mark kibort

ok, i have pedal, it got better on a drive around town to do some shopping. then, after the pedal was near as good as it has ever been, i did the High RPM run. AHHHHHHHH, the problem is back. high rpm, pedal goes near the floor before the shift. does it in neutral, but doesnt do anything if the pedal is depressed. (clutch engaged). I even found out that if i put slight pressure, the kind of pressure on the pedal that just moves it 1" or so to where it gets resistance and you hear that faint clutch switch click, i can rev the engine to 6k, shift and have perfect pedal as long as i dont let the clutch all the way out, to the top of the stop for the pedal.

so, it sounds like some vibration, normal or not normal is shaking the throwout bearing. could be the clutch pack that is now suspended and mecanically connected to the T/0 bearing when the pedal is pushed in. That vibration is now pushing the fork, and push rod in the slave back in so that the fluid runs backward to the through the open checkvalve. however slight pedal pressure doesnt allow this to happen to the pushrod, because fluid cannot go back to the reservior if the pedal is depressed sliglty. (1" or so) as the checkvalve is not sealed. so, is the check valve too big now? too easy for fluid to go back? is their a seal that might be bad there too?

I think its pointing to the next step, which is the clutch master cylinder replace. any thoughts now!!??????????????

mark kibort

HELP! what is next? change the master?????? or do i have a vibration problem from the clutch pack or flywheel . doesnt feel any different than it has for the last 3 years at 6000rpm. could the master cause this kind of problem?

jon928se

Just a thought - as I am away from WSM at the moment (in the office) I seem to recall that one or other of the clutch systems calls for 1 turn of preload on the pushrod adjuster on the pedal - Can't explain why but it may provide a solution given you description above?

RE bleeding - in my experience (and I've done it in some strange places like hotel car parks, side of the Autobahn in germany etc.) normally to get a succesful bleed easily you need to disconnect the pedal assister spring before bleeding to ensure that the MC and pedal comes to it's highest point, otherwise the piston in the MC covers the return port to the res.

mark kibort

interesting. But i wonder what changed???? its been running well for the 3 years ive had the chassis. but , certainly worth a try.

could there be an issue with the master that would cause this?

I think i misspoke earlier, when i was thinking of what what was happening. the 5000rpm that is causing the issue, is done with the clutch not engaged, so its the entire spinning clutch pack. the T/O is not really coupled with much force to the lever fork arm. Its amazing to think that some vibration could cause that lever to push on the slave push rod and cause this. I almost want to get under the car and feel the slave push rod at 5000rpm seems like there would be a lot of movement to cause the clutch pedal to fall to almost to the floor.

lastly, could this be an "air in the line" problem too?

trying the preload and see if that works.

mk

the flyin' scotsman

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mark kibort

Sure, I always like just replacing stuff, but you know me, i want to know why! why could it be the master, when it seems to be working well, and the fact that the push rod moving inward at high RPM shows that it is kind of doing what it is supposed to do. the root cause might be the push rod moving, due to some willd vibration, or if that check valve in the master is bigger or letting more fluid out faster than normal. I think that the pedal position might be looked at , as the preload that was suggested might work. (kind of a stretch ). But, also ,i wonder if there is still air in the liine, would that cause it.
going to do the pedal preload and one more reverse bleed and see if that changes anything

the flyin' scotsman

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mark kibort

Thanks Malcom, I understand. fortunately, this problem happened the day after the last race of the year. and i drove the car home from the track too, with no issues. so, i do have some time, but have already wasted over 8 hours on the problem . time to cut the hole and put in the master? after all, i have the part in my racing bag!! by the way, is there any difference between masters from the old years to the newer years (i.e. S4) ? The one i have is either for a S4 or 84, or maybe they are both the same.

the flyin' scotsman

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mark kibort

I think this is the next move. master going in next! uggg, time for the hatch cut (hack as GB would say)
and yes, im using an Axe to do it!

GregBBRD

I told you what was wrong....and all you wanted to do is be defensive and argue about it, telling me that I needed to go back and figure out how the clutch in a 928 works! I'm the guy that just spent months completely re-engineering a complete dual disc carbon carbon clutch for these things, after trying, for years, to 'solve" the inadequacies of the stock 928 clutches for high torque/horsepower use.

You look at three clutches, in your entire life....and you are the "expert".

The fingers on the pressure plate are uneven and that forces the T/O bearing and thus the clutch slave back at high rpms. You need to "pump" the pedal to "return" the clutch slave to the operational position....just like when you need to "return" the brake caliper pistons after installing a new set of pads. The "vibration" you feel is this "slightly" out of balance condition.

Duh.

"See Spot run."

mark kibort

Ok, you bring up things that are unrelated. yes, the clutch is deficient, and this happens at the much higher hp ranges, plus they are fickel with the H adjusters. BUT, we are talking about my clutch and what is out of balance. again, the H adjusters are all at 1mm and have not changed since the clutch was pinned 3 race seasons ago. Ive done this to scots..... also perfect ........ so, you are the "expert" so what is it? Yeah, ive worked on "3 clutches" and Im the "expert". no, im not the expert, but i did straighten out your vision of how the thing worked when i was trying to figure out how the INT plate worked and how we could salvage it. remember how you said the "litttle H adjusters get slammed by the retracting INT plate" remember how you found out that was not true?? Also, do you remember your private emails thanking me for my descrition of how the the INT plate works and really what forces were acting on the H's.

Look, im not here for an ego battle. im hear to figure it out. if you really get the INT plate function , (not your redesigned brilliant high HP clutch swap out) , then you can help me figure this one out . (if you really care about helping, and not just blowing your horn to prove who is smarter)

So, the INT H adjusters have not moved, they are set at 1mm each. the clutch works perfectly until 6000rpm, but i have to tell you , after the accident where the Holbert car went into the wall, the engine always had a little vibration. think about all that mass hanging off the edge of the crank nose. all we need is a little bit of run out and there coudl be a vibration. (i thinik ill put a dial indicator on the flywheel and see if that is the issue) However, it has not gotten any worse for 3-4 years of NO issues.

My question to you is, can this be a master cylinder issue where the fluild is allowed to reverse flow, as it should , but its doing it too easily do to a seal problem or the checkvalve being larger somehow.

So, put the ego aside. the INT pilate pinning is a non-issue. they are set at 1mm and the weight of a small roll piin in the 3 locations is not an issue.

So, any suggestions? just change out the master cyl, or check for flywheel run out? could also be the torque tube , as the vibration at 6000rpm feels a little better with the clutch pedal in. this eleminates the clutch discs, short saft and the entire drive line to the transmision. just a thouight.

Mk

Charley B

Foul!!!!

Bringing up private e-mails on a forum is like asking a man if he still beats his wife.

GregBBRD

Mark:

Seriously...you think I'm here helping people for my ego?

I obviously can't help you with this. Have fun with your toy.

mark kibort

I dont know, are you? some of the thins you say, seem to be ego driven. dont just ask me, ask the others here! if you want to help, help! I think you can help, but you are more intersted in proving something that works, (pinning the H's) is the cause of my problem. agian, i dont think its the H adjusters, because they are all set at the 1mm gap. So, giving me the benefit of the doubt, what else could it be? if the flywheel shows some runout from the accident, then what? The fact that it all of the sudden started to be a problem, is the thing that is troublesome.

I dont have a lot of knowledge about the other components, but you seem to do, so i wonder what your thoughs are on the master cylinder being a problem.