Rear Derailer Adjustment Problem

[Bob Grabowski]

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

 

[Wiscottsin]

"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.

 

[Sheldon Brown]

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
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[Sheldon Brown]

Sorry, I meant clockwise

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

 

[A Muzi]

"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