Mountain Bike Shifting Problem
 

Hey guys,

My bike has a shifting problem. While I'm riding it, I can not get it to shift into 3rd gear (The biggest in the front). However, when I get off the bike and try to figure out the problem, it shifts into 3rd gear just fine. Does anyone know what would prevent it from shifting while I was riding it, but not when I am turning the pedal with my hand? All of the other gears work fine.

Any and all help is appreciated!

For your question, far to little info is given, what sort of shifters, Gripshift / SRAM, Shimano etc do you have, how many speed etc, is the hanger bent, if it's removable it is bolted up tight?

For a start, look at Park Tools how too guide http://www.parktool.com/blog/repair-...illeur-systems, there are also videos on Youtube you can search for.

It's not uncommon for the shifting to vary slightly when you're on the bike, as opposed to on a stand.

There is likely a barrel adjuster for the front derailer somewhere along the cable path. Turn it counter-clockwise 1/4 turn to provide a bit more tension in the cable, then get on the bike and try again. If things get slightly better, keep adjusting it until it works.

Keep track of how many turns you use so that you can get back to the original position, if necessary.

You are easing off your pedaling force while you are trying to shift, right? Shifting to larger chain rings while there is tension on the chain is problematic since the mechanism needs to lift the chain up. Downshifting is easier since all the chain has to do is drop down.

If the bike has rear suspension, the chain comes in to the derailer at a different height depending on how much the suspension is compressed.

Also, from the same cause, the cable may tug or give slack from suspension movement on certain designs.

If the bottom bracket is loose, pedaling may force the big chainring away from the chain, but only during part of the rotation. If the chainring is also bent, it could make or break the shift actually occurring.