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Thread: Sticking brake piston

  1. #1
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    Sticking brake piston

    I have 4 pot caliper with a sticking piston. I can spin the front wheel but you can hear it rubbing and the rotation is not as free/fast as I believe it should be. The pads are wearing faster under this particular piston than the others. I have replaced all the seals and meticulously cleaned everything and put it back together. It still did not retract as much as the other pots (you can see it moving back, just not as much as the other 3). I pulled it all apart again. Measured the pistons, all measure the same and then replaced them in different positions to see if it made any difference. It didn't. Pulled the whole lot apart again in case I missed something like a speck of dirt but nothing. Anyone have a suggestion, am thinking the rebate that houses the seal may be a thou or 2 shallower than the others.

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    14th July 2006 - 21:39
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    What's the bike, year and brake (brand).

    Too much drag is never nice
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  3. #3
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    Tokico, 2007 GSXR 750

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    Have you checked to see if the disc is true ... ??
    Sweat wipes off. Road-rash doesn't.

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    A warped disc kicks away the pads, His appears to be constantly dragging only on one pad. if it warping it will only drag in one position.
    Sorry i suggest taking the caliper apart again and degunking it.
    If one piston doesn't retract fully its normally surrounded with crud that prevents it going back.
    Is the piston itself free of nicks etc? the caliper itself?



    Kinky is using a feather. Perverted is using the whole chicken

  6. #6
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    The discs are running true, no problem there. I pulled the whole thing apart after work ,cleaned out the seals and grooves again but no improvement. Its doing my head in.

  7. #7
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    Have you checked the piston is round with a accurate caliper?

  8. #8
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    No, I havnt checked for round but I have put each of the other pistons into the same pot and they all do the same thing. Am thinking I need to find a way to measure the I.D of the seal groove to see if it is smaller than the other pots of the same size.

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    Beg / borrow / steal ... another set of calipers and see if there is improvement ...
    Sweat wipes off. Road-rash doesn't.

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    Quote Originally Posted by Premature Accelerato View Post
    No, I havnt checked for round but I have put each of the other pistons into the same pot and they all do the same thing. Am thinking I need to find a way to measure the I.D of the seal groove to see if it is smaller than the other pots of the same size.
    Is there enough meat on the disc to reface it/them ... without going under minimum disc thickness ... ??
    Sweat wipes off. Road-rash doesn't.

  11. #11
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    Quote Originally Posted by Premature Accelerato View Post
    No, I havnt checked for round but I have put each of the other pistons into the same pot and they all do the same thing. Am thinking I need to find a way to measure the I.D of the seal groove to see if it is smaller than the other pots of the same size.
    how did you clean out the groove?

  12. #12
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    If the same caliper bore is the problem with different pistons, I'd look at the bore.
    It's easy enough to mark the bore putting pistons in dry or crooked.

    Edit - Pull the seal and see how free the piston is in the bore. Might have to get a pro to give it a light hone.
    Reason is a tool - remember where you left it..... The late, great, John Clarke

  13. #13
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    cleaning out the groove it the had bit, i use a dentists hook tool to get right to the edges and ensure there's no crytalised bits in there, that's the worst area and will put extra pressure on the seal

  14. #14
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    Quote Originally Posted by jellywrestler View Post
    cleaning out the groove it the had bit, i use a dentists hook tool to get right to the edges and ensure there's no crytalised bits in there, that's the worst area and will put extra pressure on the seal
    Cleaned it with the curved end of my trusty old scrubber. I have just pulled it apart again and put the piston in the pot without any seals. It slides in and our easily. I then put the oil seal in by itself and the piston works the same as the others. I then put the dust seal in and the bloody things tightens up to buggery. So I would guess that perhaps the seal is slightly too big or the seal is a little over size. All the extra cleaning at least gets me a 1 1\2 turn of the wheel when I give it a spin. Enough ya reckon?

  15. #15
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    Quote Originally Posted by Premature Accelerato View Post
    Cleaned it with the curved end of my trusty old scrubber. I have just pulled it apart again and put the piston in the pot without any seals. It slides in and our easily. I then put the oil seal in by itself and the piston works the same as the others. I then put the dust seal in and the bloody things tightens up to buggery. So I would guess that perhaps the seal is slightly too big or the seal is a little over size. All the extra cleaning at least gets me a 1 1\2 turn of the wheel when I give it a spin. Enough ya reckon?
    so if you suspect the seal a differnt size measure it with a vernia
    or why not put that seal in another hole and try and chase the fault,
    a curved end of a trusty old scrubber, sounds like a dildo of a chick i knew in featherston, commonly known as metahamfeatherston.
    seriuosly what is that tool? as said i use a hooked dentist tool, lightly but you can feel the shit and feel it dissapear

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