I am attempting to change the derailleur cable on a 2004 K2 Zed Sport. It is a 26", 21 speed, city/ mountain bike with the shifters built into the handlebars. To shift, the rider twists a grip, and the bike shifts. My attempt to change the cable has gone bad - the shifter no longer makes the clicking sound indicating a shift. There is some small piece of metal in the handlebar twister that may be the source of the problem. Any ideas on how to fix this? Any videos on Youtube showing how to fix this?