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  1. #1
    I don't huck.
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    How true does a rotor have to be?

    A little story. I put BB7s on the SS and soon enough ended up with a nasty pulse under braking in each wheel. It was bad enough to lock the wheel if it was unweighted enough. No fun when precision braking was required.

    I tried different things, pad sanding, rotor sanding with emery cloth, the rotor seemed quite true to me...maybe a slight run out in the rear, but the front was dead on.

    Swapped to G3 Cleansweeps and new, organic pads. Much smoother overall, but the pulse remains. HUH? So I figured it had to be one of two things...the rotors were still out of true, the hubs were not faced true, or there was some vertical hop to the rotors.

    I made sure the rotors were as true as possible. I can barely see light between the pads and rotors and there is some contact as I spin, but wow...that is getting down to such fine adjustments that I am surprised I can even feel what I am seeing.

    I wonder if the BB7s, since they have that one, fixed pad, if they are more sensitive to rotor trueness (trueness???)

    Very odd. I bedded the pads in carefully down a 8 mile downhill on pavement. They pulsed at the beginning and at the end...no difference. By now after about 6 or 8 caliper alignments, I am pretty satisfied they are square to the rotor, but if not, I would not know how to do it a better way.

    Puzzled.
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    West Coast writer for twentynineinches.com

  2. #2
    trail addict
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    Rotors are so flimsy that being a little out of true shouldn't make them pulse (too much). Sounds more like possible grease/oil contamination to me.

    Clean everything with rubbing alcohol and a clean rag. If the problem persists, clean again and put on new pads.
    You better just go ahead and drop that seatpost down to the reflector... the trail gets pretty rough down there.

  3. #3
    I don't huck.
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    That is what I was thinking about the rotors as well. They should deflect that much under braking. Well, this is new pads and rotors, all cleaned and the problem followed. Hmmm. I guess I could clean them again...and again.

    So far, Avid has been a mixed bag for me all together.
    Blog Ramblings
    West Coast writer for twentynineinches.com

  4. #4
    mtbr member
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    1- How far down on the rotor arms are the pads hitting.

    2 - I find it unlikely out of 2 different rotors, but I had a rotor that the thickness varied by .004" and produced a strong pulse that matches what you are describing. You would have to measure them with a micrometer to know.

  5. #5
    I don't huck.
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    They are down onto the arms, but it looks like they are also right at the top of the rotor brake track as well.
    Blog Ramblings
    West Coast writer for twentynineinches.com

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