mark kibort

sounds logical. but what about the fact that the slave doesnt have much of a shaft length extended when i assemble it. all slaves ive ever removed ALL have to have the shaft pressed back into the assembly to put the slave on the bell housing and bolt it down. mine is way to easy to assemble. when i have the slave in hand, and push the actuator shaft back into the slave, it doesnt move very far whille pushing the fluid back in the line to the master. usually, there is a lot of throw here. could there be a spring in the slave thats bad? what is the force that pushes the shaft so much farther in other cars? again, it wasnt like this when on the holbert car either. could air be the reason for that as well.

IM going to bled it and see what comes up.

thanks

Mark

GregBBRD

I also provide these clutch hoses with a heat shield already attached.

dprantl

A properly functioning slave cylinder should push the shaft all the way out by itself. It should require some force to push the shaft in. There is a spring in the slave cylinder that does this, and it is possible that the spring in your cylinder has somehow become cocked or is damaged.

Dan
'91 928GT S/C 475hp/460lb.ft

GregBBRD

I wondered how long it was going to take for someone to figure this out!

If the intermediate plate wears or moves slightly (or wasn't ever perfect to start with), in one of the three "pinned" spots, the clutch surface that the rear disc sits on will not be "flat" in relationship to the pressure plate. When the pressure plate is released, the fingers will not sit flat and they will push the entire T/O arm rearward. The forces will "grow" as the rpms get higher, pushing "rearward" harder. You need to "pump the pedal" to move the hydraulic slave close enough to function....just like when you "return" the brake pistons to install new pads.

It is certainly possible that one of your "welds" has let go and the intermediate plate is sitting "off level".

Porsche isn't stupid....there's a reason they didn't pin these things or make them with a "bolt" that "locks" them down.

mark kibort

just bled the system. put the pressure bleeder on and also cracked the valve. it dribbled out. then pushed the pedal down slowly with my hand . up and down very slowly.. did it again until the fluid came out nice and blue , it was kind of gamey at the start. (dirty). so, just closing the valve, the pedal is immediateluy at full height with pressure on the system as it is depressed. thats good, i guess, so it feels better now too, but havent driven it yet. will later today if it drys out. I wonder if that was it. air in the line?? and, i have no idea if i did the bleed correct, but pressure bleed and open the valve with fluid moving out, cant be all bad, right?
thanks for the input guys. if this works, its the air in the line thing. if it doesnt, maybe start with a new slave and go from there.

mark kibort

so , i get it. if the spring is soft, then it wont push the shaft out, but it wont effect much as long as there is pressure and some spring pressure . if the spring was good, it would push the shaft out and it would pull fluid with it. then, to get it back, it takes force to get it in the bell housing.

oh, wait a min, maybe you are on to somethig. the spring pressure is there to keep the pressure on the lever fork arm. with out it, vibration can cause the fluid to pushed back, especially if the spring pressure is not helping here. something to think about too!

mark kibort

If you read what you said, you might want to think about your view of the mechanism.

first off, the H tabs are stilll in place with a fixed 1mm gap, proving that what i did works and is a good modification. the only time it WONT be a good thing, is when the discs get worn to the point where the H tabs wont allow forward motion to make proper contact with the flywheel. They are self adjusting to that point and that point alone! porsche was not stupid, but they made a part that could get old and those H adjusters friction can get weak and during racing, and racing alone, they can be a problem, as I have and scot's seen.

So, lets just say the H pads were off, upon clutch engagement, the intermedate plate would retract toward the pressure plate, and if one H was off, its concievable that the int plate could be canted. that might cause some undue vibration. the pressure plate is being deflected by the lever action of the fork suspended by the upper attachment pointon the bell housing and the slave with its shaft. the intermediate plate is now floating and connected mechanically to the clutch pack via the H tabs, so if there is vibration, it could be transfered to the clutch pack and maybe to the pressure pate which could send vibration to the slave shaft and push fluid back.

anyway, there is such a small distance that the H adusters can be off that that is a stretch., but since the H's are all in set formation , at 1mm , which is the stock setting, AND if they were more than 1mm, there would be some rearward contact that would make shifting hard, which it is not.

