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  1. #1
    Brant-C.
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    Bontrager Select Cranks-XT FD; shifting rubbing problems...

    I just setup a new bike with Bontrager Select crankset and XT front derailleur bottom/top pull; I'm using the bottom pull for the bike frame.

    My problem is that it looks like the middle chainring is bigger than a shimano middle chainring and the front derailleur hits it when trying to get to the big ring. I can shift between granny and middle ring no problem.

    Do I need to get a shimano crank (XT m760 is what I would get)?

    Can I just replace the middle chainring and go with what I have?

    Also, this crank uses ISIS and it rubs when hammering in the middle chainring. Any bottom brackets that are stiffer?

    I have 2006 XTR on my other bike and it has no rubbing/shifting problems of any kind.

    What can I adjust or do to make this thing smooth?

    Anyway, thanks for any help/advise!

    Brant
    I just like riding my mountain bike.

  2. #2
    mtbr member
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    A couple of things to check....

    first is the tooth count for all three rings. If you are using the standard M 760 derialleur the max tooth count for small ring is 22T, minimum for the middle is 12T and max for the big ring is 44T. Standard mtb chainrings usually are set up as 22, 32, 44T. If you have a bigger middle ring, say 36T it could cause a problem. Replace it with a 32 and you should be okay. Stay within the max for the small and big rings and it should work fine.

    Second, check your derailleur height. Put the derailleur in the middle ring and then check the distance between the bottom edge of the derailleur cage and the teeth of the big ring. There should be a 2 to 3mm gap between them. You can get away with 4mm if needed, but it may cause the chain to rub the bottom of the cage when in the small ring in combination with the smaller cogs in the rear. If the gap is less than 2 to 3mm raise the clamp height of the derailleur until it is. If it's too low the front derailleur well could make contact with the middle ring.

    And finally, check your chain line. Shift to the middle ring up front and the middle cog in the rear. Observe the chain from the rear of the bike. The chain should make a straight line with little or no deflection of the links where the chain engages the teeth of the chain ring or the cog on the cassette. If you are seeing noticeable deflection then you have a chain line issue. Not as likely to be causing your problem as too high of a tooth count or incorrect clamp height, but it could be a contributing factor. Go back through the instructions for your BB and make sure that you've installed it correctly for the width of your frames bottom bracket housing. Most ISIS BB's are adjustable for 73mm or 68mm housing widths. If you don't get the spacers right it can cause issues. If you can't get it right with the supplied spacers then a longer or shorter BB spindle may be in order.

    Just shooting in the dark here as I don't have your bike in front of me to look at.

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

  3. #3
    Brant-C.
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    thanks squash...great stuff.

    i'll check the tooth count on the chainrings. i did measure a shimano crank chainring on my other bike and it's smaller than the bontrager chainring; so chainring size are probly the culprit.
    I just like riding my mountain bike.

  4. #4
    Brant-C.
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    my chainrings are: 28-38-48

    anyone know where i can get 22-32-44 rings for a bontrager select crank?

    thanks,

    brant
    I just like riding my mountain bike.

  5. #5
    mtbr member
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    If it's the standard...

    4 arm crank set you should be able to replace them with any 104/64mm BCD rings. It's a perfect oportunity to upgrade. Bonty rings are not known for being the most durable. The two best sets that I've ever owned for performance and durability are Race Face and Black Spire. Black Spire rings are a bit more expensive though. I'd go Race Face for overall bang for your buck. I've got a set that I've had on for two seasons with no appreciable signs of wear, and my son has a set that he's been using for almost 5 years and their still going strong. With regular drive train maintenance and chain replacement when required they'll last a long time. Price Point has the top of the line Team ring set in black for about $65, in 4 bolt 104/64 BCD that should fit your crank.

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

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