My clutch slave cylinder modification

Discussion in 'Crazy-Awesome almost Dakar racers (950/990cc)' started by RedRupert, Oct 17, 2007.

  1. CycleDoc59

    CycleDoc59 Wrench Rider

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    I too found the clutch fluid needs changing frequently.
    ATF seems to work fine. I find frequent fluid changes
    necessary on many bikes with hydaulic clutches, most of
    which use brake fluid.. I figure it's because there
    is very little fluid in the system to disipate moisture, or
    whatever; a fraction of the amount in brake systems.

    On removing the slave, the spacer guide hole
    was somewhat elongated (bike has 18K miles). It was obvious
    that before long it would wear to the point that the piston
    would cock, and cause clutch failure...

    The piston has a projection that fits over the push-rod end,
    and it's a very loose fit. In fact, it's loose enough that piston
    alinement is dependent on the plastic spacer hole; a poor design.

    So I made a bushing for the tip of the pushrod, which now fits
    snugly into the piston end. The piston can't cock now. I'll check
    it every few thousand miles, but I expect it to be fine now...

    Note that since the push rod is a snug fit in the piston, and does
    not move, there will be no friction or wear to consider.

    If anyone can see a pitfall with this solution, don't be shy!
    #61
  2. adiablolex

    adiablolex Lost again

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    Damn Doc, that's what I was trying to get to, haven't decided on material selection yet. I 'm sitting on the fence between rubber and teflon.
    What have you used? :ear
    #62
  3. gefr

    gefr Life is a trip

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    I wonder if the plastic spacer still has the ability to distort ? :ear Waiting for your next check in a couple of thousand miles. Cheers.
    #63
  4. CycleDoc59

    CycleDoc59 Wrench Rider

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    Sorry, ...I forgot to mention what material I used.

    I used a piece of urethane fuel line, about 1/2" long,
    and 3/16" ID. It's a snug fit over the push-rod end,
    but a little too large to fit into the slave piston-end.
    So, I sanded the outside of the little piece of line
    till it would push into the piston.

    Yes, I know, it gets warm down there, but an internet
    search says urethane rubber has a melting point of
    100 C, or 212 F. That should be more than enough;
    we'll see......

    The plastic spacer can't see any more wear, as the
    piston is now fixed to the end of the push-rod,
    and the rod runs in it's own bushings, which allow
    no lateral movement......
    #64
  5. evoluzione

    evoluzione Been here awhile

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    an issue we found when working on our slave cylinder design was that the pushrod is not perfectly concentric to the slave cylinder (too many tolerences between the case, pushrod, slave cylinder, piston & spacer). with your modification it could force the piston slightly off center (only need 0.002" to cause problems). it may work at first but i would be checking the bore of the slave cylinder often for wear.

    just my $0.02.
    #65
  6. CycleDoc59

    CycleDoc59 Wrench Rider

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    Good point...I tried to consider that making the push-rod
    solid with the piston might force the piston to one side or
    the other, just as you suggest.


    That's why I chose the urethane instead of piece of copper
    tubing or similar. I figured the urathane would allow a bit
    of lateral movement....maybe enough to allow the piston
    to stay centered. We shall see.
    #66
  7. RedRupert

    RedRupert Brit in the Soviet Union

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    I'm glad you're testing this idea. I did mention that I had dismissed the idea on the first post of this thread, but I had not thought of using a material soft and forgiving such as urethane. This is what I thought at the time:

    I also thought of using the push-rod to hold the piston straight, but ruled this out as forces from the push-rod may subject the piston, and its seal, to additional stress.

    Good luck, and don't forget to let us know what happens. :ear
    #67
  8. ABYSS

    ABYSS KTM

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    I was the one a that got a hold of Ken and pressed the issue. I then helped rattle the cages here in the OC and we found someone gracious enough to donate there scoot to Ken for the design work that benifited all of us.

    I bought two of these even before they were made and they are both working flawlessly. Even in HOT TEXAS


    In regards the aluminum spacer KEN if you are offereing put me down for two of them.

    While after taking one back off and looking at the desgin I agree that it will not improve performance. I do beleive an aluminium one would be impervious to chemical attack there by eliminating the possiblity of errosion and disfiguring of the spacer. Which would intern premote longevity.

    Thank you again Ken for stepping up and helping us out.
    #68
  9. RedRupert

    RedRupert Brit in the Soviet Union

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    True, and it reminds me of when Honda tried machining the cylinder heads and cam caps separately (1980s). Usually they are assembled and bored together so that they are a perfect match. It was a disaster for Honda.

    The beauty of producing an aluminium spacer to fit your own slave cylinder is that the piston guide hole in the spacer can be positioned in exactly the right place. This was done when we modified my plastic spacer by inserting a brass bush (post 1 and 2 of this thread). The piston guide hole is in exactly the right place. The plastic spacer cannot move in relation to the slave cylinder, as the male rim of the slave cylinder locates inside the well in the plastic spacer. When the slave cylinder is bolted in place, the plastic spacer is sandwiched between the cylinder on one side, and the metal plate on the other side, and clamped in place. The spacer cannot move, and now the piston hole is stable so it won't allow the piston to skew.

    If the modified plastic/brass spacer fails, I shall have an aluminium spacer made, as I no longer think heat adversely affects the rest of the hydraulic clutch system once a higher spec fluid is employed.
    #69
  10. RedRupert

    RedRupert Brit in the Soviet Union

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    I agree that the diminutive amount of fluid may contribute to the premature failure fluid, so how about:

    Producing a simple aluminium chamber that can be installed in the clutch line. Half-way down under the fuel tank, for example. Maybe a cylinder with threads at each end to take standard banjo bolts. Obviously two replacement lines will have to be made up. The cylinder/chamber could have an internal bore that would increase the volume of fluid + the aluminium cylinder/chamber could be attached to the frame so as to use the frame as heat sink? It would be simpler than trying to enlarge the reservoir like the Italian racing team did.

    I don't think moisture in the fluid is an issue. We worry about it in brake fluid, as it lowers the boiling point of the brake fluid, but the clutch gets nowhere near that hot.
    #70
  11. evoluzione

    evoluzione Been here awhile

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    funny you mention this as it is something we designed but figured that the cost (including the new clutch lines) would be more than people would want to spend.
    #71
  12. cpmodem

    cpmodem Orange Caveman

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    Another EVO product perhaps?
    #72
  13. cjracer

    cjracer AWD please!!

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    Something like this?:D
    #73
  14. cpmodem

    cpmodem Orange Caveman

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    CJ. I want one. Where?
    :D
    #74
  15. cjracer

    cjracer AWD please!!

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    Get in line....:lol3 More details soon.:thumb
    #75
  16. cpmodem

    cpmodem Orange Caveman

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    Way to go. Put me on the list.:deal
    #76
  17. ABYSS

    ABYSS KTM

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    looks geat CJ I want one too!
    #77
  18. adiablolex

    adiablolex Lost again

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    Now that my friends is injenuity:clap .

    Fixing the source of the problem will actualy work better.
    I want one too.
    :thumb
    #78
  19. gefr

    gefr Life is a trip

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    Can we have a price estimate?
    #79
  20. riceless

    riceless Let's Ride!

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    2002 KTM 300, bought new, Magura mineral oil only, two years of riding & racing in 100 degrees Fahrenheit, no problem... 2004 KTM 525, bought used, "dealer serviced" previous to me, one year of racing & riding in 100 degrees Faherenheit, slave cylinder failure. Is Motorex mineral oil? If it's not, don't put it in dere! P.S. 2006 KTM 950, bought used...UH-OH!:waysad
    #80