Help with front derailer

[John90]

I was changing gear yesterday on the front derailer of my MTB when the cranks seized up momentarily - I think the chain got caught somehow. Back pedalling freed it up easily enough but ever since when I'm on the middle ring and the third smallest cog on the back, (my default acceleration and hill gear) the chain rubs against the front derailer cage. This is clearly a bad thing. All other ratios seem to be OK, the cage does not appear to be bent and the derailer seems to be in line. I tried the adjuster screws but without any improvement. So I'm riding on the big ring all the time now and doing all the gear changes with the rear derailer.

I checked Sheldon Brown's site but he doesn't really have any relevant solutions, although he does discuss the problem. Anyone know a good web page that deals with this?

Supplementary, possibly related, question - I generally only change gear on the front cogs and leave the back one on the same cog all the time. Is this inadvisable?

Thanks folks.

 

[Godders1]

You shouldn't need to touch the limit screws if it's been working OK previously. Cable tension is the most likely candidate.

http://www.parktool.com/blog/repair-help/front-derailleur-adjustments (see the "adjusting indexing" bit)

 

[HLaB]

The adjuster screws only limit the extent that the derailleur moves and stops the chain moving off the small and visa versa big rings and once set up correctly shouldn't need moved, as above the most likely the cables but the angle and height of the cage (also linked to above) may need adjusted but again if it worked before that won't need done which again points to the cables (cleaning, lubing or maybe replacing) or the mech that may need the same treatment.
I would say you are better to use the range of your cassette at the back (but avoiding the extremes, big front, big back or small front small back). Depending on the terrain I like to cruise in the middle ring at the front (although I often use the big ring but thats me) and use the cassette at the back to finesse and keep the big ring (at the front) for faster downhills and the small ring (at the front) for steep hills. I also find making shifts at the back aswell as being closer spaced and better for you are more reliable and I often tend to stay in one chainring.

 

[cycleruk]

i agree most likey cable tension. Thats happened to me before, the chain gets stuck and you try to free it off, eventually it frees off only to find the sprocket is now bent DOH!. This is something to look at if the cable tension and derailer is ok.

 

[John90]

Thanks for the advice. Much appreciated.