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Thread: Rear brake help

  1. #1

    Default Rear brake help

    Trying to bleed the rear brake on my 92 1200 sportster and when i crack the bleeder i get constant fluid but the piston in the caliper gets to a certain point and won't go any further. Anybody have any ideas why that would happen? The manual i have wasn't much of a help on the subject.

  2. #2

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    Might need more info.
    The piston won't travel out far enough?
    Maybe the master cylinder is not moving enough fluid for any number of reasons. Maybe there is corrosion in the caliper and the piston is getting jammed with it, or getting cocked sideways?
    The caliper bracket could be bent and uneven loading of the piston causes a jam?
    I've seen a perfectly good looking caliper that would work on the bench but anytime real pressure was applied it would stick solid.
    Byperfectly good looking I mean taken apart, cleaned thoroughly, and no corrosion! New caliper solved that one.

  3. #3
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    Quote Originally Posted by DRare View Post
    Trying to bleed the rear brake on my 92 1200 sportster and when i crack the bleeder i get constant fluid but the piston in the caliper gets to a certain point and won't go any further. Anybody have any ideas why that would happen? The manual i have wasn't much of a help on the subject.
    Why are you bleeding the brakes????? Was it giving you problems or did you change the pads.....

    Tell us more............

  4. #4

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    sorry, i forgot. I did a hardtail on the frame and i'm reassembling the bike now. the bike was a total pile before any of this so i'm not even 100% it worked before. Even with the caliper off of the bike the piston will only extend maybe 1/16th of an inch out and then if i try to build up more pressure to get it to move it'll just stay in that spot. if there's corrosion in the caliper is there a way to remove it without being too abrasive or do you just replace the caliper at that point?

  5. #5

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    I would call that caliper junk and get a new one. You might want to stop reliably.
    It's not like it was just working fine yesterday.
    Someone might tell you you can clean it up and it will be fine, but they aren't the guy who will be riding it.

  6. #6

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    On a related note, I've seen a guy put air into the inlet to pop out the piston while holding the caliper.
    It flew out mashing his fingers and got jammed there cockedat an angle because it was almost out. We pried the piston back with a pry bar to get them out!
    Same guy got his wedding ring arced between the battery and the frame...

  7. #7

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    If the master cylinder won't pump the piston out of the caliper, you have master cylinder problems.

    Jim

  8. #8

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    the master cylinder will pump it out about 1/16th. I got the caliper piston out and it there was dirt under it and the walls of the caliper that it sits in are kind of corroded. might just look into replacing it.

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    Quote Originally Posted by DRare View Post
    the master cylinder will pump it out about 1/16th. I got the caliper piston out and it there was dirt under it and the walls of the caliper that it sits in are kind of corroded. might just look into replacing it.
    Oh yea if there is trash in it that's a lot of your problem.....

    Did you replace the lines???? You know are they new??????

  10. #10

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    Yes, i made a new stainless braided brake line with new fittings. I'll look into replacing the caliper and I'll update the tread if it works. Thanks.

  11. #11

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    The master cylinder setup may still be suspect.
    The normal stroke of the master cylinder might only move the piston 1/16" or a bit more.
    The problem is that when it is fully released it should draw in more fluid from the reservoir and the next pump should move it another 1/16" or whatever it is, and so on.
    The piston should continue to move out until the reservoir is empty and the master cylinder is sucking air.
    If there is anything preventing a complete return of the master cylinder piston then it might not return far enough to open the port and gulp some more fluid.
    Check that the pedal and linkage are allowing a full return at the master. There should be slight free play at the plunger when the pedal is at rest.
    Also, I'm not sure but someone else on here will probably know this, there may be a residual pressure valve in the master cylinder and it may be malfunctioning.

  12. #12

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    actually oddly enough i decided to try to scotch brite the piston a little bit and the chamber where it sits, and then put a tad bit of brake fluid around both and it sealed right up and decided to work now. So weird. Might look into replacing the rear caliper since that's my only brake on the bike.

  13. #13
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    Quote Originally Posted by DRare View Post
    Might look into replacing the rear caliper since that's my only brake on the bike.
    Smart thinking....

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    Quote Originally Posted by Tattooo View Post
    Smart thinking....
    Last time I rode with only one brake I left tire tracks on the ceiling of a 7-11, we all gotta be young once! So I would suggest 2 brakes! But if you must have only one replace the master and caliper after you flush the lines you pumped full of sludge.
    Dusty

  15. #15
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    Quote Originally Posted by DustyDave View Post
    Last time I rode with only one brake I left tire tracks on the ceiling of a 7-11, we all gotta be young once! So I would suggest 2 brakes! But if you must have only one replace the master and caliper after you flush the lines you pumped full of sludge.
    Dusty
    LOL When I was a kid and had my first Harley I rode to Daytona with just a front single disc brake..... About a 10 hour ride..... I had just changed the bike over the winter and I didn't have the money yet to buy a rear caliper.....

    Yes Youth.... The things we will do..... LOL

  16. #16

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    I'm sure there are a lot of us older guys who rode around with only the rear mechanical brakes on old Harleys. You sure didn't wear flip flops since your feet were your back up braking system. I think if you survived it made you a better rider; you learned not to tailgate and to always be ready to dodge large solid objects like 73 Ford LTDs.

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