Imo000

OK, that I see. So a properly set up single disk feels just like every other high HP (higher than 150 hp) single disk clutch, but a dual 928 has it's own feel?

Mine is almost like a singe, and I have glazed it before the SC went on (somehow it went back to normal after a day ofr driving). Having said that, the engagement and release point is slightly different than a single disk, but not a 928, car.

wildwestsydney

Took the car for a spin today. I think after the adjustment I made the clutch is a slight bit better. One more thing I noticed was that the pedal has about one inch of free travel at the top. I will look into the free travel.

I was doing standing starts in a empty high school parking lot and thought to myself If several 5 speeds could be brought to one empty parking lot then each owner could try other cars out and feel the clutch. I am on the south shore of massachusetts if any five speeders out there want to organize a clutch feel session I am in.

Sam

jackson101

The TOB might be sticking on the guide tube. You push the clutch in, release and get a bit of a delay before re-engagement, as the bearing TOB is dislodged from the tube and moves forward. Also, check the assist spring adjustment,......43 MM ??? I think, from the back of the spring to the center of the link pin.

SharkSkin

I usually don't pay that much attention, but for the sake of this discussion I did today.

I can first feel my clutch begin to grab maybe 1/4 to 1/3 of the way off the floor. This is the point where the pressure plate is pressing the rear disc against the intermediate plate, which is resisting with the very light force of the three springs around the perimeter of the IP. Where this occurs is(assuming all parts are good, hydraulics bled) a function of the state of the hydraulic system, the thickness of the rear disk, and the position of the adjusting forks. With a wide gap this occus closer to the floor; with a narrower gap it occurs further off the floor.

My clutch begins to bite with the pedal about halfway off the floor. This is the point where the pressure plate has pressed the rear disk against the IP and the IP is beginning to clamp the front disk against the flywheel. The difference between this point and the point where it first grabs is(same assumptions) affected by the position of the adjusting forks, and the thickness of the front disk. With a wider gap, there will be a greater difference between the "grab" and "bite" points. With a narrower gap, the difference will be smaller.

My clutch is fully engaged by about 2/3 -3/4 of the way off the floor. The difference between this point and the initial "grab"[Edit: Meant to say "bite"] point is generally due to the springs within the friction disks and the springs in the pressure plate having to reach a point where there is enough preload on the springs to press all of the linings and plates together with enough force to prevent slippage. [Edit: The amount of travel between "bite" and "engaged" cannot be adjusted.] If I had 200 more horsepower, I would probably need to let the clutch out a bit more to perceive that it has engaged to the point where it doesn't slip; in practice this difference may be too small to detect without some way of measuring actual pedal travel.

IMHO my setup is a bit tighter than other 2-disk 928 clutches I've driven, but is looser between initial grab and full engagement than a typical single-plate clutch(I haven't driven a single-plate 928 so can't offer a comparison to that).

If you want to reduce the clutch travel between initial grab and full engagement then you need to minimize the gap at the adjusting fork. You may have luck with a 0.5mm gap or less, but that's pushing it IMHO. Bottom line, you should be able to go from idling in neutral, push in the clutch, count one-two and put it into reverse without grinding. If this test fails you have to figure out where it's dragging.

Others may have different behavior depending on condition of parts, adjustment, etc. but here is one data point.

mark kibort

Dave, I was kind of thinking along these lines, until more testing and experience, seemed to conflict. I think, (and this is my opinion) that the intermediate plate has no bearing on the release and engagement point. I say this, because when I beat the darn thing on the race car in race conditions, I will shift those forks, ("H") to widen the gap. meaning, the int plate is now allowed to make contact on the pressure plate, not allowing for me to get the car into gear. (this happens about every 2 weekends, or 6 times on the track. havent been able to create the same forces on the street to move them) The pressure is only finger pressure as far as force, but its enought to spin the torque tube with clutch in, and car stopped. Under racing conditions, the shifting is almost unnoticeable. the easy shifts when driving the food market are tougher, as i need to have the shift to the floor for smooth shifts, but the release points dont change. (from what I've seen) This makes sense because the flat spring pressure is finger pressure. (10lbs of force) compared to the hundreds of lbs of force that the pressure plate applies to the system.

