Originally Posted by
jccaclimber
This is my first guess. Worn rear cassette is on the list as well.
A picture and video would help.
Does it do it shifting high to low as well as low to high, or in just one direction?
It shouldn't have much effect on the actual shifting. It will make noise and create drag on the chain
The chain shouldn't touch anything between the two derailleur pulleys. Turn the pedals and watch the chain go through the derailleur. If it touches anything other than the pulleys, it is routed incorrectly.
This is a pic of my older XT derailleur chain routing.
