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Excessive brake lever travel

Discussion in 'Tech' started by dudutzu, Oct 11, 2021.

  1. dudutzu

    dudutzu Well-Known Member

    Hey everyone,

    Looking to see if anyone here had this happen to them and know how to remediate it(other than "bleed the brakes").

    When I first use the brakes after cleaning the pistons(or anytime I move the pistons in or out for any reason, like front wheel changes, caliper cleaning, etc) the bite/pressure build up/engagement point is right there, almost no lever travel. However, over time(sometimes over 2 trackdays(if it's hotter outside), sometimes 4 trackdays) the bite point moves closer to the bar, brakes are still FIRM/work them same, but the bite point moved(about 1/2").
    And once it reached that point then it doesn't change any further.
    The travel distance stays the same no matter the temperature or whether bike is moving or not. Brakes are NOT squishy! Cannot be pumped up.

    Best I can come up with is that the seals are getting stuck to the pistons and pulling the pistons in too far, but soon as I move them - that position is reset and the cycle starts over.
    Is this a seal and/or caliper design issue?

    Calipers are nissin monoblocks from a 2019 zx6r that I got pretty much with no miles on them, it's been doing that from day 1.
    I fully disassemble, clean and lube the calipers every 10 days or so and clean the pistons(without removing) every couple events(vesrah's are dusty). I tried using brake fluid as assembly lube and tried using caliper rubber grease - no difference. Different rotors didn't make a difference either.

    Thoughts or ideas?
     
  2. wheelz96

    wheelz96 Well-Known Member

    Bleed the brakes.

    I know you don't want to hear that but I think it's common to rebleed after multiple track days or races. What brake fluid are you running? I have to rebleed my racebike after each weekend and sometimes during the weekend if I do alot of heavy braking. The fluid will get hot and start to boil which creates air bubbles and that is the feeling of compressed air in the lever. You hinted it happens more often if it's hotter outside. This helps boil the fluid faster.

    If I am wrong about this then you are not the only one who has to rebleed brakes often. It could be a minor air leak in the system or maybe the seals in your calipers but I have always dealt with this. I think this is more common then you think. I'm on a stock M/C with RBF600 fluid, steel lines, Vesrah pads, and deal with this too. We all deal with this on the race team. Brake fade is real and is why they make adjusters to move your lever further or closer to the bar.
     
    dudutzu likes this.
  3. dudutzu

    dudutzu Well-Known Member

    I'm not discounting the possibility of air in the system, but I tried bleeding them when the travel increases - I wouldn't get any air and no improvement in lever travel.
    Motul 5.1
    It just doesn't feel like air in the system(but it's possible I just don't know what that feels like(no sarcasm)).
    Lever is always firm once engaged.
    The reason why I'm leaning towards not being air in the system is that if there was air in the system, then why is that when I barely push the pistons in during the front tire change - the lever returns to normal?
    Maybe like you said - maybe it's normal...
     
  4. JCW

    JCW Well-Known Member

    A master cylinder issue?
     
  5. Pneumatico Delle Vittorie

    Pneumatico Delle Vittorie Retired "Tire" Guy

    If everything is good mechanically I would bet there's moisture/contamination in the system from either too much time on the brake fluid or from new brake fluid that wasn't up to normal spec. So to fix all of the variables, clean the whole system, check all of the seals, and spend extra time filling and bleeding the new fluid! And always add fluid from an unsealed bottle.
     
  6. Mechdziner714

    Mechdziner714 More Gas Less Brakes

    Hows the rotor? A warped one can push the pistons farther out making the travel longer to get bite.
     
  7. dudutzu

    dudutzu Well-Known Member

    I agree with that, however wouldn't that happen soon as I get rolling, instead of days? Also at standstill, since the rotor isn't moving, it should pump up and feel normal, right? but it doesn't...
     
  8. dudutzu

    dudutzu Well-Known Member

    I thought I was already doing all that you suggested, but maybe not.
     
  9. DonTZ125

    DonTZ125 Purveyor of Neat Toys

    Don't you mean an unOPENED bottle?
     
    sbk1198 likes this.
  10. Mechdziner714

    Mechdziner714 More Gas Less Brakes

    Its hard af to pour from an unopened one...
     
