Front Brake conundrum

Discussion in 'Maintenance' started by Fingers202, Sep 7, 2020.

  1. Fingers202

    Fingers202 New Member

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    Evening, I have a braking issue on a ZX6r, 2008, I'm working on.

    Wheels were swapped out for same model new wheels and discs, on rebuilding and taking for a test ride the front braked bound on bringing the bike to a virtual standstill.

    Both calipers have been stripped cleaned and move freely with low air pressure; ran the bike again and the same happened.

    Master cylinder and all brake lines stripped, cleaned / blown through, took it for a run slightly better until the same occurred after a longer distance, same result though.

    At a loss as I have never experienced this on any bike previously, the rider has no idea of this was occurring previously.

    Any suggestions on what to check / do next is appreciated.
     
  2. Muffking

    Muffking God Like

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    Assumings it's a twin disc, is the wheel definitely the same as the old one and why was it changed.
    Could be worth loosening the calliper bolts to see if this releases the pads off the disc proving an offset problem.
     
  3. dern

    dern Active Member

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    Once they're bound on and the brakes release does loosening the bleed nipple on either calliper produce fluid under pressure? That might give you a clue where to look next.

    Have you got after market levers and are they adjusted so there's no pressure on the master cylinder when you fully release the brake lever?
     
  4. Fingers202

    Fingers202 New Member

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    Picked up a pair of near new wheels and discs, from same model bike. Exactly the same wheels and discs. Standard lever and oem pads.

    Dust seals removed, pistons continue to move freely.

    Last run found the same happened, however stop very sharply (stoppie) the wheel doesn't bind as much, which makes me think its the master cylinder. Gentle braking seemed to allow the pressure to build.

    Releasing pressure at bleed nipple helped, which I think all points to the master cylinder.
     
  5. CharlieR85

    CharlieR85 Senior Member

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    If its bad enough to slow the bike to a stand still and you're sure the pistons in the calipers move back freely then it has to be a fault with the master cylinder I would say.

    It could be the piston not retracting in the master cylinder. Did you re-grease the piston in the MC when you stripped it? Was it moving in the bore freely? Could be worth buying a piston re-build kit for the MC.
     
  6. Fingers202

    Fingers202 New Member

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    Thanks folks, further examination found that the calipers were [email protected]$ked. Where the lower pads sit the caliper body was worn, causing the pad to 'ride up' on what was a wedge, jamming them against the disc(s). New calipers ordered and that should be that!
     
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