rear caliper trouble
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Thread: rear caliper trouble

  1. #1
    coco bongo Array Lyzic's Avatar
    Join Date
    May 2003
    pedalling like a madman

    rear caliper trouble

    Please help me, I need to figure out what's wrong here

    So I went for a ride, rear brake seized on me. I applied it once and about 2 miles later the drag was so much I stopped, the disk was smoking and it was hot hot hot.

    Let it cool down, it backed off a bit so I was able to ride it home.

    I took the back caliper off to see what the problem was.

    I think my pads are screwed

    I turn them over and see this, notice the ring of oil (?) or brake fluid on one

    And the piston in the caliper has oil on it too, there was more, all around but I wiped some off when I touched it

    So what do you all think?

    If I press the brake pedal, the piston moves out a little, but doesn't retract at all. Should it? (this is when it's not installed on the bike.)

    It is super stiff, by hand I cannot move the piston at all. Is this normal, or is it seized? How much should it move? I can move it with a clamp but not very easily

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  3. #2
    Hangin' with my gnomies Array whillis's Avatar
    Join Date
    Mar 2006
    in the van, man
    a two wheel love machine
    When you press the pedal the piston will move out, but it wont go back in on it's own. You should be able to press it back in by hand, even if it seems stiff. Could be that you have a bad seal or some water got in and corroded the housing. If it was me I'd pull it apart and have it checked.
    It's all fun and games until someone loses an eye, then it's a scavenger hunt.

  4. #3
    Unregistered User Array bombermanx's Avatar
    Join Date
    Sep 2004
    ZX6R M.E.
    brake fluid probably boiled over and leaked through the piston seal? It's a single piston caliper, besides the piston, the slider pins could be seized too, which can prevent the pads from moving away from the rotor after the brakes are released.

    Normally, the piston moves back only a tiny bit to clear the pads from the rotor, I don't think it's easily noticable just by looking at it. And it normally takes a bit of effort to push the piston back.

    BTW, Make sure the brake fluid doesn't touch any painted surfaces because it eats paint for snacks.

    pads and rotors are shot due to overheating, caliper maybe rebuildable.

  5. #4
    Registered User Array slowzuki's Avatar
    Join Date
    Apr 2005
    In your bitch
    Your mama...(late model)
    did you do any work to the rear brake leading up to this? Or has anyone? Was the rear wheel taken off lately?

    If so check and make sure the caliper was re installed properly and was fit properly to the swing-arm...if not then flush your brake fluid and clean all the brake dust (every bit) off the piston and lube the sliders and get some new pads and take for a test ride. If when you apply the rear brake you feel pulsing in the padal --replace your rear rotor: if not then don't.
    Last edited by slowzuki; 06-09-2006 at 10:45 PM.
    “……If a chick sits on your face and you can't hear the stereo anymore...she's too fat! --The Machinist.

  6. #5
    Moderator Array TeeTee's Avatar
    Join Date
    Feb 2002
    Out to pasture in the 'Wack
    04 Kawi Z1000,
    Quote Originally Posted by Lyzic
    ....It is super stiff, by hand I cannot move the piston at all......
    It's toast. You need to rebuild the caliper with new seals and possibly a new piston.

    You will also need to carefully check the rotor for warping or stress cracks. Use a long straight edge to check for warping or cupping. To check for cracks sand the dark color off the swept surface and clean it well. Then use a strong magnifying glass to look for cracks in the surface. Any signs of cracks would be cause for replacement. Any warping or cupping the same. But don't confuse the usual hollow from wear as this.

    The stiffness can come from a number of causes. Old seals that have been heated too often grab the pistons too hard. Old fluid that has gotten water in it and/or gelled will prevent the system moving. Old fluid that absorded lots of water and promoted corrosion inside may have lead to a stuck piston as well.

    When it comes apart look the piston over carefully for signs of corrosion pitting. Try cleaning it with something like a Scotchbrite pad or some chrome polish. If it's got any pitting after these two light duty cleanings then you need a new piston.

    To get the piston out just hang the caliper in a little bucket and pump the brake pedal until the piston spits out long with the brake fluid. Look the fluid over carefully for signs of age. Lumpy jelly like blobs and a cloudy look are signs of advanced abuse. Super dark fluid is less so but still bad.

    Clean the inside of the caliper with special care to cleaning out the seal grooves and then install the new seals (and piston) using clean brake fluid to lube them all. Refill and bleed the system and you're good to go.
    A backyard mechanic without a service manual is just like a hooker without a lamp pole.... they are both in the dark.

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