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  1. #1
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    UPDATE: From 160 to 185mm rotor = bad vibration ?

    I've been running Avid BB7's with 160mm rotors. I recently bought a used 185mm roundagon rotor off ebay, which appears to be in great condition. I installed it today. Now when I use the front brake I get a bad vibration. Looking down at the axle it appears that the fork is actually flexing forwards and backwards. The flexing seems to be worse when I am seated as opposed to standing with some weight on the handlebars. I also played around for like an hour with adjusting the brake.

    The fork is a Fox Float F29. I checked and the headset is fine, hub and wheel is tight. Rotor is bolted on tight. I tried mounting the brake caliper with and without extra washers, no difference.

    I read the numerous posts on this but could not find a clear answer to my main question which is: assuming I can live with the vibration =

    WILL IT HARM MY FORK?


    ALSo, Is the vibration caused by the mismatched wear in my pads and the used 185mm rotor?

    Is it caused by the extra flex of the 185 rotor? It seems to be much flexier than the 160.

    Will the vibration get better go away as the pads and rotor bed in together? I have a Shimano 180mm rotor layin around- should I try it?
    Last edited by dragbike; 09-13-2009 at 06:48 AM.

  2. #2
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    Quote Originally Posted by dragbike
    I've been running Avid BB7's with 160mm rotors. I recently bought a used 185mm roundagon rotor off ebay, which appears to be in great condition. I installed it today. Now when I use the front brake I get a bad vibration. Looking down at the axle it appears that the fork is actually flexing forwards and backwards. The flexing seems to be worse when I am seated as opposed to standing with some weight on the handlebars. I also played around for like an hour with adjusting the brake.

    The fork is a Fox Float F29. I checked and the headset is fine, hub and wheel is tight. Rotor is bolted on tight. I tried mounting the brake caliper with and without extra washers, no difference.

    I read the numerous posts on this but could not find a clear answer to my main question which is: assuming I can live with the vibration =

    WILL IT HARM MY FORK?


    ALSo, Is the vibration caused by the mismatched wear in my pads and the used 185mm rotor?

    Is it caused by the extra flex of the 185 rotor? It seems to be much flexier than the 160.

    Will the vibration get better go away as the pads and rotor bed in together? I have a Shimano 180mm rotor layin around- should I try it?
    Try sanding the rotor and pads . Pads may be catching on distorted vent holes ??? Vibration is not good on any component - cheaper to buy a new rotor on ebay than fork, HS etc.

  3. #3
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    So I put on a used 180mm Shimano Rotor from my other bike. The vibration dissappeared! WTF is wrong with the 185mm Avid rotor. It looks fine. No warpage. Only difference I can see is that its much easier to flex side to side.

    Seriously, what is it about the Avid rotor that was causing the vibration?

  4. #4
    Former Bike Wrench
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    Roundagon rotors suck...many of the issues from Avid brakes seem to be fixed by simply replacing this rotor.

    You can use a 180mm rotor, best if you use a 160mm rear adapter up front so the pads get full contact on the Rotor.

  5. #5
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    I removed the one set of the Avid washers on the mounting bolts and replaced by one lock washer. it removed the approx 2mm gap and i now have full pad contact and the brake works awesomely. pissed off about the Avid. Wonder if the ebayer I bought it from was having the same problem. i'll save it until the time comes to replace my pads to see if it performs better with the new pads. i'll also try it on my other bike for the hell of it

  6. #6
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    I was having the same problem, I had recently bought new bb7s and was breaking them in on a sid fork and didn't notice any moving back and forth of the the fork leg. But then I switched forks and noticed the fork leg move back and forth, so I did the whole readjustment deal and haven't noticed it since.

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