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  1. #1
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    Problem? with Hayes HFX-9 XC

    Hello

    I have a pair of Hayes HFX-9 XC hydraulic disc brakes.
    For reference, these brakes come with a glycol based brake fluid.

    Now to my problem;
    I rode a very short distance to the store, 1,25km, pushing my front brake extra hard because I just finished cleaning it from teflon oil...
    After the third deeper descent the brakes started scratching the disc.
    Now I understand the principle of heat expansion and so on.
    MY problem is this, it's 10 degrees celsius below freezing outside!
    How could this "heat" expand the liquid enough to affect the brakes at this temperature? :S
    I doubt the caliper even reached +1 degrees, the down hill portions came at like 200m apart.

    Any clues?

  2. #2
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    Clarify please

    What does this part of your sentence mean? "because I just finished cleaning it from teflon oil..." Where was the teflon oil? In the brake?

    Randy @ Hayes
    Last edited by Randy@Hayes; 03-03-2005 at 03:50 PM.

  3. #3
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    Quote Originally Posted by Randy@Hayes
    What does this part of your sentence mean? "because I just finished cleaning it from teflon oil..." Where was the teflon oil? In the brake?

    Randy @ Hayes
    There was a single drop on the rotor itself, wich I cleaned off with some disc cleaner, the stopping power is now fine.
    The scratching has happened once before but way less, I just thought at that time because they were (are) new. Bought the bike tuesdays.

  4. #4
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    Glad to hear....

    it was on the rotor.

    Use only rubbing alcohol and a clean paper towel to clean your rotors. If your pads had gotten teflon oil on them, they need replacement. Depending on your pad material, you might have to re-bed in the pads for the braking power to return to normal.

    Cheers,
    Randy@Hayes

  5. #5
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    Quote Originally Posted by Randy@Hayes
    it was on the rotor.

    Use only rubbing alcohol and a clean paper towel to clean your rotors. If your pads had gotten teflon oil on them, they need replacement. Depending on your pad material, you might have to re-bed in the pads for the braking power to return to normal.

    Cheers,
    Randy@Hayes
    Well.. That wasn't really the problem, I've contaminated rotors and brake pads before.
    Cleaning them with success and having them return to full condition, without buying new pads.

    >>The problem is that the pads will start to scratch on the rotor after a few hard stops, as if the fluid expanded. In my country it is currently winter, and the temperature drops below -10 Celsius (14 Degrees Fahrenheit)<<

  6. #6
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    At that temperature...

    The seals don't flex like normal in the caliper and the piston slips on the seal so they might rub the disc. The square seal stiffens up and won't give optimal retraction. The brake will act normally at higher temps. Remove the pads, push the pistons back in the bores, reinstall the pads, see if that helps.

    Randy@Hayes

  7. #7
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    Randy, what's the typical clearance between the piston and the bore? Is that why pistons stick (putting aside cold temperatures for the moment), because the clearance it too tight? What's the cause of one piston moving more than the other one? I'm just trying to figure out why so many hydraulic calipers behave this way.

  8. #8
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    Quote Originally Posted by Randy@Hayes
    The seals don't flex like normal in the caliper and the piston slips on the seal so they might rub the disc. The square seal stiffens up and won't give optimal retraction. The brake will act normally at higher temps. Remove the pads, push the pistons back in the bores, reinstall the pads, see if that helps.

    Randy@Hayes
    They retract fully and normally, after a minute or so.
    And it seems to happen when they have "heated up".
    After they retract from the few hard stops, they will perform normally.

    Anyway, we'll see how they perform when summer is back.

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