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  1. #1
    dude
    Reputation: joeyjoedotorg's Avatar
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    Does my HFX-9 HD need to be rebuilt?

    So I'm having some trouble aligning my calipers on the rotor. When I took them off, I noticed that my calipers have the notorious "dominant piston" problem. After doing some searching here, I cleaned up the pistons as best I could by holding the "dominant" piston back and pumping the brakes to push out the weaker piston.

    It seems like wherever the weaker piston is, it doesn't stay pressed out like the other piston.

    I thought that there might be an air-bubble in the system too, so I went ahead and did a bleed, but to no avail.

    Do I need to drop $20 and get a complete rebuild kit? Has anyone done this? How difficult is it? Thanks in advance for any info.

  2. #2
    Meh.
    Reputation: XSL_WiLL's Avatar
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    Eh, even if you rebuild it, you'll likely still have the same problem. Do the best that you can with it. Lube the piston with DOT fluid and work it in and out.

  3. #3
    dude
    Reputation: joeyjoedotorg's Avatar
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    did that already

    So rebuilding the calipers won't help me out much?

    I'm thinking of using some shims to move the caliper over so that it centers a bit easier (towards the weaker piston) so that it's basically a hayes so1e.

  4. #4
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    it may be a spacing issue

    I was having the same problem, what I did was add a couple washers to space it out a little more and it worked well.

    I hope that helps.

  5. #5
    dude
    Reputation: joeyjoedotorg's Avatar
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    I will try that out tonight and see how it works... I imagine it'll work.

  6. #6
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    How old is the brake? Most of the manufacturers recommend replacing the caliper pistons every couple years as they and the caliper piston seals do get worn. I've changed them before and the differemce is noticeably and markedly improved.
    You are not what you own.

  7. #7
    dude
    Reputation: joeyjoedotorg's Avatar
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    this is off an 05 Jamis Komodo; the bike and the brakes have hardly been ridden though. 'still on the first set of pads.

    I used some spacers between the fork's tabs and the adapter and it seems to have done the trick for me. no (significant) rubbing on the rotors anymore.

  8. #8
    SLX
    SLX is offline
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    I had some new Hayes DH once. And got the dominant piston problem too. They seem to brake in and work better after some use. Your going to have to reposition them again after they brake in. Mine are still working!
    Leave no bolt untuned!

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