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Brake issue?

Discussion in 'Motorcycle Talk' started by mulletman, May 15, 2012.

  1. Okay, this one has me a little puzzled.

    The bike is my '05 GSX-R 600 track bike. It's very much new to me, so unfortunately I don't have a whole lot of history to this problem.

    I've recently experienced some softness and excessive travel in the front brake lever... I thought no big deal, needs a brake bleed... So I do a brake bleed, and flush a fair amount of new fluid through the system. Calipers, master cylinder, everything. The lever is now nice and stiff, and consistent. I close everything up, and re-position the bike back in the corner of the garage. As I'm moving the bike forward/backward and moving the forks from side to side, I notice again that if I squeeze the brake lever it goes soft and I can pull it most of the way to the grip. If I stop moving the motorcycle and squeeze it again it feels perfectly normal. I can leave the bike in the same place for a week or more and it will feel perfect from the first squeeze. If the bike is in motion, not so much.

    While test riding at low speed, the brakes have plenty of bite, are nice and progressive, and provide normal stopping power. No shaking or pulsing, but with occasional strange lever feel.

    I know the brake bleed job likely isn't the issue, as I've done that before with good results, and this bike was exhibiting the same behavior before and after I bled it. Warped rotor? What gives?

    Trying to make it to the track on Friday....
  2. Leak in the system some where?

  3. Doesn't appear to be.... but if there is a very small one I guess I wouldn't really be able to tell. Hmm. Brake system is stock except for braided lines.
  4. RedKat600

    RedKat600 Vintage Screwball Staff Member

    Could be a leaky bleeder screw not seating all the way. Had this happen on my Kat. I noticed when I put the rubber cap on it would bubble down by the threads allowing air into the system. Put a drop of something on the threads, pull the little rubber cap off, when while you put it on look for bubbles at the base of the bleeder screw.
  5. Lone Rider

    Lone Rider Streetfighter

    softness+ lever travel + braided lines+ 7yr old track bike. Could it be Master cylinder piston suffering blow by (worn out)?
  6. theJrod

    theJrod Racer Extraordinaire

    Your symptoms are perfectly inline with a warped rotor.
    Get it up on a front stand and spin the wheel while eyeballing the rotors. You should be able to see it.

    You can probably fix it by hand if you can locate the high spot.
  7. Spun the wheel on a stand, everything looked straight. I also rode it around a fair bit, and the lever stayed consistent. I think you guys are on to something with the tired master cylinder... In any case the brakes work fine and everything is good. I was probably making it out to be a bigger deal than it was. But it also gives me an excuse to buy Brembo stuff soon, haha.

    Signing up for Friday. See you there!
  8. Hmmm. I have extra calipers, pads, stock brake lines and master cylinder for that, I'll bring with me on Friday.

    (I'll just give them to you for free.)

    Maybe it'll help you diagnose the problem?
  9. Good on you for doing that. I would be highly skeptical of a bike on the track with possibly bad brakes.
  10. DGA

    DGA Moderator Staff Member

    Pump up the brake lever and cinch down on it. If it slowly moves towards the bar, without stopping, the MC is bad; the seals are letting the fluid by internally.
  11. You're awesome. Tried to rep, didn't work.

    I wouldn't ride the thing one lap unless I was 100% that it was working very well. I'm paranoid like that. The thing stops hard, and feels good. Another part of this may be the fact that I have extremely limited seat time on this bike as of now.
  12. cobra525

    cobra525 WMRRA Sportsman of the year

    I say welcome to Suzuki breaks
  13. You know, you're probably right. Haha....

    (Still light-years better than my old Honda brakes.)
  14. +1

    Use a big rubber band or a bungee cord so it will have a constant pressure ail the way to the grip.
    Sometimes if you pull gently it will slowly pull all the way in. If you pull hard and fast the bad seal can temporarily seal it's self and stay firm.

  15. I did all of that, it works fine.
  16. DGA

    DGA Moderator Staff Member

    Time for new brakes.

    I know it's not the same, but I replaced the brakes on my old '04 ZX10 with the MC and calipers from a ZX14 and it made an enormous difference. The old ZX10 brakes were always crap, even new. Maybe you are faced with the same.
  17. theJrod

    theJrod Racer Extraordinaire

    I have a spare stock '06 master cylinder that I'll have with me at the track on Friday if you want to try it.

    In fact I think I have enough spares to replace the entire braking system if needed!
  18. do a run-out on your front rotors. if warped or bent, you may not feel it but it will expand pads farther away resulting in deeper pull to engage or a soft feel. Had this on a friends gsxr couple years back.
  19. DGA

    DGA Moderator Staff Member


    Put the bike on a front stand, tape a screw driver to a bucket, or something like that, put it close to the rotor, spin the wheel, and look for deflection. It works like a cheap run-out gauge.
  20. ^^^THIS^^^ is the first thing I though with your description. Time for new rubbers; I might even be tempted to replace the rubber in the calipers.
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