On my MTB I am having the problem with the front shifter that it won't shift in to the top chainring without putting a ton of force in, so much that i can only shift it with my right arm, I don't have the strength in my right arm. Ages ago when I first started having this problem I sprayed WD-40 on it but that made it so the part you move with your hand slid over the actual shifting mechanism (this is a Shimano twist shifter BTW). I figured there are three possible causes:
1. This only started after I converted from 42 teeth to 48 teeth with a SRAM front derailleur. Is this because shifters designed to work with 42 tooth cranksets can't generate enough movement to get up to a 48 ring?
2. The shifter needs taking apart and servicing
3. The shifter is just buggered and needs replacing
If any one has got any ideas they would be much appreciated.
Here is a picture of the shifter if that helps