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possible front master cylinder issue?

Discussion in 'Tech' started by MELK-MAN, May 23, 2014.

  1. MELK-MAN

    MELK-MAN The Dude abides...

    i know a failing master cyl can get spongy, and allow the lever to come back to the bar if you keep constant pressure on it (or pedal to go all the way down on the rear).
    But if a 2008 stock r6 brembo master cyl (oem) is worn, could it cause the front calipers to not retract as fast as they should ?
    Only other variable is i used some maxima dot 4 fluid when bleeding the lines this time, usually just use Yamaha dot 4 right off my local dealer shelf.

    the brakes feel solid, lifts the back of the bike up off the ground at times. And the lever does not continue back to the bar.. but when i come in from a session/race the wheel spins 1 or 2 rotations at most. Then later, the wheel is a little more free. Could it just be hot rotors and pads? just never noticed that before..

    My brake lines are 2 individual lines from the longer banjo bolt (not the 1 into 2 style).
     
  2. walladm

    walladm #147

    How long has it been since the calipers were rebuilt? Sounds like there might just be some stubborn dirt down in the dust seal. It doesn't take much to cause them not to retract like new.

    I'll actually take one caliper off at a time off the fork, remove pads and give the lever a pump or two to push everything out slightly for cleaning. If you have a piston sticking a little, the other pistons will move first and give you an idea where the problem is.

    Hope that helps!
    -Daniel
     
  3. RM Racing

    RM Racing Tool user

    Try a good cleaning with Simple Green and water. Remove the pads, get a good brush, clean the calipers, and rinse with water. We usually do this every day at the track.
     
  4. Boman Forklift

    Boman Forklift Well-Known Member

    Looks like I've been falling down on the maintenance side a bit. I haven't been doing that nearly this often, thank you for mentioning how often you do that.
     
  5. doubleapex

    doubleapex Well-Known Member

    This!

    When new pads are installed we usually push the dirty pistons back up against the seals. The dirt provides a little stiction (is this a real word?) when the pistons try to retract or float along against the rotor.

    I usually use a soft tooth brush and spin the pistons to get all around them. I actually bought a pair of pliers just for spinning the pistons, but if you have strong farmer's hands you should be able to spin them by hand.

    What mechanism allows fluid to seep back from the master cyl to the reservoir? Is it possible this passage is a bit restricted?
     
  6. MELK-MAN

    MELK-MAN The Dude abides...

    i will try some simple green/water. Have that stuff around all the time for washin dirt bikes. I clean the pistons pretty regular but with brake cleaner and the tooth brush.. maybe not doing it as often or thoroughly as i should.

    The calipers on this bike are original, never had new seals. But, i have 2 bikes so duty is split. fluid gets changed every 6 months or less. Have been using the same EBC epfa pads since 2007 too (not SAME pads.. lol.. just same compound).
     
  7. DaveB

    DaveB Just Riding Around

    It could be possible depending on how aggressive the brake cleaner you are using that the seals have hardened up a little adding to stiction. Some brake cleaner is really bad on seals.
     
  8. MELK-MAN

    MELK-MAN The Dude abides...

    could be, but this issue seems to have cropped up all of a sudden. the wheels are off these bike a few times a race weekend. And it was just this past weekend after changing fluid to a different type than i had used for a long time, that it seems as if they were dragging a little more than we noticed ever before. Oddly, the other bike got the same treatment and doesn't seem to have this issue. Same master cyl, same lines, same calipers, pads, etc.
     
  9. motorbykemike

    motorbykemike beer snob

    what rick said

    but , you may have a tiny bit of air in the system that expands when hot
     
  10. DaveB

    DaveB Just Riding Around

    I agree, just tossing out ideas. Like you I'm sure I would be focusing on the fluid as well. While in theory all DOT4 fluids "should" be 100% compatible it might make sense to clean/rebuild the system anyway since the costs of seals, etc. is still cheaper than having something not quite right in the brakes. That way you have 100% confidence everything is right.
     
  11. racepro171

    racepro171 to finish first, first you must finish!

    take the dust seal out also. brembo race callipers don't use them, why should we. i have had mine out for years. wheel spins like a roulette. pads do wear on an angle after 50-60%. but they are soo free.
     
  12. Yoyo

    Yoyo Well-Known Member

    The brake cleaner is bad on seals.

    Use simple green as mentioned, then blow dry the calipers.
    Put a drop or two of brake fluid between the piston and caliper body then push the pistons back in.
     
  13. MELK-MAN

    MELK-MAN The Dude abides...

    ah, good idea on the brake fluid "lube" on the seals.
     
  14. MELK-MAN

    MELK-MAN The Dude abides...

    but does anyone think a master cylinder can not allow fluid back fast enough, when it otherwise works perfect ? it has good power, won't come back to the bar if you hold it, etc.
     
  15. XACT-Man

    XACT-Man Not that fast....

    I just replaced the seals in my GSXR calipers and it made a world of difference.

    If you are not having issues with the feel of the lever pulling in, it doesn't come all the way back to the bar and it doesn't feel spongy I would assess that the only other problem would be air in your line(s).


    If I'm reading this correctly you have two of the same bike, if you are really concerned, swap the masters on each bike and you will find out if the master is causing problems.
     
  16. RM Racing

    RM Racing Tool user

    Correct by Fred, an expert on brakes. Brake dust is abrasive and can create huge amounts of friction. Watch any top pro race team after a session and I guarantee you will see them cleaning front brakes - with water or Simple Green only. Brake cleaner is great, but repeated use is hard on rubber and plastic components - it takes the paint off some parts - too harsh.
     
  17. MELK-MAN

    MELK-MAN The Dude abides...

    got it. more cleaning, more often is in order.. and will lay off the brake clean.


    pretty sure any air in the lines, would give a spongy lever. Air compresses, fluid won't. For sure though on swapping master cyl to see if that is the culprit.
     
  18. Vinny337

    Vinny337 Vin is in...Beastmode!

    Melk-Man,
    Just curious how you made out with the swap…I'm having that same issue with my GSXR.
     
  19. Vinny337

    Vinny337 Vin is in...Beastmode!

    Melk-Man,
    Just curious how you made out with the swap…I'm having that same issue with my GSXR.
     
  20. Yoyo

    Yoyo Well-Known Member

    I have heard stories of -2 lines being an issue with Carbon Carbon brakes for that reason.
    (the ferrule restricted the flow)
     

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