Rear derailer problems

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

  1. Mark

    Mark Guest

    Hi,
    I've just fitted a new chain and am having real problems getting the
    rear derailer to change. Instead of properly changing the chain will
    move sideways off the top jockey wheel and end up "in-between" gears.
    No matter how I adjust the cable tension it fails to change properly.

    It's a low-mid range shimano on a 7 speed cassette.

    And ideas? It's worked faultlessly up until now.
    --
    (\__/) M.
    (='.'=) Due to the amount of spam posted via googlegroups and
    (")_(") their inaction to the problem. I am blocking some articles
    posted from there. If you wish your postings to be seen by
    everyone you will need use a different method of posting.
     
    Mark, Sep 16, 2011
    #1
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  2. Mark

    Adam Lea Guest

    Knackered jockey wheel?
     
    Adam Lea, Sep 16, 2011
    #2
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  3. Mark

    Simon Mason Guest

    It is quite common for a new chain not to mate with a worn cassette
    and will not engage with the teeth properly.
    It sounds like you may need a new cassette as well.
     
    Simon Mason, Sep 16, 2011
    #3
  4. Mark

    Mark Guest

    It looks OK. I'll try a replacement if I can get to the shop.
    --
    (\__/) M.
    (='.'=) Due to the amount of spam posted via googlegroups and
    (")_(") their inaction to the problem. I am blocking some articles
    posted from there. If you wish your postings to be seen by
    everyone you will need use a different method of posting.
     
    Mark, Sep 16, 2011
    #4
  5. Mark

    Tim Guest

    Is the chain the same length as the old one?

    Tim
     
    Tim, Sep 16, 2011
    #5
  6. Mark

    Rob Morley Guest

    Top pivot jammed (or adjuster/stop sitting wrong) so the derailleur
    body doesn't swing forward as the cage swings back?
     
    Rob Morley, Sep 16, 2011
    #6
  7. Mark

    Mark Guest

    I don't think so. The cassette is fairly new and the chain is seating
    on it fine.
    --
    (\__/) M.
    (='.'=) Due to the amount of spam posted via googlegroups and
    (")_(") their inaction to the problem. I am blocking some articles
    posted from there. If you wish your postings to be seen by
    everyone you will need use a different method of posting.
     
    Mark, Sep 16, 2011
    #7
  8. Mark

    Mark Guest

    I don't know for sure but probably. The old chain snapped and fell
    off in traffic and I couldn't find it! I used the same method as I
    usually do to fit it.
    --
    (\__/) M.
    (='.'=) Due to the amount of spam posted via googlegroups and
    (")_(") their inaction to the problem. I am blocking some articles
    posted from there. If you wish your postings to be seen by
    everyone you will need use a different method of posting.
     
    Mark, Sep 16, 2011
    #8
  9. Mark

    Phil W Lee Guest

    And (given that the problem is sideways fit) is it the same width as
    the old one?
    What is described by the OP is what I would expect if a 10s chain was
    fitted to a 7s drive train.

    Also check the B screw adjustment, as it may be that the mech is too
    far from the sprockets.
     
    Phil W Lee, Sep 16, 2011
    #9
  10. Mark

    thirty-six Guest

    There should be a minimum of four and a maximum of six free links
    between sprocket and pulley. Wheel axle position, derailleur angle
    and chain length all affect this. A new chain frequently needs mpore
    than the minimum usual distance because the chain is relatively stiff.
     
    thirty-six, Sep 16, 2011
    #10
  11. Mark

    Clive George Guest

    Hmm - my installed-to-spec derailleur and cassette has the pulley really
    quite close to the sprocket. Seems to work fine.
     
    Clive George, Sep 16, 2011
    #11
  12. Mark

    Phil Cook Guest

    Keeping the top guide pulley close to the sprockets improves changes
    because there is less chain to flex sideways.

    The spec for chain length given by the Japanese outfit beginning with an
    'S' is length on big ring and big sprocket plus two links. They suggest
    setting the B-tension adjustment so that the top guide pulley is as
    close as possible to the biggest sprocket.
     
    Phil Cook, Sep 16, 2011
    #12
  13. Mark

    Clive George Guest

    Suntour? :)
     
    Clive George, Sep 17, 2011
    #13
  14. Mark

    thirty-six Guest

    My adjustment is to the commonly used sprockets, the middle ones. I
    don't care that my derailleur has to climb on and off the biggest
    sprocket, it's a gear I use only in very rare and extreme
    circumtances. If I ever use it more than 0.5% of the time, I'll be
    looking for a triple chainset. The fact that I can select and
    deselect from the big un is enough, I want good shifting through the
    gears I use the most.
     
    thirty-six, Sep 17, 2011
    #14
  15. Mark

    thirty-six Guest

    Any closer in chain length than two inches and you will be
    unecessasarily working the top spring which will fail prematurely at a
    possibly inopportune moment. That you can, doesn't necessarily mean
    you should. A new chain with heavy grease will frequently not work
    with a closely maladjusted derailleur.
     
    thirty-six, Sep 17, 2011
    #15
  16. Mark

    thirty-six Guest

    No, it's SR Suntour these days.
     
    thirty-six, Sep 17, 2011
    #16
  17. Mark

    Rob Morley Guest

    That totally depends on the the spring/derailleur in question. Modern
    derailleurs are designed to run close to the sprockets, the springs
    are designed to handle it as is the whole system of
    chain/sprockets/jockey wheels ...
     
    Rob Morley, Sep 17, 2011
    #17
  18. Mark

    Mark Guest

    Thanks to all who replied. I took it apart and reassembled it again
    over the weekend and it's much better now. It changes fine now across
    the whole range but turning the pedals backwards causes the top run to
    go slack and moves the cage and the chain disengages from the
    cassette.

    I do note that there is only about 2 free links from the sprocket to
    the top jockey wheel so this looks the most likely culprit.

    The chain is the correct width BTW.

    --
    (\__/) M.
    (='.'=) Due to the amount of spam posted via googlegroups and
    (")_(") their inaction to the problem. I am blocking some articles
    posted from there. If you wish your postings to be seen by
    everyone you will need use a different method of posting.
     
    Mark, Sep 19, 2011
    #18
  19. Mark

    Rob Morley Guest

    Sounds like drag in the freehub.
    Unlikely - I just checked a couple of my bikes, they only have a couple
    of (half) links from jockey wheel to sprocket, and their setup is
    spot-on.
     
    Rob Morley, Sep 19, 2011
    #19
  20. Mark

    Mark Guest

    On further investigation it appears that the lower jockey wheel will
    not move. The inner side plate of the cage has a piece that curves
    inwards which is now touching the jockey wheel. I have checked that
    the jockey wheel is complete. The plate has not been bent so I cannot
    explain why this is happening.
    --
    (\__/) M.
    (='.'=) Due to the amount of spam posted via googlegroups and
    (")_(") their inaction to the problem. I am blocking some articles
    posted from there. If you wish your postings to be seen by
    everyone you will need use a different method of posting.
     
    Mark, Sep 19, 2011
    #20
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