Troubleshooting
Problem -Solution
Mech won't shift from big to middle -Turn barrel adjuster clockwise
Mech won't shift from middle to small -Check low limit screw. If that's OK, turn barrel . . .. adjuster clockwise
Mech won't shift from small to middle -Turn barrel adjuster anticlockwise
Mech rubs on small chainring -Wind low limit out slightly
Chain falls off when shifting to small ring -Wind low limit in slightly
Chain falls off when shifting to big ring -Wind high limit in slightly
Chain won't go into big ring -Wind barrel adjuster and/or high limit screw
Chain rubs in big ring -Turn high limit out slightly. If no joy, check cage alignment
General erratic shifting performance -Clean, lube or replace cable. Check mech for wear - if there's a lot of slop in it, replace.