mark kibort

i know, huh!!

no valve stems cant work their way out due to centrifugal force. its just not enough, especially at wheel RPM, which is near 1800rpm at 150mph
the engine has rpm up to 6500rpm , but as was mentioned, the force on that little roll pin is no where near its interfernce fit holding force. not even a concern. and if they did get flung out, the little spec of metal would just fall out the hole and end up on the track somewhere.

atb

Mark,
How did you determine the postion of the "H" for pinning. You say "centered", but how and/or from where did measure to determine that it wasn't too far forward or too far back?

mark kibort

i determined the position by the adjustment procedure. this makes sure it is "centered" . what that means is that at the .75 to 1mm spec gap, you will have about that much room on the rear of the H adusters just incase you get some crazy wear on the discs. (unlikely). rememer you are adjusting the system with the discs clamped against the INT plate , and flywheel.

when you press the clutch pedal, the flat springs are what chase the pressure plate rear ward, and the H's only job is to stop the intermediate plate from traveling too far rear ward. too far, and it doesnt lose contact with the pressure plate surface. main shafts continue to spin, and you cant get the car in gear. adjusted properly, and the inermediate plate moves only 1mm or so rear ward, not as far as the pressure plate is retracted and you have a main shaft that is not spining, and it goes into gear correctly with no drag.

I pin the H's at that point of perfect adjustment. just drill a hole at near the H's axis point and put in a roll pin tapped in with a drift. fixed for life!

mk

wildwestsydney

Tomorrow I will have my 5spd back on the road and I have moved my H tabs all the the way back I will report in as to my shifter function.

Vilhuer

Not really. If you do this when both disks are new area where intermediate plate can move is not enough for entire disk wear range. Thats reason why factory did sliding H setup and not just simple fixed setup. By fixing three H into one position it will not allow intermediate plate to center within available space when pressure plate is moved back by clutch fork.

When H piece tightness is correct and they can move this will stop intemediate plate to position where both disks will start to bite around same time and thus wear evenly. Fixed H will work at least part of the disk wear movement but clutch is not exact same what factory intented as soon as disks wear from thickness where H were fixed in place.

mark kibort

It sounds like you dont understand the function of the release of the interemediate plate via the flat springs and the pulling back of the pressure plate via the clutch fork. when the clutch is pressed in , the pressure plate releaves "pressure " on the system of discs intermediate plate, on to the flywheel. the int plate doesnt need to "center" itself, it just needs to be able to back off a mm or so, to not continue to put any pressure or frition on the front disc and flywheel. ths is the easy part.any movement rearward willl do this thas why a small gap will work too. (less than.75mm, but greater than about .5mm) as long as its releasing from the front, you are golden. the smaller the gap, the more wear you will be able to sustain in the discs and still have everything work just fine. the rear ward movement now, is controlled by the H adjuster limit, and thats not any issue at all because the pressure plate is pulling things rearward much farther than the H tabs are allowing the INTplate to move rearward via the flat springs. too large of a gap and the int plate moves rearward with the spring pressure of the flat springs and it can slightly rub on the rear clutch disc and the pressure plate friction surface. this is when you cant get it in gear.

if you pull the H's all the way back and it does work, you are lucky. it means the pressure is pulling back further than the H's allow . it also means you might have a long throw clutch pedal too. but, it also means that the clutch intermediate plate migh be restricted from making pressure forward, with the forward discs , and that might be fine for a while, until they wear, and if the presssure plate cant actually self move the H adjuster, you will have a slipping clutch. not enough forward disc pressure on the flywheel. if this is the case, your system is self adjusting, and this is due to the pressure plate making more rear ward movement than the systems Ive worked on on several cars. (where the 1mm max gap needs to be preserved. any wider, and it causes an impossible gear engagment.

Why do you think i have this issue in the first place?? the system vibrates, as the intermediate plate is spining and pushes the tabs near max position rear ward. after a race, my car will not go into gear unless i re-adjust the H tabs to spec. this is the reason that Porsche designed it that way in the first place.

again, by locking the H tabs in perfect adjustment, you allow for lifetime pull back of the intermediate plate function. never a problem there, but a limit of about 1mm of wear on the front side discs, which ive never seen. But, certanly it is possible, and at that point the engagement would be limited by the restricted distance of the "pinned" H adjusters. but if you got discs that are half worn, you have reduced clamping force off the pressure plate anyway, so its time to get in there and buy and replace new discs.

Vilhuer

So you basically rather change disks twice as often than needed instead of properly fixing intermediate plate problems caused by worn part. If you can't use disks all the way to the end your pressure plate is also too weak.

mark kibort

if you know how to drive a stick, you wont wear the clutch out over 100,000miles or more.

if you do, and the discs are half worn, you might have an issue, but if they were worn that much their gripping force woudl be greatly reduced anyway. thats just because the stock pressure plate is fairly weak anyway.

the main answer to your statement, is that yes, i would rather replace clutch discs at $100 when they are half worn. (ive never even seen that much wear on any clutch disc by the way), then have to replace an intermediate plate which now are near $700. I think that is the logic ive been using and its serviing me well. the bottom line, i had a wasted intermedate plate . I needed a new one, but instead, for 3 years , and a lot of racing, with no real worries in the forseable future, i have a working clutch and all it cost me was 3 little roll pins.

atb

Alright Mark, picked up my roll pins today. Did you trim them down to fit, or did you keep the excess on the inboard side to give the pin some runout if it moves? If you didn't trim them, what width did you use? I've 1" and 1/2".
Thanks.

hacker-pschorr

I see the point of doing this, but only if you have an intermediate disc that is not holding adjustment.

mark kibort

yes, and most,even bad ones, will work for agressive street driving. mine and scots worked fine to and from the track. after the first session, better not stop and put it in neutral......... anyway, it wasnt quite that bad, but certainly after the weekend, it had to be adjusted. scots got so bad we just replaced the INT plate with a newer used on. to your point , its working fine now.


no trimming. you want it sticking out a little, so i want to think i used 1" long pins, but ill have to check. you dont want it to go too far on the inboard side, or it will inhibit INT plate movement. just enough so it penetrates the moving part and the other side. I really dont remember. so, ill check my spares . they might be 1/2", or even 3/4".

hacker-pschorr

The intermediate disc in my 79 has decided to stop cooperating. One of the 3 adjusters won't hold position anymore. It looks like I'll be trying the drill / roll-pin option here this weekend.

mark kibort

awesome! it's a great fix and still, after 15 years, mine is working fantastic....meaning NO ISSUES. and man, it was so frustrating that year of racing to not be able to put the darn thing in gear without turning off the engine. (adjusters moved all the way back because they were weak ) so, find the spot where they are adjusted about 1mm gap... drill and then put the roll pin in there. off the car, might be a challenge to know where that position would be, but i guess you adjust it on the car, mark it with a good method of marking, and then drill and plug out of the car. i got a very long drill bit to do this and was able to do it on the car, which guarantees success. let me know how it goes.. soon, 1000s of pefectly good intermediate plates that have nothing wrong but weak rivits on the adjusters, will be available to the 928 community!

GregBBRD

I'd sure like to know where those thousands of intermediate plates are sitting....

Vilhuer

We did this 25 years ago. Still works as factory intended.