Again, this is my observation and I certainly dont want to get in to a heated debate again over nothing, but I think the major difference is the slave action, bled lines, ball socket parts condition, and pressure plate and disc condition. maybe alignement of the clutch intermediate plate. If its angled and not even at all 3 adjustment points, maybe that can change things too.

as another note, ive also used the .5mm (or smaller ) gap. all that did was not allow the INT plate to retreat from the flywheel creating the same drag and characteristics as too wide of a gap 1.3mm or greater (I use just less than 1mm)
However, once moving there was no real difference in engagement and release points, again, this is because the spring pressure of the INT plate is only about 10lbs. not enough to effect engagement points, but certainly enough to spin the torque tube when you dont want it spinning. (i.e. with you stopped and trying to get the car in gear with the clutch depressed)

mk

SharkSkin

Mark, I never meant to say otherwise. I see that I made a mistake in my 4th paragraph, I will go back and correct it. Please go back and read carefully. Maybe I could have been a bit clearer overall, but didn't want to bury the important points in a lot of verbiage -- I was talking about 4 specific points along clutch pedal travel:

Disengaged: Inferred, not described directly. Clutch pedal is to the floor and there is no rotational force transmitted to the drive shaft.

Grab: The point where you first feel something try to grab and twist the drive shaft; enough force is being transmitted to the driveshaft to grind going from neutral to reverse, but nowhere near enough to move the car. You will not feel this point on a misadjusted, dragging clutch because you are already there. You will probably not be able to feel this point once you are moving and shifting gears, and you will almost certainly not feel this in the heat of battle, on the track.

Bite: The point where the clutch is beginning to actually "bite" and transfer enough force to begin moving the car forward.

Engaged: Should be self-explanatory -- the point at which the clutch is no longer slipping, flywheel and driveshaft moving at same speed transmitting all power to driveshaft

What I meant to convey to Sam is that you can alter the amount of pedal travel between "grab" and "bite" by moving the adjusting forks, with the caveat that if you move it too far the clutch will drag.

I did not mean to in any way imply that the amount of pedal travel between "bite" and "engaged" can be altered by adjusting.

mark kibort

I see. hmm, "grab and bite" adjustment. Yeah, kind of. Here is an easy test. when the forks are way out of adjustment, I can put the car in gear and start it andhave a little tiny bit of force pulling forward, unless the pedal is all the way to the floor. So, I kind of buy that. Also, I can try and force the shifter into gear, even though it is stuck. as you press against the synchos, trying to match the gears, you get a little force, probably that being the 10lbs of spring force in the intermediate plate. its is very light, but I see your point. Yes, night and day when its all working well for leasurely shifts, but racing, not so much so at all.

I do like the definitions. Now, If I can just get clutch "engaged" and "disengaged" straight, Ill be half way there!

mk

SharkSkin

I came up with the definitions sort of on the fly... IMHO "bite" is common nomenclature both for clutches and for brakes, but in order to help Sam quantify the differences between what he's seeing and what he expects vs what I'm seeing(and maybe others) I had to come up with something. AFAIK there is no "official" way to describe the different points I mentioned so I just came up with something for the moment.

Certainly what I put down is subject to interpretation or change by the community at large but if we can stick to the above within the confines of this thread and until Sam is comfortable with what's going on then it may be useful.

wildwestsydney

Very good definitions, Webtster's could not have done a better job.

Dave and Mark you are both making excellent points. I think one thing is for sure Porsche could have done a better job with the two disk clutch setup.

Way back in the day, mid eighties, my father ran a new england style "pro stock" circle track car. He ran a multi disk clutch hydraulically actuated, that sucker was on or off very little slip and a very stiff pedel. I was expecting the 928 clutch to be more like that. I also have quite a bit of experience with multi disk motorcycle wet clutches, which I think work very well.

I will continue to adjust an hopefully get the clutch to my liking.

thanks for all the input thus far.

sam