Help with derailleur (?)

This Park Tool page has links to tutorials on derailleurs and shifters. In fact, you should book mark the Park Tool site as it has tutorials on virtually anything you could ever need to do to a bike.

+ 1 on the Park Tools website. It sounds as if you might have experienced cable stretch. It happens in 30 - 90 days after a new cable has been installed. Unscrew the barrel adjuster on your left shifter a quarter turn at a time until the derailleur cage is centered over the large chain ring when the left shifter is in the number 3 position. If this doesn't solve your problem, you might have to slightly unscrew your H limit screw on the derailleur body to center the cage over the large chain ring, but this adjustment should not need to be done umless someone has been messing with the adjustment screw to begin with.

Oh I wish I had seen this post earlier. 🙂 I went to the Park Tools page and couldn't follow it well enough (they would mention part names, but I had no idea what they were), so I found some YouTube videos on it. Then I basically started from scratch on adjusting the derailleur. I moved the cage up and down and adjusted the angle. I tried the H and L screws but couldn't tell what they do. Now I can't even shift into the biggest chain ring. Initially I had a suspicion that the barrel adjustment should do something useful, because I saw the guy at my bike shop play with it, but I adjusted it all the way both ways and it didn't fix the problem. However, perhaps I should have tried adjusting it in smaller steps.

I'm thinking I better just suck it up and pay to get it fixed now. It was rideable before even though it would make a scraping sound, but now I have to use my fingers to get it on the biggest chain ring, which is where I like to ride mostly.

Thanks for the help!

komi said:

I tried the H and L screws but couldn't tell what they do. Now I can't even shift into the biggest chain ring. Initially I had a suspicion that the barrel adjustment should do something useful, because I saw the guy at my bike shop play with it, but I adjusted it all the way both ways and it didn't fix the problem. However, perhaps I should have tried adjusting it in smaller steps.

I'm thinking I better just suck it up and pay to get it fixed now. It was rideable before even though it would make a scraping sound, but now I have to use my fingers to get it on the biggest chain ring, which is where I like to ride mostly.

FYI. On Shimano TOP PULL front derailleurs, the 'H' set screw which is closer to the seat tube controls the outwards swing of the front derailleur's cage by limiting the rocker arm's motion ...

Try this:
[INDENT]Back the H screw out so that about 2mm of the threaded portion is showing ...

Take the chain off of the chainring(s) ...

Hook your LEFT THUMB in the top of the cage (and/or your RIGHT INDEX FINGER on the outside of the inner plate if the spring is too stiff for you to move with only your thumb) and manually pull the cage away from the frame ... and then, look down at the position of the chainring relative to the derailleur's cages ...
[/INDENT]Initially, you want to outer chainring to be about 1/3rd away from the outer plate & 2/3rds away from the inner plate.

Put the chain back on.

Test.
[INDENT]If you don't have a workstand and/or if you can't find someone to hold the rear wheel off the ground while you slowly turn the crank & test the shifter, then take the bike outside with screwdriver in hand ...
[/INDENT]Then, in an area where you don't have to worry about traffic/pedestrians, slowly pedal the bike & attempt to shift ...

If the chain doesn't move all the way onto the outer chainring, then stop the bike, turn the 'H' screw counter-clockwise by a 1/4 turn ...

Test.

Repeat ...

If the chain comes off on the outside of the crank, then turn the 'H' screw clockwise.

Test.

Repeat until the chain no longer comes off on the outside of the chainring.

IF the chain won't stay after you have successfully adjusted the front derailluer THEN there may be a problem with the shifter (i.e., it's worn out) and it may need to be replaced.