  11. Pneumatico Delle Vittorie

    Pneumatico Delle Vittorie Retired "Tire" Guy

    Brain fart and yes! When I used to sell chemicals at Tucker Rocky I did run into new brake fluid bottles that weren't sealed correctly at the factory so moisture did ruin the product
     
  12. DBConz

    DBConz Registered Idiot

    so i had this issue all season and it took a while to figure out my issue.

    i rebuild two sets of calipers and masters. lever kept getting soft.
    i zip tied the brake lever overnight to see if there was fluid leaking out, which would cause air to come in. turns out my OEM bleeders went bad. i kept seeing fluid seeping out by the threads and this was after torquing them to spec (yea there is a torque spec for bleeder screws). once i put new OEM bleeders in and zip tied the lever overnight again, no fluid was found! now my lever is consistent again.
     
    dudutzu, TurboBlew and JCW like this.
  13. TurboBlew

    TurboBlew Registers Abusers

    Was this on a GSXR or another model? Usually on street bikes the bleeder screws rarely get touched... on track/race bikes they seem to be a wear item.
     
  14. JCW

    JCW Well-Known Member

    Old news, I know, but the gsxr also had a strange condition with the MC where gas would be produced through some sort of chemical reaction in the piston/bore.
    doesn't sound like what's happening here since he states simply changing front tires and pushing the pistons solves the problem for a while...


    1 / 7
    Service Bulletin SUZUKI MOTOR OF AMERICA, INC.
    3251 E. Imperial Hwy, Brea CA 92821 USA
    MOTORCYCLE DIVISION

    GS/GSX/GSX-R NO. 228

    DATE: 10/28/2013
    SUBJECT: SAfETY RECALL CAMpAIGN — fRONT BRAKE MASTER CYLINDER
    MODELS: 2004-2013 GSX-R600
    2004-2013 GSX-R750
    2005-2013 GSX-R1000

    102813-suzuki-gsx-r-recall-master-cylinder-diagram.jpg

    This notice is sent to you in accordance with the requirements of the National Traffic and Motor Vehicle Safety
    Act. Suzuki Motor Corporation has decided that a defect which relates to motor vehicle safety exists in certain

    2004-2013 model Suzuki motorcycles listed above.
    What is the problem?
    After a long-term service life of the motorcycle without changing the brake fluid, the brake fluid can deteriorate
    and absorb moisture. The brake piston inside the front brake master cylinder of some motorcycles may not have
    uniform surface treatment. This combination of conditions can lead to corrosion of the brake piston. Corrosion of

    the brake piston generates gas, which may not be adequately purged from the master cylinder due to the side

    position location of the reservoir port. Gas remaining in the master cylinder can affect braking power by reducing

    proper fluid pressure transmission to the front brake. Over time, as gas continues to slowly accumulate above

    the reservoir port, the front brake lever may develop a “spongy” feel and stopping distances may be extended,
    increasing the risk of a crash.
     
    Last edited: Oct 11, 2021
  15. DBConz

    DBConz Registered Idiot

    GSXR race bike
     
  16. dudutzu

    dudutzu Well-Known Member

    The stock master on mine is also a nissin but it's the newer style, the one with the reservoir port at the top, thank you tho!
     
  17. dudutzu

    dudutzu Well-Known Member

    I wouldn't say my lever was getting soft, but I'll give it a shot - it's easy enough to try. Thanks Jim!
     
  18. DBConz

    DBConz Registered Idiot

    just re-read your issue. if the lever is still the same stiffness but less brake bite, have you changed brake pad brands a few times? have you scuffed up the rotors? i'm wondering if the rotors are glazed a bit.

    how worn are your pads?

    also, you want to be on RBF600. use the 5.1 for a street bike.
     
  19. dudutzu

    dudutzu Well-Known Member

    Same stiffness, same bite, but different engagement point.
    Same pad compound all year, still have 3mm of pad material on them(3.8mm when new)
     
  20. JCW

    JCW Well-Known Member

    Maybe check rotor run out. I know you said it happened after rotor change. Maybe the wheels mounting surface is warped?

    If not, I'd replace the MC. even the replacement was just not best quality...
     

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