changing a front derailleur

Discussion in 'General Cycling' started by Adam Lea, Sep 16, 2011.

  1. Adam Lea

    Adam Lea Guest

    One of my neighbours has been having problems with her bike, and it
    looks like the front mech has seized (she can't shift gear at all). I
    have a spare mech from my mountain bike (her bike was a triple as well)
    so was thinking of using this to replace her old mech if it is indeed
    dead. How straightforward is it to replace a front mech and what
    compatibility issues do I need to think about? I know about outer ring
    size, is width of crank axle a potential issue as well?
     
    Adam Lea, Sep 16, 2011
    #1
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  2. Adam Lea

    Paul - xxx Guest

    Hardest bit, I think, is making sure the cable runs and pull are the
    same, there are so many variations .. then tube clamp/boss fitting and
    position on the tube.

    If they're identical derailleurs, from identically equipped bikes, then
    it's easy, if there's a difference they can be a nightmare, often
    resulting in a poorly setup unit that can't engage the full range of
    gears.

    The throw of the chain guide is mostly not an issue at all, unless
    you're swapping, say, a road oriented derailleur for an mtb based
    derailleur fitting.!
     
    Paul - xxx, Sep 16, 2011
    #2
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  3. If her front mech has seized, taking it off and cleaning it has a very
    good chance of resolving the problem (if you haven't looked yourself the
    problem could even be in the cable rather than the mech). If it has
    taken a bang, though, perhaps not.

    Otherwise, as you've guessed, lateral reach matters. Maybe indexing too.
    But it's worth trying it out.

    Brendan
     
    Brendan Halpin, Sep 16, 2011
    #3
  4. Adam Lea

    Mark Guest

    You need to get the derialleur matched to the tooth difference in your
    chainrings.
    --
    (\__/) M.
    (='.'=) Due to the amount of spam posted via googlegroups and
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    Mark, Sep 16, 2011
    #4
  5. Adam Lea

    Rob Morley Guest

    I doubt that it is - much more likely a cable or lever issue, and if
    the mech is seized you can probably free it up.
    If it needs replacing note whether it's top or bottom pull, top or
    bottom swing, chainring size, chain width (no. of freewheel
    sprockets). Apart from the pull you may get away with varying the
    others but it's best to keep them the same.
     
    Rob Morley, Sep 16, 2011
    #5
  6. Adam Lea

    thirty-six Guest

    Use penetrating oii. The original specified mechanism is likely a
    better choice and they usually outlive all other parts.
     
    thirty-six, Sep 16, 2011
    #6
  7. Adam Lea

    Adam Lea Guest

    I don't think it is the cable, as the cable was slack and twisting the
    grip shifter took up the slack smoothly until it pulled the wire tight
    then it wouldn't move further.

    If it is seized, what would you recommend as a lubricant (after
    cleaning) to try and free it i.e. something that will soak through to
    the innards?
     
    Adam Lea, Sep 16, 2011
    #7
  8. Adam Lea

    Rob Morley Guest

    If you pull the exposed cable away from the frame and click through
    the gears you can feel the lever acting on it. With the cable slack
    at the lever, pull it hard (protect your fingers with a rag) and you
    might get some movement from the mech.

    Forgot to mention - a classic reason for the front mech to stop working
    is someone fitting a U lock bracket and trapping the cable.
    Any light spray lube like WD40. You should be able to free the cage
    with just a little brute force - fingers behind cage, thumbs on seat
    tube and push/pull. Then a drop of oil when you're done.
     
    Rob Morley, Sep 17, 2011
    #8
  9. Adam Lea

    Phil W Lee Guest

    Paraffin or diesel, if you can't find any plus-gas, for soaking it in
    to free it off, then dry it and put a drop of motor oil on each pivot
    point to stop it happening again.
     
    Phil W Lee, Sep 17, 2011
    #9
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