Rear Derailer Adjustment Problem

Discussion in 'Cycling Equipment' started by Bob Grabowski, May 20, 2003.

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  1. My apologies for asking so basic a question, but this group has really been helpful to me in the
    past and please forgive me for not knowing the correct terminology. For the past 1 1/2 years I've
    been riding a Trek 1200 Road bike, graduating from a mountain bike before then. It has the Shimano
    Tiagra shifters. Recently, the rear derailer has been acting up. It is reluctant, at times, to move
    the chain onto the next smaller rear chainring. If I shift once, it doesn't move. If I shift twice,
    it moves two chainrings. I know I just need to adjust the cable tension, but I"m not sure where or
    how. Can someone help? I can call my Local Bike Shop tomorrow, but I'd like to go for a ride early
    in the morning before they open.

    Thanks,

    Bob
     
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  2. Wiscottsin

    Wiscottsin Guest

    "Bob Grabowski" <[email protected]> wrote in message
    news:[email protected]...
    > My apologies for asking so basic a question, but this group has really been helpful to me in the
    > past and please forgive me for not knowing the correct terminology. For the past 1 1/2 years I've
    > been riding a Trek 1200 Road bike, graduating from a mountain bike before then. It has the Shimano
    > Tiagra shifters. Recently, the rear derailer has been acting up. It is reluctant, at times, to
    > move the chain onto the next smaller rear chainring. If I shift once, it doesn't move. If I shift
    > twice, it moves two chainrings. I know I just need to adjust the cable tension, but I"m not sure
    > where or how. Can someone help? I can call my Local Bike Shop tomorrow, but I'd like to go for a
    > ride early in the morning before they open.
    >
    > Thanks,
    >
    >

    If it is not upshifting properly, the cable adjustment would theoretically be too tight ( not
    allowing the Der. to go all the way down to the next smaller cog ). If it was a cable tension issue,
    the solution would be to screw the barrel adjuster in ( clockwise ) to release some tension.

    But more likely it is a cable friction issue. On downshifting, you have the mechanical movement of
    the lever to "push" the chain up on to the next larger cog. But in upshifting, you are relying on
    the spring tension of the derailleur to pull the chain back down to the next smaller cog. If your
    derailleur cable becomes dirty or bent ( which most do over time ) the friction doesn't allow the
    der. to travel the full range of motion - regarding in a faulty shift.

    Try cleaning and lightly lubing the cable, or replacing the cable and the housing.
     
  3. Bob Grabowski wrote:
    > My apologies for asking so basic a question, but this group has really been helpful to me in the
    > past and please forgive me for not knowing the correct terminology. For the past 1 1/2 years I've
    > been riding a Trek 1200 Road bike, graduating from a mountain bike before then. It has the Shimano
    > Tiagra shifters. Recently, the rear derailer has been acting up. It is reluctant, at times, to
    > move the chain onto the next smaller rear chainring. If I shift once, it doesn't move. If I shift
    > twice, it moves two chainrings. I know I just need to adjust the cable tension, but I"m not sure
    > where or how. Can someone help? I can call my Local Bike Shop tomorrow, but I'd like to go for a
    > ride early in the morning before they open.

    It is unlikely that the adjustment went out by itself. Most likely, the rear derailer has gotten
    whacked and the hanger on the rear dropout is bent inward. If so, the proper fix is to straighten
    the bent hanger.

    As a temporary palliative, you can re-adjust the cable, by turning the adjusting barrel
    counter-clockwise. This adjusting barrel is located where the final loop of cable housing ends at
    the derailer itself.

    There is a danger to this, though. If the hanger is bent badly enough, it's possible for the
    derailer to overshift and go into the spokes. This can turn a minor problem into a disaster.

    See my article on Derailer Adjustment: http://sheldonbrown.com/derailer-adjustment

    Sheldon "Straighten The Hanger" Brown
    +-------------------------------------------------------------+
    | "...It is somewhat of a rude awakening for many of these | parents to find that America is facing
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    | music and its evil | influence on the young people of today... That it has a | demoralizing
    | effect upon the human brain has been | demonstrated by many scientists." |
    | - Ladies Home Journal, 1921 |
    +-------------------------------------------------------------+ Harris Cyclery, West Newton,
    Massachusetts Phone 617-244-9772 FAX 617-244-1041 http://harriscyclery.com Hard-to-find parts
    shipped Worldwide http://captainbike.com http://sheldonbrown.com
     
  4. Sorry, I meant clockwise

    Sheldon "Insert Nickname Here" Brown
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    shipped Worldwide http://captainbike.com http://sheldonbrown.com
     
  5. A Muzi

    A Muzi Guest

    "Bob Grabowski" <[email protected]> wrote in message
    news:[email protected]...
    > My apologies for asking so basic a question, but this group has really been helpful to me in the
    > past and please forgive me for not knowing the correct terminology. For the past 1 1/2 years I've
    > been riding a Trek 1200 Road bike, graduating from a mountain bike before then. It has the Shimano
    > Tiagra shifters. Recently, the rear derailer has been acting up. It is reluctant, at times, to
    > move the chain onto the next smaller rear chainring. If I shift once, it doesn't move. If I shift
    > twice, it moves two chainrings. I know I just need to adjust the cable tension, but I"m not sure
    > where or how. Can someone help? I can call my Local Bike Shop tomorrow, but I'd like to go for a
    > ride early in the morning before they open.

    Rear changer technique: Shift to high gear. Get your head behind the changer and sight the inside
    edge of the cage against the chainrings. Should be parallel. (If it isn't, correct that now rather
    than adjusting a bent derailleur.) Ensure the cable is loose or disconnect it. Shift the changer
    with your thumb up a couple of cogs and let it fall back to high gear. Does it return smartly? Can
    you get it to shift too far out past the high gear? Tighten or loosen the high gear adjusting screw
    if needed until it returns briskly to high gear and no further. Now shift with your thumb all the
    way to low gear. Hard. Ensure you cannot make the changer go past low gear. Adjust the low gear
    screw as needed until you can always achieve low gear and no farther. Try that in the low front if
    you have a wide range crank. Ensure the casings are gently curved and not binding anywhere and that
    the wire moves smoothly in it. Trim any damaged ends and oil the wire. Oil or grease the anchor bolt
    threads and the cable adjuster threads. Turn the adjuster all the way tight and then back a turn or
    two. Now connect the cable. Shift one click. Your changer should shift one gear lower. If it does
    not quite make one shift, your cable is too loose. If it is too tight you will either overshoot the
    second cog or it won't return to high smartly. Once you get a proper shift from the first click.
    look straight down or from behind and turn the adjuster such that the derailleur's roller is
    centered on the second cog. You can often do this by ear. Unless something is very much awry you are
    finished. A cursory check of the other gears should confirm that.
    --
    Andrew Muzi http://www.yellowjersey.org Open every day since 1 April 1971
     
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