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999 Clutch Stack Height And Plate Count

Discussion in '749 / 999' started by Lucazade, May 13, 2018.

  1. Try dropping the stack hight a little lower, maybe swap a 2mm for a 1.5.

    Did you bleed the clutch at the reservoir?
     
  2. Hopefully that will ease as the plates run in and move more freely in the basket slots.
    There is no positive disengagement of the plates, except perhaps from the spring action of the dished plate.
     
  3. 5mm less makes it slip so I am as low as I can and no idea how long before I have to add 0.5mm

    Old Rider I hope that is what's going to happen
     
  4. As I said, you can always try putting an old plate or two at the top of the stack for a while to make it easier for the plates to separate when you pull the lever.
    Certainly worked for me.
     
  5. i think we need some magic beans...itll be alright then..
     
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  6. Dear Marjorie,

    My 1098R clutch is very grabby and virtually unrideable when pulling away.
    The basket is notched heavily and the dogs on the Friction plates are worn and lipped.
    I could fuck about and post all sorts of shit about it....or...I could just buy new bits and sort it out quietly by myself.

    Oh....the quandary....what should I do??

    Yours Faithfully,

    A Ducati Owner
     
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  7. Dear Ducati Owner
    I can really relate to your dilemma and I strongly urge you to buy a Harley - this way your clutch problems will be a thing of the past.
    Your sincerely
    M
     
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  8. Buying new bits is exactly what he did.
     
  9. Doh! Does that mean I have to buy the bits AND fuck about with postings too??
     
  10. Not all of us can buy new bits at price a Harley each time it does not work. I prefer to buy a Harley or work out my junk :)
     
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  11. Worked for me @Caligas
     
  12. +1 to all of the above.

    I'd always start on the design baseline as a known good datum.
    You know it's correct at the time of assembly and you therefore have a point of reference to say what has changed to cause a problem that wasn't there before.

    Totally Chris, and between your post, @RickyX post above and @andyb advocating start with the basics I done some measuring.

    So...
    On the 749 when i got it, I got told that finding neutral was a pig and the clutch was a right bastard that squealed alot. Ok I thought.. probably just worn plates and air in the system.

    The bike came with an oberon clutch slave and a Ducati Performance clutch pressure plate.

    I took the old plates out and fitted new friction plates.
    The old plates were minus 1 friction which a the time I thought was a bit odd, so I took it all back to design height, and got 38.5 +.4 =38.9 / 39.

    Swapping out a friction and 2mm spacer with a worn friction plates and a 1.5 spacer I got 38.5 on the nose.

    When you saw me Chris, I noted that neutral was still a bastard to find. It wasn't fun sitting at lights with clutch pulled in. Like others, I found that only with the engine turned off it would find neutral.

    More investigation was needed.

    With the bike on a stand and clutch pulled in, the clutch dragged where I should have had a disengagement and been able to turn the rear wheel by hand.

    So in the words of @andyb : what had changed?

    I removed a friction and a spacer plate to achieve disengagement. So stack height was running at circa 34mm now. hmmm - yes it worked, but no, it's not right.

    At this point going through the literature I couldn't find a tolerance range, but Larry Kelly aka shazaam! seemed to think that it was about 2mm. I was sceptical, -2mm yes, but +2mm... couldn't see it.

    So what has changed over standard?

    Oberon slave? I'd had these on my old SS's so I knew that it wasn't / couldn't be the cause.

    Air in the system? OK, I bled the system again and paid special attention to the master cylinder.

    The clutch still behaved in the same way.

    The only other change was in the pressure plate.

    Springs were within tolerance coming in at between 36,5 -36.75
    Old plates were all over 2.8mm... just. (+.03 - .06)

    As @Chris says, tolerances... lets look at some not so obvious numbers.

    So, luckily, I had an old OEM pressure plate in the cupboard.

    First of all we needed some baseline data to make sense of what measuring a pressure plate would tell me, and for that I needed to understand how discrepancies and variations in those figures would relate to the work done by the actuator rod.

    Lets take a stock OE 749s master cylinder:
    15mm bore x 20mm stroke. (15x20)
    Lever length 190mm
    Lever span 95mm
    Master piston travel circa 10mm as a result.
    I couldn't find a bore for the OEM slave, so looking online I'm going with 25mm - which seems to be the common consensus.
    OEM slave cylinder (25mm) linear displacement travel with OEM master cylinder = 3.6mm
    OEM slave cylinder (29mm) linear displacement travel with OEM master cylinder = 2.7mm

    OK, so the Oberon gives up 0.9mm of travel for an easier pull.

    From past experience this isn't enough to cause the design stack height to bind, so we know this is most likely not the issue.

    Lets move on to pressure plates.
    Measurements were taken of the OEM and the DP pressure plates:



    MEASUREMENT 1
    The friction plate contact surface face to the flat inside face of the spring cup:
    OEM 3.33mm
    DP 4.7mm
    +1.4mm difference
    In itself this one bears no relevance until you remove plates.
    On the OEM pressure plate there is a recess for the drum but on the
    DP pressure plate this is completely flat and so it is this face that will bottom out on the hub (pushrod not withstanding).

    MEASUREMENT 2
    Friction plate contact surface to the contact face of the pushrod top hat in the bearing housing:
    OEM 21.3mm
    DP 22mm
    +0.7mm difference

    MEASUREMENT 3
    Friction plate contact surface to the spring contact face:
    OEM 10.13
    DP 11.1
    +0.8mm difference

    pressure plate.jpeg

    So, looking at the results we see the following:
    The DP pressure plate moves the tophat contact face outboard from OEM by + 0.7mm

    This added to the 1mm reduction in displacement from the larger slave = 1.7mm.
    On the DP plate the spring however are already preloaded by nearly another mm before we've even pulled the clutch in so we've now lost 2.5mm of travel potentially if the springs become prematurely coil bound- and when fitted, my springs did indeed look coil bound as per the image above.

    And that's before we've disengaged anything. so lets call that a friction plate gone.
    Then you still need room to disengage the plates, so lets call that a spacer plate in the real world unless you want to have the pressure plate touching a friction plate.

    I also think this was further compounded by the fact that the DP pressure plate would sit deeper inside the assembly by 1.4mm vs the OEM before bottoming out on the hub, so would still be pushing against the plates, meaning that in reality you're looking at the spacer plate definitely going as well, and all the while you're removing travel from the springs as you're compressing them to almost the operational dimension when the clutch is pulled in leaving them with barely any room to move.

    that seems to add up as I had to remove a spacer and a 1.5 friction plate (-4.5mm) to allow the clutch to disengage fully without dragging.


    So the aftermarket pressure plates, if they're made to the DP pattern, by the above numbers will really only be happy working with the stock slave cylinder, as the dimensional stack up with an oberon or similar slave will mean hours of endless fun with removing and swapping out clutch plates.

    I went back to the OEM pressure plate, and it all works just as it should, with the oberon and a full 38.5 stack. :)
     
    #72 Sev, Jun 27, 2020
    Last edited: Mar 6, 2021
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  13. If it’s a slipper the it’s better to measure the build of plates when they are in the clutch And in reference to the clutch with a clearance height ....rather than just a pile of plates!
     
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  14. See my post #24 over a month ago, its the reason I gave up on Oberon slaves, bling pressure plates and open covers. The dry clutches are marginal for reliable and regular road use and don't need any excuses to behave badly.
     
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