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  1. #1
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    Avid bb5 replacement problems

    Hope you all can help me out with this. I am trying to upgrade the cheap disc brakes on the bike I bought for a commuter. The bb5s bolt on easily, but the bottom of the front mount it so close to the rotor it rubs slightly and both mount are out of parallel with the rotors. (They tip backward at a slight angle so that the discs deform when the brakes are applied).

    The bike is an 2000 KHS soft-tail, with a marzocchi bomber fork. Is there specialty mounts or shims required? Is machining often necessary to make these work? Has anyone else ever run into this problem?

  2. #2
    Never trust a fart
    Reputation: frdfandc's Avatar
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    What is happening is there is a layer of uneven paint that is keeping your brackets from mounting flush. Just take a small fine file and remove the paint till you see metal. Cover the bare metal with clear nail polish and then you can mount up your calipers/brackets.

  3. #3
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    ?? I will take a closer look, but they were more like 1/8" out both directions, more than I would think paint could cause.

  4. #4
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    Is the disc mount on the fork IS mount or post mount?

    If it is IS mount, then it means that the post mount BB5 calliper has to be used with the adapter bracket. This is desirable because the calliper (not the adapter) can be adjusted parallel to the rotor - just loosen the two bolts, hold the calliper to the desired angle and retighten.

    You will have noticed that the convex and concave spacers on the adapter bracket are exactly the same type as used on v-brake pads - this is what allows the adjustment.

    If the rotor is touching the adapter (not the calliper since it can be adjusted to clear it), then do as frdfandc suggests or add a 2mm (approx) washer to each side of the wheel axle. Alternatively, you could just add one washer and redish the wheel.

    Another thing to look out for is the length of the bolts - make sure that they don't portrude out from the adapter bracket onto the rotor.

  5. #5
    Never trust a fart
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    If the caliper and brake pads are not square with the rotor, it is due to the uneven layer of paint on the mounts. It is common to see this on low level disc brake systems with out some sort of (to use the Avid phrase) "CPS system" Caliper Positioning system.

    The CPS kit used conical washers to help position the caliper square to the rotor surface.

  6. #6
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    Quote Originally Posted by fox_boy
    Hope you all can help me out with this. I am trying to upgrade the cheap disc brakes on the bike I bought for a commuter. The bb5s bolt on easily, but the bottom of the front mount it so close to the rotor it rubs slightly and both mount are out of parallel with the rotors. (They tip backward at a slight angle so that the discs deform when the brakes are applied).

    The bike is an 2000 KHS soft-tail, with a marzocchi bomber fork. Is there specialty mounts or shims required? Is machining often necessary to make these work? Has anyone else ever run into this problem?
    Sounds like your disc tabs need to be faced. This is not uncommon with some frames. I agree that there may be more going on here than just paint. The adapter should clear the rotor by a good 1 to 3mm in most cases, and it should be vertical when tightened down. I would try filing the paint off of the mounting tabs and see if that works, it is possible that a sloppy paint jockey may have gotten that much excess on the tabs. However if you still are having problems after that then there needs to be some metal removed from the tabs. I'd take the bike into a good shop and have the disc mounting tabs faced. There are specific tools and methods that need to be used to keep the tabs flat and concentric to one another or you'll end up with worse problems than you started with.

    Good Dirt
    "I do whatever my Rice Cripsies tell me to!"

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