Bike not shifting properly

[viet_Cong]

hey i got a 21 speed MTB, my problem is that its not shifting very well in high gears

note - i got 3 crankset in front (right shifter side handle), and 7 cassette in back (left shifter on handlebar)

my problem is:

- when in in gear 2 in right shifter (front) , and try to go to gear 6 on the left shifter (back) the chains jumps and wobble around trying to shift to like 5th gear. when i go to gear 7 it wants to jump to gear 6.

- same thing happens if i go in gear 3 in right shifter (front) , it takes like 7-8 rotate to get from gear 2 to 3 in front (is that normal?), but same thing happens when i try to shift the left shifter from gear 6-7.

- it kinda hard to explain but that the best i can describe it.

[Bill]

Hi viet,
Check your chain wear by viewing this.... http://bikeride.com/chain-wear/ also there are links at the top of this thread that will help ya out.

[viet_Cong]

thanks, oh yeah forgot to tell, i replaced my chain(chain snapped in half so i had to get a new one) . but it happened before and after i replaced the chain. do you think its the cassette or derailer?

[marcdominic]

Viet,

Most likely both the cassette and the front chainset. However you say it also happens on the largest chainring (Hmm...). In my experience replacing the chain also requires replacing the cassette and the middle chainring because they've worn together and the middle chainring is the most used. Maybe your outer (largest) chainring requires replacing too if you use it a lot...?

[EDIT] Does this not happen on the smallest chainring?

[DaveM]

Worn cassette and front chainrings usually won't affect shifting too much though. At least not when you're putting light load on the pedals.

First things I'd check are just the normal shifter adjustments and make sure your rear derailleur isn't a little bent. That can happen when a chain breaks. But check all the adjustments before you start buying a lot of new parts.

[viet_Cong]

oh ok, ill post some picture of my bike tomorrow or soon,