KTM LC4 625 SXC Brake Issue

Discussion in 'Thumpers' started by DirtMerchant, Oct 8, 2007.

  1. DirtMerchant

    DirtMerchant Long timer

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    Aug 2, 2004
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    1,624
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    Well,

    I ran into a little bit of an issue.

    When I took the bike for a ride today the front brakes were draging; not real bad but they would have locked had I gone much further. I opened the bleeder and let the pressure off and all was fine but lever is not nice and tight again.

    What did I do wrong or what didn't I do? :ear :ear
    #21
  2. Ducky 149

    Ducky 149 Been here awhile

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    Oct 20, 2006
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    Hey Dirt, Sorry to hear of your brake malady. My 03 625 SXC has a crappy front stopper also. I was going to try to vacuum bleed the system with a Mityvac hand vac pump. If that does not bring joy, then I think a new master cyl seal is in order. I think the lip seal in the master is slightly pulling away from the bore of the master cyl itself causing some sponginess before it reseals (sort of) during application. I have tried the reverse bleeding (knee on caliper). Also no joy. I have owned the bike since new and it has gotten progressivly worse. That is what makes me think the mstr cyl seal is checking out. Please keep us posted and I will do the same.

    Ducky
    #22
  3. DirtMerchant

    DirtMerchant Long timer

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    I used the zip tie around the lever and grip trick and the lever was as tight as a German virgin :deal Problem is that the bads started draging once the brakes warmed up. That could have gotten real ugly if it had locked up..... :huh

    I ordered a front brake switch from Baja Designs; when I get that in I am going to drill a couple extra holes and then try the zip tie again. :dunno
    #23
  4. redveloce

    redveloce Been here awhile

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    Most likely your return port in the reservoir is plugged. It's a pin sized hole that allows fluid to return as pressure builds from heat. It can also keep the brakes from bleeding properly. I had the same thing happen on an old Honda and the front locked on me at 40mph.

    I was able to get rid the spongy feel in mine by forcing the caliper open pushing on it with my foot. The lever was solid when I got it pumped back up. Try that. If the caliper won't move then it's definitely your return port.<o:p></o:p>
    #24
  5. DirtMerchant

    DirtMerchant Long timer

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    Thanks, I will give that a try. I have a pressure switch in the mail from Baja Designs so I will everyting apart when that arrives in a few days.

    Rodney

    #25
  6. DirtMerchant

    DirtMerchant Long timer

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    Okay fellows, I am still having an issue with pressure building up in the front brake system. :huh

    When riding on ROUGH roads the front brake will build pressure as if I were pulling the lever; this is with only slight front brake use. I have to stop, have my riding buddy pull the lever while I crack the bleeder to let the pressure off and then I will be good for a few miles. :deal.

    Redveloce mentioned earlier that it may be the return port plugged. Anyone have any experience with replacing or cleaning this?

    One thing that I think may be important to note is that when this happens the pressure switch is activating the BRAKE LIGHT. I did slightly overfill the the master a bit; could that be an issue?
    #26
  7. bmwktmbill

    bmwktmbill Traveler

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    Dirt, call me crazy but cant you see the return port(s) with the top off the rez. You maybe get a little bubble when it works right and you are bleeding.
    Stick something in them to make sure they are open. Needle, wire somesuch(be gentle).

    I don't remember if there is one or two and I don't have access to my bike to check.
    Also as suggested make sure the piston is returning fully at the end of each actuation.

    Man if it was me and the ports are open I would rebuild the master or at least disassemble and clean and look.
    Something is F'd up.
    You gotta have brakes.
    The KTM 640 is known for great front brake(s).
    It's a simple mastercylinder.
    You are gonna wreck your pads and rotor.
    b.
    #27
  8. DirtMerchant

    DirtMerchant Long timer

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    Bill,

    Thanks for the suggestions; I'll report back with my findings.
    #28