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  1. #1
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    Avid Piston Questions

    Hi,

    Im having a severe issue with my Avid Ultimate rear caliper and my new scrub rotor.

    Pushed the pistons back, installed a new set of pads and new rotor. The previous pads/rotors ran perfectly drag free 100%

    This new setup just will not line up. The pad furthest from the cassette is constantly dragging the pad - no mater how many times i try to line it up...

    So my question - how far into the caliper do the pistons need to go when reseting the system ? On mine i pushed them as much as i dared but the pistons where still sticking out about .5mm i guess. Should they sit flush into the caliper body ?

  2. #2
    TNC
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    noMAD man
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    On Elixirs the piston faces still protrude a tiny bit from the caliper body when bottomed out, so I'd suspect that Juicy's do the same. I'd think both pistons should be extending out from the caliper body the same amount, so unless there's a mismatch in that amount, you probably have them pushed in as far as they'll go. Unless you use an inappropriate tool or something to push the pistons back in to the calipers, the pistons should just bottom out in the calipers. I think you'd have to do something weird to damage the pistons or the rest of the system by forcing them back in...hammers and chisels should be avoided...LOL!

    Did you measure the exact width of the new rotors with some quality calipers to see if they're slightly thicker than the OEM rotors you replaced? You may just have a slightly sticky piston. Even though you can force the piston fully back into the caliper, it may not retract enough to stop rubbing. There are some good posts on this forum that describe how to smooth up a sticky piston that are worth checking if that's your problem. Installing new pads often result in some rotor drag until the pistons loosen up on their own to match the new, thicker pads or the sticky piston is tweaked per suggestions already mentioned in other posts. Still, the first thing I'd do is insure that your new rotor is at least no thicker than your OEM rotor since it is a different brand.

  3. #3
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    Hi,

    I was running Hope Pro rotors which according to the digital caliper i used to check them (first thing i did) they are 1.6mm thick.

    The new Scrub rotors however are 1.83mm thick. That's why i reset the pistons but as far as im aware Avids stock rotors the G2/G3 are 2mm thick i belive ?

  4. #4
    TNC
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    Just for grins, I just measured four of my G3 Avid rotors and got between 1.82 and 1.94. It doesn't sound like you should be having any trouble there.

  5. #5
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    Maybe ride them a couple days and see if they get better.

  6. #6
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    My guess is the TNC is on the right track suggesting a sticky piston.

    After pushing the pistons into the caliper, the important thing is for both pads to reach the rotor at the same time. After you tighten the caliper bolts (while aligning the caliper), the pads must also retract a equal amount away from the rotor. If they don't retract the same amount every time, one will start rubbing.

    I would start by cleaning the piston sides with brake fluid and cycling them fully in and out several times.

  7. #7
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    Hi,

    So a bit of an update. I continued to bed the new rotors in, got back from doing so and the rotor is now running 90% drag free, there is a bend in it which comes over and touches the outer pad. But at least i can get the wheel spinning!

    When i initial changed the brake pads there was alot of residue in the caliper, so using some IPA i cleaned it out, got the pistons nice and clean etc. The one thing i didn't do however was relube them with DOT Fluid.

    Theres one thing i noticed last night. When i pull the brake lever the rotor gets moved towards the cassette - so could the outer piston perhaps be out too far and is contacting the rotor to quickly and also not helping with it rubbing ?

  8. #8
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    Quote Originally Posted by Tiffster
    Theres one thing i noticed last night. When i pull the brake lever the rotor gets moved towards the cassette - so could the outer piston perhaps be out too far and is contacting the rotor to quickly and also not helping with it rubbing ?
    Yes. The inner piston closest to the cassette is probably not moving as freely as the outer piston. Therefore the outer piston has to move the rotor over to the inner before braking happens.

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