear on the internal parts of the pressure plate.

nitrojunky

this is central to my hypothesis/test. when it recondenses, the pedal will go to the floor, and the reservoir level will be higher... until you pump the pedal a couple times.

Not saying yours is wrong, but so far I can now explain every symptom I've experienced in both my C5's with boiling fluid.


The prob I have with the cenripetal forces is... this doesn't occur when I do a 6500 rpm rev, only when I put the car under power, then shift. Also, it will continue for three gear shifts afterward, and at low rpm, i.e. if I go WOT first, second, and third, then let out, subsequent shifts to fourth, fifth, and sixth will occur with pronounced 'sticky pedal'. This means RPM isn't so much a factor, and if something was binding, it continued to bind for at least three shifts (and at low rpm) after the issue.

K RIPPER

Heres an idea, someone w/the clutch prob.remove the dust covers (the ones behind the oil filter & starter,starter side you must unbolt starter slide back starter to remove that side you don't have to remove starter) run car w/covers removed there should bee a reduction in temp. in bellhousing, if you really want to get creative you could temp mount a couple of whisper fans to blow air through both sides (fans can be scavenged from old computers they all have them & most are 12volt or buy from radio shack($20ea.) may lessen prob. or recovery time may get better so the prob. is manageable till perm. solution is found

Warp Factor

Yup nitrojunky, you nailed it!

In my case, I emptied my reservoir, then filled it from a syringe that had the level marked on it.

Went out and "stuck" the pedal with some sloppy power shifts, then wedged a stick between it and the drivers seat to hold the port to the master closed so fluid couldn't get sucked back out of the reservoir as gases re-condensed. Bumped the gear shift into neutral and stopped.

Put the fluid back in the syringe, it was higher than before. Not sure exactly how much (wasn't a graduated syringe), probably at least 2 cc.

Car was pre-heated, so it wasn't due to expansion from engine compartment heat.

ZeeOSix

If it was that, wouldn't the pedal pop back up at some point as the RPM decreased and the centripical forces reduced? Does the pedal just pop back to normal as the engine RPM decrease, or does the driver have to reach down and pop the pedal back up after the engine RPM is decreased?

Old Rotor Head

I read every one of these theories with great interest. I've got a bone stock '99, put 100k on it before I changed the original clutch and never had a problem, never changed fluid once. Had others install the LS7 kit complete and had nothing but a PIA since. Running Modul 600, don't race, daily driver do hit 6k RPM every so often but then I can't shift into gears up or down. Pedal has never stuck to the floor, I can pump it 10 or so times and it's ok. Other day's it's smooth as silk?

I believe GM knows the problem and probably the fix but with LS cars out there from 1997 through 2008 it's cheaper to keep your head in the sand.

K RIPPER

Just got my chassis service manual back from friend who's putting all c5 running gear in a mid engine corvair ,I went to the section on clutches and under that troubleshooting section they mention adjusting the pressure plate, they give a procedure but don't explain exactly what the adjustment does ,I would guess that you are adjusting the clamping force, I will find out but in the meantime can anybody shed some light on this??? With all the discussion on sticky / spongy clutch no one has mentioned PP adjustment PS it can be done in car or on bench

ZeeOSix

I remember having some discussion about this before ... nobody could determine exactly what the adjustement was for. Not sure if it's the clamping force, as the would techically be determined by the clamping springs on the pressure plate I would think.

http://forums.corvetteforum.com/show...ghlight=clutch

K RIPPER

I was just looking at the stock pp that I replaced a while ago it looks like there are stamped into the pp cover a series of wedged shaped openings behind which is the adjusting ring (lands?or fingers?)and when you turn the adjustment ring the wedge openings force the ring down,either maximizing spring press..... or setting spring height to have the correct clearance(on .throwout bearing) and at specified height having the recommended spring press.the throwout brg. is self adjusting, automatically adjusting out a specific distance if spring height is wrong to brg will contact pp all the time but should only contact when clutch is engaged constant contact it will survive for some time but when in direct,constant contact w/ overheated pp heat transfer can take place....if adj. ring sets spring height(therefore setting throwout bearing clearance)...if both are wrong.. slipping clutch and a constant running bearing on a burning up clutch this kinda makes sense. the adj. ring is there for some reason anybody know for sure??

ZeeOSix

What do you guys think of this info from GM? Seem like there is more to it then this, or maybe this is one of the issues with the clutch along with some others that GM hasn't addressed. The bulliten only says "2005 Corvette" ... humm.

http://www.corvetteactioncenter.com/kb/questions/481/

http://www.corvetteactioncenter.com/kb/questions/664/

Warp Factor

Ha, that's funny!
In the second service bulletin, Chevrolet is finally acknowledging a problem with boiling clutch fluid.

They make some good points about handling brake fluid though. Some people aren't careful about moisture content of the fluid, and then wonder why they get no improvement when changing or flushing.

Brake fluid absorbs moisture from the air, and the boiling point goes way down with moisture content. It's best if it comes from a fresh, never-opened container. Once that seal on the top of the container is removed, the fluid goes downhill.
Minimize the time that the cap is off the clutch reservoir. Try to choose a day when the humidity is low to remove the cap and service the fluid.