clutch pedal won't fully come back after hard launches

[tasinb5s4]

I'm taking car for drag strip ones a month or so. ko4 e85 11.8 @125 ,11.7 @122
running Ringer Racing stage 4 clutch ,USP slave kit -fidanza flywheel
after burn out or hard launch clutch pedal will not comeback alway back for few second then after will pop right back in ,or during pass between shift it will do same thing then clutch will slip bad , it feels like you push on the clutch just bit

NO problems with clutch
no problem with master or slave cyl .
multiple clutch & hydraulic parts where tryed
fun part about it its intermittent .

some how brake fluid reservoir gets pressurize just enough to keep pedal just bit down keeping clutch from full engagement .( thats my guess)


plan is to run separate reservoir for clutch fluid ,
ANY INPUT? anyone experience this type of problem

[LightningLou]

I had the same issue and am also running the same clutch. I switched to Motul RBF600 and bled the brakes and clutch line thoroughly and haven't noticed the clutch pedal sticking anymore after hard launches. Btw does your clutch make noise at idle unless you press the clutch pedal in?

[killerkali]

I have the same problem as well. Also occurs after shifting at high rpm, almost seems like boost is making its way into the system

[Lanorg]

does anyone know what temps are being seen by the fluid? perhaps that plays a significant role?

[LightningLou]

does anyone know what temps are being seen by the fluid? perhaps that plays a significant role?

That's why I switched to the Motul RBF for the high boiling point. To me, it seemed like the fluid was boiling and causing the slave to stay extended from the pressure.

What brake fluids are you guys using that have this issue??

[tasinb5s4]

i don't know if different fluid will make change , the other morning it was pretty cold it did on me .
im gonna try to separate clutch line from brake reservoir . I'm more then sure that has something to do with EDL, i tried with abs plug off to still having that issue

[tasinb5s4]

I had the same issue and am also running the same clutch. I switched to Motul RBF600 and bled the brakes and clutch line thoroughly and haven't noticed the clutch pedal sticking anymore after hard launches. Btw does your clutch make noise at idle unless you press the clutch pedal in?

no noises clutch woks perfect

[rpallen85]

i don't know if different fluid will make change , the other morning it was pretty cold it did on me .
im gonna try to separate clutch line from brake reservoir . I'm more then sure that has something to do with EDL, i tried with abs plug off to still having that issue

It's worth a shot. Brake fluid is hygroscopic. It absorbs water over time. That's why brake fluids list a wet & a dry boiling point. That water / heat changes the viscosity, after which it can seep past seals. Have you ever bled your brakes & clutch? You may want to bleed your brakes & slave / master cylinder with all new fluid.

If that doesn't work I would move down the line to replacement of parts.

[julex]

couple of things to consider:

1) Possible problem with diaphragm. When heated up it might change shape and not exert enough push to overcome slave spring + pedal resistance. IF you don't run pedal stop on high engagement point clutch (like this one I think is), then you over extend the diaphragm which combined with it changing shape (due to heat) and less force might cause what you see, diaphragm gets close to the point where it want to "pop" into the reverse conical shape (but has no room for it) and thus why there is very little incentive for it to get back into original shape and thus it doesn't push on TOB much.
2) Possible fluid over heating but lets think about it for a second. That can't possibly be overheating due to friction material temperature since slave, the closest part of clutch hydraulic system sitting to friction surfaces, is not in contact with high temp parts, it sits comfortable in the back, 90% of it outside too and I don't see hoe rapid heat transfer might happen here. There is one other way for fluid to heat up and that's outside of bell housing. Downpipes are darn close to slave/lines so maybe heat wrapping/sleeving is the way to go.

I bet on #1, install pedal stop and see if that eliminates the problem.

[tasinb5s4]

i was using vw Audi brake fluid
With boiling point deam close to most race brake fluids ,
I'm tech everything on the car top notch
Fluids getting serviced yearly

Plan for weekends
Picking up motul brake fluid
Installing separate clutch reservoir
Heat wrapping line and slave cyl !

[tasinb5s4]

Where you guys usally mount a pedal stop ?

[julex]

i was using vw Audi brake fluid
With boiling point deam close to most race brake fluids ,
I'm tech everything on the car top notch
Fluids getting serviced yearly

Plan for weekends
Picking up motul brake fluid
Installing separate clutch reservoir
Heat wrapping line and slave cyl !

I don't think boiling is your problem. Install pedal stop so that you don't hyperextend diaphragm every time you press that pedal to the floor.

[james 408]

I wonder if it's just as simple as a bit of air being in there? try rebleeding? I'm with Julex's guesses as well, and I think Lou (and maybe a couple others) are saying the same thing. I know air naturally works its way out of the system sometimes so it might solve itself by just driving it.

I personally don't like pedal stops -- when you actually get a leak, you can sometimes get one or two launches out of the system by burying the pedal. This is a minor point though.

[tasinb5s4]

I bleed it few times ,
What I notice when pedal stocks lil low you open reservoir cap , pedal pops back in

[rpallen85]

How much fluid did you bleed? May still have air.

[tasinb5s4]

Don't think that's air problem ,
Igot mashine for brake/ clutch bleeding ,

[LightningLou]

What method are you using for bleeding? I would invest in a Motive bleeder that pressurizes air through the brake fluid reservoir and refills as necessary. Works like a charm and guarantees all air is pushed out of system. Makes bleeding brakes a breeze

[tasinb5s4]

Using Mac brake fluid mashine , we using that mashine in all vw/ jaguar cars , it just pushes fluid true the system , you can set diffrent pressures ,

[tasinb5s4]

Today went junk yard , grab clutch reservoir from Hyundai Accent , installed on my car ,
Also got some Motul RBF 600 from local bike shop ,
Bleed the system everything works like a charm now , also made a pedal stop from ekhaust hanger :) , drove it all day with no problems
Next weekand race track will see how it's going to perform !
Thank for healp

[mkemk3]

I had the same issue and am also running the same clutch. I switched to Motul RBF600 and bled the brakes and clutch line thoroughly and haven't noticed the clutch pedal sticking anymore after hard launches. Btw does your clutch make noise at idle unless you press the clutch pedal in?

I have the same flywheel and there is a bit of chatter at idle. The second you press the clutch it goes away.