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Thread: Rear brake issues... piston seized? Or not enough pressure?

  1. #1
    Member AC_Schnitzel's Avatar
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    Rear brake issues... piston seized? Or not enough pressure?

    Went to change my pads -- it took a lot of force to push the piston back in. More than what I think would be normal.

    Upon reassembly, I added new fluid and bled the line for any air that might have gotten in.

    Pressing the brake lever, the piston doesn't move outwards at all...

    Is my piston seized? Or am I somehow not maintaining pressure in the master cylinder?

  2. #2
    Senior Member 34nineteen's Avatar
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    You probably still have air in the piston. Hydraulic force through those braided brake lines should easily push the cylinder OUT.

    Did you clean off the piston when you had it apart? Most every XB I’ve owned has sticky pistons, especially up front.

  3. #3
    Member AC_Schnitzel's Avatar
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    Quote Originally Posted by 34nineteen View Post
    You probably still have air in the piston. Hydraulic force through those braided brake lines should easily push the cylinder OUT.

    Did you clean off the piston when you had it apart? Most every XB I’ve owned has sticky pistons, especially up front.
    Nah -- I just pushed it back in. Now the pedal isn't pushing the piston back out.

    I don't have a compressor or grease gun -- how else could I get it out?

  4. #4
    Senior Member 34nineteen's Avatar
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    Is the lever going to the bar? If yes, then you have an air bubble. Keep bleeding.

    If not, then something is stuck.
    You could always take it to a bicycle shop and ask them to blow it out with compressed air. Usually they are easier with that sort of stuff than an auto/mc garage. Make sure to stuff a shop rag in there the pads go to catch the piston and make sure it doesn’t damage anything when it comes flying out at high speed.

    Or I will sell you mine for $20 + shipping

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    Member AC_Schnitzel's Avatar
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    St Paul HD doesn't have a rebuild kit for the rear caliper... Anybody know an equivalent part number for the Nissin assembly?

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    One other option but it will cost more is a hidden rear caliper set up. Also, get yourself a syringe, maybe a turkey baster and push fluid from the caliper to the master cylinder. Once you have pressure, you can do it the old fashioned way using long strokes while bleeding at first, then use short fast strokes until satisfied. While the bike sits overnight, put a zip ty around the bar and the lever nice and tight. In the morning it should be like new again. Presently, if it's not leaking it's probably ok.
    Last edited by outthere; 04-05-2020 at 07:58 PM.

  7. #7
    Senior Member 34nineteen's Avatar
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    Quote Originally Posted by AC_Schnitzel View Post
    St Paul HD doesn't have a rebuild kit for the rear caliper... Anybody know an equivalent part number for the Nissin assembly?
    How were you planning on rebuilding it, if you can’t remove the piston?

  8. #8
    Senior Member 34nineteen's Avatar
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    Quote Originally Posted by AC_Schnitzel View Post
    St Paul HD doesn't have a rebuild kit for the rear caliper... Anybody know an equivalent part number for the Nissin assembly?
    You probably should take your bike to a shop. This is all over your head.

    https://st-paul-harley-davidson-buel...2010-xb-models

  9. #9
    Member AC_Schnitzel's Avatar
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    Quote Originally Posted by 34nineteen View Post
    You probably should take your bike to a shop. This is all over your head.

    https://st-paul-harley-davidson-buel...2010-xb-models
    That is a brand new caliper assembly... I'm not trying to spend $90 when a few new seals and piston is <$20

  10. #10
    Member AC_Schnitzel's Avatar
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    Quote Originally Posted by 34nineteen View Post
    How were you planning on rebuilding it, if you can’t remove the piston?
    My neighbor has a compressor -- might ask him if I can use it to push the piston out.

    I'm also going to rebuild my rear MC first and see if that fixes the issue.



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