So, the H's are ajusted. 4 racing years later, and a ton of street miles, they are holding firm, and why wouldnt they . they are pinned with roll pins and the forces are not that much acting on them. just enough grip, to keep them from ever moving again due to any vibration the intermediate plate would have at 6000rpm only resting on the H adjusters. an order of magnatude more force that the springs apply to the H adjusters when you push the clutch pedal in.

how does the intermediate plate put pressure rear ward on the T/O bearing assembly if it was out of balance . just curious. trying to think about what the T/0 bearing is doing when you push the pedal in.
when the clutch is pushed in, the vibration of the assembly is supported and connected to the lever arm and T/O bearing, sans the discs, shortshaft and drive line. (all now free and discoinnected mechanically) any vibration could be passed to the t/o bearing, and put some pressure on the slave shaft.

GregBBRD

Yeah, that's why I didn't want to even go here and waited for someone else to mention it.

Not really in the mood to argue with you about this. You asked what could be wrong, not me.

I'm pretty sure I don't need to think about how the mechanism works, BTW.

UncleMaz

I was amazed how thrashed jjbyron's clutch disc (on pressure plate side) and PP were thrashed before we replaced them. In contrast, the flywheel and IP were tip top (as well as the flywheel side disc). Based on what I saw and what GB continually says, I wouldn't pin the intermediate plate adjusters.

mark kibort

one has NOTHING to do wiith the other. the reason you get one to burn out more than the other is just a factor of how the car is driven and shifted. things do wear out. ive pulled apart a bunch of clutches where the INT plate is trashed more on one siide. the pressure plate is trashed, and flywheel is fine.

pinning has nothing do to do with this. its lke saying , keeping the clutch in perfect adustment will cause issues. ......................... its just silly.
I think YOU do have to understand how the clutch is working, with respect with the iNT plate. all the H's do , is limit the rear ward travel of the Int plate, when you push the clutch in. thats it. the the force of which this is done is finger pressure. greg also used to talk about how the clutch would be put in fast, and the INT plate would "smash" into the "little" H adjusters. no, this is not what happens. push the clutch in as fast as you can and its a very undramtic contact. what is the problem is vibration when the spinning mass of the INT plate is supported by ONLY the H adjsuters. they can very easy move with the high forces involved , axially on the vibrating INT plate at 6000rpm. by the way, one can move more than the others and THEY DO. it causes nothing more than dragging on the Pressure plate when they are out of adjustment. ive had one maxed out and the others at spec. it ONLY takes one to make the clutch drag. they all have to be set at 1mm. By the way, when my clutch got pulled out, several times, including recently during the new car build up, 3years ago, for 7 years that clutch was raced. the clutch discs had the number of the partnumber still visible. basicallly, no wear. and this car is a daily driver too and im not easy on it! im also not living in SF, burning the clutch up every day at hilly stoplights either, but it does show that the mechanisim is working perfectly. the actuator mechnism is the problem now, not the pinning which 4-5 years later, has proven to work fantastically.


Greg, Im not arguing with you about it, but its something you were wrong before about until you DID think about it. A problem with Pinning is only FUD (fear, uncertainty and doubt) there is no LOGICAL reason why pinnning is bad, because the ONLY thing it effects is the INT plates ability to move toward the flywheel and make proper contact with the disc and flywheel forward AS THE DISCS wear. thats it. I adjjust the H's more than ANYONE here, because every time i raced a session, the H adjusters would move. sometimes ONLY one adjuster would move, and the others would be in good position. a few times i adjusted all of the H's and didnt do one correctly and the clutch dragged. it doesnt take much with new components to make the INT plate drag on the pressure plate. just a hair of contact, and it starts it to spin, and wala, you cant get the car into gear. during a race, its not noticible, until you get into the pits and tray and shift.

