Clutch Problems

Discussion in 'Thumpers' started by 1stworks, Apr 17, 2006.

  1. meat popsicle

    meat popsicle Ignostic

    Joined:
    Feb 9, 2004
    Oddometer:
    14,567
    Location:
    Circumlocution Office of Little Dorrit
    Thanks for the tip - master cylinder is original too (slave o-ring looked and felt ok... but it had to be bad because clutch fluid was disappearing without an apparent external leak) so I need to get a few spares before next week's Wednesday departure.
    #41
  2. RedDread

    RedDread What I can While I can.

    Joined:
    Mar 14, 2007
    Oddometer:
    32
    Location:
    Idaho
    Looks like over the last few years at least 3 of us have had the same clutch issue. I suspect mine was spurred on by getting too hot. Have you guys taken any drastic cooling measures with your bikes like higher volume coolant systems, second fan kit or modified coolant?
    #42
  3. meat popsicle

    meat popsicle Ignostic

    Joined:
    Feb 9, 2004
    Oddometer:
    14,567
    Location:
    Circumlocution Office of Little Dorrit
    I've been told the KTM clutch slave is crud, and some highly recommend one of the aftermarket parts (I think there are two mfgs who make them). The cited issue was that the piston doesn't stay perpendicular to the bore; poor design. Maybe your thought is good too - can be a cluster-F of problems.

    I have the 640A so its got oil in frame. I have not seen many who have gone aftermarket radiators. Some have done alt coolants (WaterWetter etc.) but remember that if you up the coolant's specs you have to up the radiator's specs or the coolant will simply overheat easier. The coolant system is balanced by the engineers, which I learned the hard way.
    #43
  4. RedDread

    RedDread What I can While I can.

    Joined:
    Mar 14, 2007
    Oddometer:
    32
    Location:
    Idaho
    So is this to say you don't recommend the second fan? Seems that this may be an effective way to increase the efficiency without destabilizing run balancing system. Your advice in the past has been solid, so I'd really like to clarify if you think adding the second fan kit is a bad idea, or that changing the radiator and coolant specifications would create more issues.
    #44
  5. meat popsicle

    meat popsicle Ignostic

    Joined:
    Feb 9, 2004
    Oddometer:
    14,567
    Location:
    Circumlocution Office of Little Dorrit
    Sorry, the second fan will not cause a problem, because it just helps the radiators shed heat when you are not going fast enough. That is at the end of the system. But changing one of the intervening steps such as a higher efficiency coolant without improving the radiators ability to shed heat (even at speed) will destabilize the system. My bike's engine may be running cooler because of Water Wetter, but the coolant runs hotter or overheats easier because the stock radiators can't shed the heat fast enough. Maybe a second fan could improve things enough; maybe not.
    #45
  6. ChasingBorders

    ChasingBorders n00b

    Joined:
    Oct 2, 2017
    Oddometer:
    6
    Location:
    Oslo, Norway
    Hey guys, I'm travelling through Africa on my 2007 640A, currently in Kenya. I'm in real need of some assistance! I'm experiencing troubles with my hydraulic clutch which I just cant figure out.

    It started with the clutch lever loosing resistance and fluid in master cylinder dropping, meaning to me that the seal in the slave was leaking. I replaced the seal, which lasted for a while but then the clutch startet acting up again.

    I now thought it could be a problem with the master, so I rebuild it with a new piston. That seemed to help, but not for long. The clutch lever would loose resistance after just a few km of riding.

    Eventually I bought and installed a new stock slave sylinder. That made the clutch lever a lot firmer and holds the pressure, but after about 20km of riding the lever would have some play in it. About 1/8 of play of the levers travel. But if I pump the lever a few times the play is gone.

    After 1300km of riding like this the play is getting worse. Now the lever looses almost all pressure. The clutch only disengages when the lever is pulled all the way to the handlebar. And if I pump the lever, the pressure builds up again. It happens in any speed and RPM range.

    The fluid level in the master has not changed the last 1300 km. When I bleed the system, no air comes out of the bleeding screw on the slave, but there are bubbles coming up top in the master. I have checked the crank case and head breather vents for blockages, there are none.

    What can I do? Is my master cylinder broken somehow? Someone told me there's just air in the system and needs to be bled properly. But personally I doubt that's the case, however I don't know much about hydraulic systems.

    I really hope someone here can get me on the right track!
    #46
  7. RideFreak

    RideFreak Torque Junky

    Joined:
    Apr 17, 2009
    Oddometer:
    13,848
    Location:
    Out in the NM Dez somewhere
    If your not losing fluid but you're loosing lever pull then the master is bad. Since it's recently been rebuilt then I'd look close at the M/C bore, it's probably wore. Might be time for a new one.
    #47
  8. ChasingBorders

    ChasingBorders n00b

    Joined:
    Oct 2, 2017
    Oddometer:
    6
    Location:
    Oslo, Norway
    Thanks for the reply.

    I noticed yesterday a very small scratch in the bore, but as it's not leaking fluid I figured it wasn't an issue. But that could be it. I will try with a new master.
    #48
  9. RideFreak

    RideFreak Torque Junky

    Joined:
    Apr 17, 2009
    Oddometer:
    13,848
    Location:
    Out in the NM Dez somewhere
    The master probably won't leak even though it's bad, what happens is the oil gets forced past the inner piston in the MC which reduces it's ability to pressurize the slave cyl.
    #49