If the lever was moved the wrong amount, the deailer might shift the chain too far, or not shift at all.
It might also shift to the desired gear, but not line up quite right with the sprocket, so the chain would run rough and noisy.
Deraillers almost never "wear out", at most they need new jockey wheels. What does get worn out is the rear cogs or cassette. Generally getting good performance out of canti's has more to do with how well you set them up rather than the exact model you use.
Loose derailleur bolts might not cause a shifter to malfunction, but a loose attachment can affect gear changes.He earned a Bachelor of Arts degree in liberal studies from UC Riverside in 2004.Bicycle shifters allow you to control the gears on a multispeed bicycle.I have an aluminum frame bicycle (mountain bike, 21-speed) that I purchased some time in the late 90s, it's marked "Skykomish Eureka" (though I can't find any evidence that such a brand and model ever existed), and it is currently outfitted with Shimano 300LX components.I believe that the rear shifter is giving up the ghost, as sometimes the lower (up) handle will go all the way back without "catching" whatever it's supposed to be catching in order to shift the gears.