New BB, chainset but new front mech doesn't work - HELP!

Discussion in 'Cycling Equipment' started by ianlew2303, Mar 7, 2013.

  1. ianlew2303

    ianlew2303 New Member

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    Hello, I have a 2009 Trek 7.3fx Hybrid. Recently I changed the BB, Front Mech, chainset and cassette because they were all a bit knackered after a few years of hard riding.

    Everything was fine until I put the front mech on. Even if I pull it as far as possible from the bike, the outer edge only ever comes parallel with the chain, and not slightly beyond it. Therefore I can't change into the top chainring. I've tried changing the end stop screw, but this doesn't make enough difference.

    Now I made sure that the new Shimano BB was exactly the same length as the old one (quite long at 122mm). Is it possible or likely that the new chainset might be a bit thicker than the old one, and so I need to get a shorter BB, rather than replicating the old one?

    The old front mech was a Shimano C102, new one is a Shimano Alivio FDM412, new chain set is Shimano FC-M411 Alivio 48/38/28T, instead of original M361.

    If anyone can help or advise I would be extremely grateful!!
     
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  2. CAMPYBOB

    CAMPYBOB Well-Known Member

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    See FD installation and setup instructions here: http://techdocs.shimano.com/techdocs/blevel.jsp?ASSORTMENT%3C%3East_id=1408474395181679&FOLDER%3C%3Efolder_id=2534374302051829&bmUID=iQjmSIH

    Assuming you can disconnect the shift cable and manually adjust the cage to achieve the outer travel to the No. 3 picture (Top Adjustment), you have a cable tension issue, low starting position issue or combination of the two.

    If the derailleur can not achieve the outermost swing position, you may have a chainline problem. If you go with a shorter BB, make sure you have clearance for the chainrings, but my guess is that if the cheap old C102 shifted, the new Alivio will throw your 3-ring setup.
     
  3. alfeng

    alfeng Well-Known Member

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    IF everything seemed to work until you put the new front derailleur on, then you can EITHER put the old front derailleur back on the bike OR figure out what you are doing wrong ...

    Of course, it would probably be beneficial if you could go through a process of elimination ...

    • if you still have the old crankset & old BB then put them together & measure the outside distance at the tips of the crankarms AND at the spindle -- compare with the same distnces on your new crankset
    • look at the inner & outer STOP SCREWS on the old front derailleur & on the new front derailleur -- again, compare

    PICTURES MAY BE BENEFICIAL.
     
  4. ianlew2303

    ianlew2303 New Member

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    I wish I had kept the old kit to reference, but just assumed that because all the new kit was compatible on the shimano tech docs site, and the new BB was the same size as the old that it would all be good.

    In the absence of the old kit am I basically reliant on getting a new BB which is shorter? The front mech won't pull out any further.

    Thanks
     
  5. alfeng

    alfeng Well-Known Member

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    Again, PICTURES WOULD BE BENEFICIAL ...

    In the absence of pictures, MEASURE the distance of the outermost chainring from the CENTER of the seat tube ... and, POST that information ...

    ALSO, measure the GAP between the inside of the ends of the crank arms and the chainstays ... and, POST that information ...

    You may indeed have the wrong length BB spindle, BTW ...

    BUT, why did you think that you would want the same 122mm length for the replacement chainset if it was a different model than the one you were replacing?!? I presume your bike's frame is aluminum ... is that right?

    Again, PICTURES WOULD BE BENEFICIAL.
     
  6. oldbobcat

    oldbobcat Well-Known Member

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    The profiles of Acera and Alivio cranks and chainrings should be pretty much identical, and your new Alivio derailleur is designed to work with these cranks with the correct spindle length.

    Measure the distance from the centerline of the seat tube to the centerline of the middle chainring and let us know what you get. It should be 50 mm.
     
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