Front brake doesn't seem spongy but there a lot of "free travel"

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Front brake doesn't seem spongy but there a lot of "free travel"

This is a discussion on Front brake doesn't seem spongy but there a lot of "free travel" within the ZR-7 Maintenance forums, part of the Kawasaki ZR-7 category; Hi, So i need to press brake lever like 3-4 cm before it starts to brake, if i press brakes with full force the lever ...

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  1. #1
    Newbie TadyZ's Avatar
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    Front brake doesn't seem spongy but there a lot of "free travel"

    Hi,

    So i need to press brake lever like 3-4 cm before it starts to brake, if i press brakes with full force the lever can almost touch the handle. At first i thought that the problem was hoses, so i changed them to HEL braided ones. But braking didn't change at all. Also the master cylinder seems ok, when i was bleeding the brakes after changing hoses i've noticed that it squirts brake fluid at around 2cm of lever travel. "Elastic band" method helps only for a while, i win ~1cm but after a while it goes back. Brake pads also seems good, i compared them with new ones and there is a lot of the pad left.

    What could be the problem?

  2. #2
    Obo
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    Supreme Being Obo's Avatar
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    I'd make sure your fluid is topped up in the reservoir first.
    Next if you have factory levers try adjusting the dial settings. I can't recall if the it decreases pull required if you dial them up or down.
    Next I'd check the pads for thickness (I know you said you did). If they are shot - replace them!
    It could also be an air bubble somewhere which would require more bleeding.
    Lastly if there's no leaking anywhere, and the hoses are not expanding (you said you replaced them), then my guess is the seals in the piston at the reservoir are leaking and may require a rebuild kit.

    If in doubt have them checked by a professional. They are kind of important
    2004 Kawasaki ZR-7S
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  3. #3
    Newbie TadyZ's Avatar
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    Yeah, i think i will rebuild master cylinder. All the other parts seems ok. I've also noticed that if i leave brakes on for the night in the morning there is no grip even if the lever is fully pressed(when i depress the lever and press again the brakes are back). There are no leakes, so the only thing that could be "leaking" is master cylinder.

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    Rising Star Lentz's Avatar
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    Most Kaws seem to have a bleed nipple at the lever. I always manage to forget that one and scratch my head for a while.

  6. #5
    Newbie TadyZ's Avatar
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    So, the update.

    I've done a master cylinder rebuild. The rubbers on the old one seemed good and after the rebuild and bleeding nothing much changed :/ So me and my father investigated calipers. Apart from pins being a bit sticky, everything else seemed fine (we lubricated them).

    But we have noticed that pistons travel a lot. Each piston moves ~0.5mm in and out when the lever is pressed and depressed. So the big part of lever travel is "used up" to move pistons without them creating any braking force. So that seemed to be the problem.

    Is it normal? My father said that pistons normally don't travel that much, especially when lever is depressed.

  7. #6
    Newbie TadyZ's Avatar
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    I think i've found a solution. Will try it in near future.

    Quote from reddit:
    The basic premise of the problem is that when you apply the brakes, the rubber gaskets in the caliper stretch to allow the pistons to move the pads agains the rotor and that because of this stretch, the piston is not able to slide out from the caliper. When you release the brake the rubber gaskets "grab" the pistons and pull them back into the caliper leaving a larger than normal gap between the pad and the rotor. Every time you want to apply the brakes, the pads have to close that excess gap before meeting the surface of the rotor, hence the increased lever travel before the brakes would actually engage.

    It's actually really simple to solve this problem. The "Vincenzo method" mentions removing each caliper finding something slightly thinner than your rotor, inserting it between the pads, and compressing the pads onto the slightly thinner material so that the pistons can reseat in the gaskets.

    I didn't bother with that, but what I did do was remove each caliper one by one, press the brake lever once with the caliper removed, then do a test fit of the caliper back on to the rotor. After doing this a few times with each caliper, the caliper would not slide on and off the rotor easily meaning that the pistons had reseated properly in the gaskets, and the gap between rotor and pad was very small as it should be. Now when I apply the brakes, the brakes engage within the first 25% of the lever travel and I can't squeeze the lever all the way to the grip even if I tried.

    I hope this helps someone else.
    Original post.

    Also linko to Vincenzo method.

  8. #7
    Site Elder JustAJ's Avatar
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    Sounds like you may have found your issue, but I'll throw in my 2 pennies anyway. I had a track bike that was doing this exact thing, and it turned out that the brake pads had been contaminated with fork oil. An easy test is to remove one or both of the pads and hold a torch to the braking surface for a few seconds. The flame will pull any fluids to the surface if they're contaminated. If they're not, no harm no foul, it's just a little fire.

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