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I am really at a loss of words to describe my problem, so apologies in advance for the poor choice of words in the title.

Basically I have this component at the rear wheel (which I think is called rear derailleur):

and how far it is from the spokes of the wheel is controlled by the springs(?). The trouble I have (as it seems) is that this component is too "loose" causing the chain to not be able to catch on to the component's "wheel" properly.

Compare:

Not pressed:

Pressed in:

And notice how in the former case, the chain doesn't lie flush with the "component"'s metal wheel. So that when I cycle the pedals, the chain always unhooks and causes a jam.

Is there any screw etc. that I can adjust to keep the component "pressed in", presumably something to do with the spring..

  • Is there significant play anywhere in the rear derailleur? It should follow a diagonal path across the cassette, and while some play is normal, too much could be contributing to bad shifting too. – Criggie Dec 15 '18 at 7:58
  • Have you ever crashed the bike or dropped the bike on its right hand side? Another common problem is when the hanger gets bent or twisted, or just loose. – Criggie Dec 15 '18 at 7:59
  • Just to make sure: the position of the derailleur is controlled by the cable and the spring is there just to move the derailleur to the opposite direction of cable pulling. – ojs Dec 15 '18 at 12:49
  • @Criggie I'm not sure what "play" means, but there's a fair amount of side-to-side wiggle of the derailleur. and Yes the bike fell 2 days ago, but I can't remember which side it was. – ksgj1 Dec 15 '18 at 14:26
  • @ojs thanks for pointing me towards the cable. – ksgj1 Dec 15 '18 at 15:17
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Yes, that is the rear derailleur. FYI there is a Terminology Index on this site that provides all component names.

It seems the problem you are having is that the derailleur is not lining up with each of the rear sprockets, so the chain is not running on them properly.

Most modern derailleur systems are indexed, that is the shifter lever has discrete clicks that correspond to each sprocket. What has probably happened on your bike is that the cable has stretched or loosened so that the derailleur does not sit directly over a sprocket at each position.

The derailleur or shifter cable usually has a barrel adjuster that can shorten of lengthen the cable to adjust the dearilleur position. In your case the cable likely needs to be detached from the derailleur and the effective length reset.

There are several online guides that detail how to adjust derailleurs. This one from Park Tool is probably one of the best ones - https://www.parktool.com/blog/repair-help/rear-derailleur-adjustment.

  • And your local bike shop should be able to just tune the rear derailleur for the OP for just about 20 eurodollarpounds. – RoboKaren Dec 15 '18 at 6:10

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