Bike shifter problems?

Question

My bike has been acting up lately... it's a 21 speed, (3 and 7 gears)

I cannot shift into 3rd and 1st,

3 on the big gear and 1st on the small.

Every time I try to shift to 3,1 the chain comes right off the dérailleur and it takes me forever to get it back on.... I missed school today because of it.

what should I do to fix the thing? on my old bike (same speeds) I could shift to 3,1 no problem...

HELP!

Answer 1

the derialeur just needs some adjusting. just watch this video and you should get it after playing around for a bit. also check that its not bent. if it is its going to end up pushing the chain off.

http://www.youtube.com/watch?v=SPhcOskjs...

Answer 2

assuming you are using the correct gear numbers front 3=litle ring and back 1=big ring.....bikes are not meant to be shifted into these gear you can seriously damage or break your chain rings and chain 3 in the front should be no lower than 4 in the back and 2 in the front can go anywere and 1 in the front should go no higher than 4

Answer 3

There should be a s***w on your front derailleur labelled 'L' for 'Low'. This s***w limits how low the derailleur cage moves back.  It soulds like it is going too far back, thus your chain is able to slip off.

You will need to turn the s***w clockwise half a turn (at a guess) clockwise - If you put the derailleur in the "1" position, you should actually be able to see it move up a bit when you turn the s***w.

(much) more info here:

http://sheldonbrown.com/derailer-adjustm...

Answer 4

be sure its lined and straight. there should be a stop s***w to adjust.this keeps it from going to far.the rear derailer has 2 stop screws as well.move the derailer and turn the s***w.it may help to have some one hold the bike to check alignment