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  1. #1
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    Hayes 9 HFX HD - Piston Out Too Far?

    I am currently using Hayes 9 HFX HD's, and accidentally pulled the rear brake leaver when the rear wheel was off. My piston in the Hayes 9's rear brake are now pushed in. I have tried to push them back with a spanner, however they spring back as soon as I touch the leaver. My problem is they now rub on the disk, the piston is too far out.



    The picture shows that the right hand piston is about 1mm out from running flush with the side, any ideas how to get it flush with the caliper again?

    - Matt.

  2. #2
    Nightriding rules SuperModerator
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    just push it back..... with the pads installed, use a clean screwdriver (remove any grease from it with alcohol, just to make sure) and wiggle the screwdriver between the pads to make the pistons move back...

  3. #3
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    I did this, crisillo, so I can then get the wheel on then. Though, as soon as I pull the rear brake once the pads push back to nearly clamping the disk. Meaning when I ride the rear brake is always slightly on.

    Is there any way to make them permanently stay flush, as they originally were?

  4. #4
    Nightriding rules SuperModerator
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    well..usually that is the job of the pad spring or magnet depending on the brake (haven't played much with HFXs)

    also consider that the pistons will stay out to compensate for wear, so they might not need to be completely flush, unless the pads are new, but they should retract enough in order not to be braking all the time...

    is the pad contacting the rotor all the time or only certain spots?

    also make sure that the caliper is well centered.... one piston coming out a bit more could also mean that the caliper was shifted to one side...

  5. #5
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    Before I took off my rear wheel to repair a puncture the pads had about 1mm clearance on either side of the rotor and they ran perfectly centered.

    Though, when the wheel was off, I accidentally pressed the rear leaver and they closed in. I pushed the pads back with a screwdriver to get the wheel in, however now there is about 0.1mm clearance either side of the rotor now the wheel is back in. The pads are now sort of 'defaulted' to only retract that far, they don't move back to have 1mm clearance anymore.

    Is there some sort of reservoir of hydraulic liquid to compensate for the pad wear? I am thinking (as I have never taken apart hydraulic brake systems) that the reservoir pumped more fluid into my lines causing the pads to close in more? I am unsure how the hydraulic system works, but maybe if I bleed a bit of fluid out the pads will retract?

    edit: The pads are just about contacting the disk all the way around, in some parts rubbing.

  6. #6
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    Shimming under pressure

    Back the pads as far as possible. stick any thing flat and solid between the pads. Squeeze the lever hard a few times. They should be reseated now.
    Over time brake dust, gunk, mud seeps in behind your pads and probaly will form a crust on the piston making it harder to retract all the way. Do this when your pads start to rub about 1/2 half thru new pads. and make sure your caliper blocks are lined up.

    Good luck.

  7. #7
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    Well once they go out they never seem to want to push back in.

    I find that the only solution is to push the pistons back in with the bleed cap open. A bit of fluid will probably come out and you need to stop it getting on the paint.

  8. #8
    ride hard take risks
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    Quote Originally Posted by ellhow
    Well once they go out they never seem to want to push back in.

    I find that the only solution is to push the pistons back in with the bleed cap open. A bit of fluid will probably come out and you need to stop it getting on the paint.
    You can put a section of hose on the nipple after you snug it put a rag or paper towel under the hose durring removal to catch the excess fluid.
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