Left shifter on my mountain bike is not shifting, what can I do?

Question

I have a 17 in Trek mountain bike, and the left shifter (gears 1-3) is not shifting, how can I fix this problem? Thank you.

Answer 1

You'll need to be more specific about the problem. What do you mean by not shifting? Is the derailleur failing to push the chain or is the derailleur not moving at all? If the former, you will most likely need to readjust the derailleur/cable tension. If the cable haven't been changed for a long time it's possible they have stretched beyond what can be fixed by adjustments, in which case you will need to replace the cable (~$5). If so, I'd suggest you change all four cables at once as they other ones are probably in bad shape too. There are many good tutorials online for this, but I highly suggest you have a look at the excellent site http://bicycletutor.com or http://www.parktool.com/ "Repairs How-To" section. If the derailleur is not moving at all. Check that the cable isn't damaged or cut off. In the unlikely event that the cable seems in good shape and has some tension in it, you may need to get your shifter serviced or replaced. If you cannot move the shifter's levers, then the derailleur and/or cable might be stuck by some foreign debris.

Hope this helps.