Bottomline, pinning only effects where the H adjusters are, not balance. even if one was to "break" or "lose a dowel pin", we are tallking less than a mm of position (probably a .5mm as they cant physically more more than this vs the others) . its not enough to change the balance very much.

again, not to argue, just to discuss. I appreciate all the input . I dont know much abouut the clutch hydralic system, other than what ive seen on the manual. Im more concerned with the slave, not pushing the actuator rod far enough, and what the spring function does maybe to keep pressure on the Lever Fork arm?? so that if there was a vibration, it doesnt push the push rod back into the slave, pushing fluid back to the master/reservior??? that now makes the most sense. maybe bleeding it helped, but if there is no spring pressure, vibration can push the pushrod back a little??? are their two springs?? because at assembly contact, there is little or no spring pressure, but i can push the rod back in the slave and it comes back out with normal force, but only to the contact of the arm position. (i.e. not far enough) it makes me think that there are two springs and one is cooked and bad?

heck, maybe it just needed to be bled. Ill find out on a test drive today.

Dutch 928 fan

Had similar symptons that I could not relate to the clutch mechanism either in any logical way. Here's what I did solving it:
1) replace leaking slave
2) bleed and bleed again (attached brake caliper nipple to clutch nipple and pump fluid around and around with brake pedal)
3) adjusted clutch pedal properly according to manual.

Solved it!

Leo 1984 euro s2 5spd

mark kibort

i just went out and tested it on the road. yes, still has the exact problem. i can now have the courage to do it in Idle, just rev slowly to 5k RPM and you can feel the clutch pedal depress on its own and be about half way down. it still works for the shift, but it comes back half way. until the RPM falls, it stays a lpartially depressed.


so, its not bleeding the system.

what did you mean for #2 and 3 above.

mark kibort

so it all sounds like the slave is bad. does everyone think that the spring is bad in my slave and thats the problem? does the spring keep pressure on the lever arm, so that when you depress the clutch, it hasnt backed off due to vibration.

Greg, thanks, you had me second guessing myself here! i went out and checked the INT PLATE. all the dowels are fixed fine, all lthe gaps are 1mm.

UncleMaz

#2 means (from this post https://rennlist.com/forums/5330546-post11.html)

mark kibort

that is really cool. i never saw this post or heard about this. does it just drive fluid up to the reservior and though the clutch master? looks like a great way to bleed or get the air out on a new slave install.

I think the slave has to be bad. the vibration doesnt feel that bad. there is some, but its very slight and i think due to the flywheel being off a little from that wreck, but dont know for sure. bottomline, the slave, even on its own, doesnt push the actuator shaft out very far. as was said, thats a spring function and since its not acting correctly, the shaft is allowed to push fluid back in the system during vibration.

makes me think. is there a pin hole in the master, or slave, where slowly fluid can go back to the reservior?? is that pin hole only engaged when the pedal is not depressed, and when it is, the pin hole is not exposed so that the shaft cant be pushed back?? otherwise, siting at a stoplight, witih clutch pushed in, would eventually allow the car to creep foward as the fluid was pushed back in from the clutch arm pushing on the slave shaft. probably just like the brakes where there is a check valve of some sort to push fliud back ward, but not when you have any pedal pressure. im thinking it must be in the master, because as the pads wear, the position of the pistons would be more extended vs new. but pedal position is always up when you start to push the pads back in the caliper. im thinking the same situation exists for the clutch. correct??

Therefor, as a test i should be able to do the High rpm test with the clutch half depressed, and it shouldnt go south on me. and maybe the spring that is weak, its normal job , is to keep the pressure on the actuator shaft so that vibration and fluid being pushed back is put back as the spring pushs and couteracts this kind of force. Just thinking out loud.