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  1. #1
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    External Bottom Bracket bearing trouble

    So I was mucking around with my chainline, shifting spacers and I noticed one of my bottom bracket bearings doesn't spin very well. The drive side bearing spins just fine (eg when testing it with my finger) but the non-drive side has a lot more resistance. Thinking there was nothing I could do about it but get a new bearing to go in there, I took the bearing out. When the bearing was out it span freely and smoothly, meaning that the actual bearing was not the problem. Anyone got any suggestions about what the problem could be?

    What would cause the bearing not to spin freely when installed in the BB cup?

    In case it matters, I have a Bontrager branded crank (probably OEM) that I think is a re branding of a Truvativ GXP crank ...

  2. #2
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    The SRAM GXP system relies on the non-drive bearing being loaded, it will always feel a little rough without the cranks installed.

  3. #3
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    It could also be the seal on the dust cap dragging against the cup lip.

  4. #4
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    Good information on the non-drive side, I was always puzzled why that side felt a bit rough.

    In the winter, about once a month, I will remove the rubber seal from the bearings (I use a hat-pin) and add some grease. The external seals are good design on the GXP, I'm not getting any water into the bearings (i.e., no rust colored grease). Be gentle when removing the rubber seal on the bearing, do not puncture the rubber, or bend the seal. It will easily fit back into place using your fingernails to seat it.

  5. #5
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    Quote Originally Posted by mtnbiker72
    The SRAM GXP system relies on the non-drive bearing being loaded, it will always feel a little rough without the cranks installed.
    Ok thanks, that would be it. Is there a way to know how much force to apply when installing the bearing? As in, is it possible to preload it too much?

    It is not the dustcover because it is rough when felt by finger.

  6. #6
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    Quote Originally Posted by maelgwn
    Ok thanks, that would be it. Is there a way to know how much force to apply when installing the bearing? As in, is it possible to preload it too much?
    If your torqued to specification, it will work just fine.

    http://www.sram.com/_media/pdf/truva.../TM_MY09_E.pdf

  7. #7
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    Quote Originally Posted by mtnbiker72
    If your torqued to specification, it will work just fine.

    http://www.sram.com/_media/pdf/truva.../TM_MY09_E.pdf
    Ok, I actually removed the bearing from the bottom bracket cup, and re-installed it when I discovered it wasn't the problem. Not quite what is expected you would do from the manual ... but it sounds like I needn't worry as it feels smooth when all installed.

    Thanks

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