jtl12419

iTrader: (13)

Help me figure out whats happening on road-race track (enduro type environment):

I have a high HP (>500 engine HP) LSx in a 93 RX7-FD, with fidanza iron flywheel and stock Z06 clutch disc/plate, running to T56 6-speed tranny that's been beefed up. Tilton style separate master cylinder to the factory stock slave throwout bearing.

When I run hot, really aggressive shifting using 4-5th gears, clutch seems to engage when my foot is nowhere near the pedal. When I'm really into the horsepower on the straights, engine revs but disconnects from the tranny (My foot is OFF the clutch). I smell clutch material, and clutch pedal gets very hard, but does not go to the floor, I cannot shift any gears. When this happens, I put the car in neutral and coast/limp until ?cools off?, then I'm back to normal for another lap, then it happens again.

I sense that its "temperature" related, because the more aggressively I drive on the track, the more this happens. No problems driving on the street, clutch does not slip normally at all.

This happens when I am NOT pushing on the clutch pedal. I do not ride the clutch.

Initially, I thought it was the fluid boiling, but clutch pedal never goes to the floor. I tried Bleeding the clutch several times with new fluid and rerouted the line so its nowhere near the headers, and still its happening.

Need ideas.

85MikeTPI

iTrader: (9)

Almost sounds like the clutch might be dragging, and heating up the FW/disc to the point that they are engaging. Check for high RPM clutch drag while cool to see if you get any creeping. Do you have a shim behind your slave ?

(Boiling the fluid would have the opposite affect, causing you to lose pedal and not shift gears with the pedal down)

jtl12419

iTrader: (13)

How do I check for high RPM clutch drag when cool?

I did notice that it happened every time I ramped to 6000+ RPM in 5th gear with full throttle, less so if I ran RPM's up slow.

If the clutch is dragging at high RPM, what's happening and how to fix? Why would my C-pedal get rock hard?

This was not a slow and gradual event, one second it was fine, the next it was not-- but always came when I was pushing it-- like trying to catch another car.


TIA

SS101

iTrader: (2)

to check for drag: find a level spot of ground, so level that the car will not roll in neutral. put the trans in first, depress the clutch all the way, and rev the motor up to just below redline. if the car jerks forward, then your clutch is dragging.

SPEC-01

iTrader: (2)

When you have checked the fluid, after this occurs, did you notice that it was dark or cloudy? It honestly sounds like the fluid is boiling and thus aerating which leads to fluid displacement. This in turn could cause the TOB to extend and to apply pressure to the diaphragm (partially releasing the clutch) which would allow for slippage. You can certainly try to see if the clutch is dragging as described above. But, I would also suggest using a higher BP hydraulic fluid (I am a fan of RBF 600 from Motul), as well as wrapping the lines with a good heat wrap and insuring that they are routed properly. Let us know what you find and we can go from their with more suggestions. Thanks!

jtl12419

iTrader: (13)

What about the hard pedal when this happens?

We were in a hurry to get tracktime, and flushed with Castrol SRF and relocated/insulated the lines on Friday added air ducting, ran Ok at 6-8/10th the rest of Fri and Sat, but I avoided full throttle attacks, and kept it in 5th gear AMAP.

Sun, I push it again with active corner downshifting, and again the problem returns within 5 laps.

In our rush, there may possibly be residual air in the hydraulics. (It took us a long time to get the air out on Friday- its a PITA to do in the pits.) In retrospect, one thing we did not do is bleed at the slave cylinder.

Would heat expanding air in the slave have pushed the TOB making it a hard pedal? Sounds counter intuitive-- I would think air in the hydraulics would make the clutch pedal go limp.

I just want to ascertain this is not a clutch/flywheel mated to engine HP hardware issue. If so I would put in a new clutch before my next event.

Thanks for the replies. I do appreciate it.

josh18_2k

i'm having the same issue.
'00 F-Body LS1 w/ 315whp, OEM slave, OEM Z06 clutch, Fidanza flywheel.

at the drag strip my pedal would get hard at the end of 4th gear. Its been doing this since I built the car. Only time it ever happened was 4th at the drag strip, so I didnt ever address it.

i dailied/autocrossed the car for 20k miles with no issues.

over the winter i put in a new trans and bled the clutch with Motul 600.
did two autcrosses, no problems.

last friday i went back to the drag strip and the pedal got hard in 3rd. shifted to 4th, and the clutch started slipping at 5500rpm.

autocross 2 days later: and the pedal gets hard, then starts slipping in 2nd gear at ~30 second mark.
I launched in 2nd from then on, and it didnt slip, but the pedal was hard at the end of each run.

SPEC-01

iTrader: (2)

Due to the fact that the pedal is getting hard (which is not typical of boiling the fluid) it sounds like both of you may be having issues of fluid bypass. This can occur if the internal seals of the slave/master are allowing fluid to pass through causing the plunger that moves the fluid to be unable function. The plunger would effectively be seeing pressure on both sides and would thus only be able to compresss as much as the bypassed fluid would allow. Do this...check the fluid again, bleed the system thuroughly again, and see if the issue returns. If it does then I think it is pretty safe to assume that you need a new slave or master. The down side is that there won't be any real way to tell which is the culprit unless there is evidence of a leak. I hope this helps. Let me know if you have any further questions. Thanks!

josh18_2k

would that explain the clutch disengaging on its own?

SPEC-01

iTrader: (2)

If the slave or master were bleeding by then it could cause pressure to build up and ultimately lead the bearing to begin to compress the diaphragm. This normally occurs over the period of a few shifts as fluid seaps past the seals with every pedal depression. I have seen it first hand!