From my experience and reading various posts in soc media there are two challenging issues: operation of front derailleur and the the disc brakes
1. Front derailleur - the difficulty of fd shifting to the largest chain. I experienced this myself. Several actions are suggested:
1. Check and oil the pivot. Dirt and astray parts could jam the mechanism
2. Check the cables: the outer and the inner cable. You can clean and oil the cables. The dirt and crud could jam the shifter action
3. The limit screw. The outer limit screw, the hi limit screw could be loosened by 3/4 to 1 turn (or more as the case may need it)
4. The barrel adjuster. A turn or two can make the fd shift nicely
2. The disc brake. That is why the rim brakes (the V brake) are simpler to maintain. The most common
complain is squealing brake. Or failing brake
1. Failing brake could be caused by:
1. Worn out pads - replace when the metal back is almost exposed
2. Worn cable - replace
No more mineral oil - add
Air in the system - bleed the brake
2. Noisy brake
1. Caliper not centered. Center the caliper by sight - lossen the mounting bolt and and try
tightening usual visual sight
2. Score in the disc - try to sand, and or replace
3. Glazed brake pads - clean with detergent, alcohol and/or sand paper
But sometimes these may not work and the noise/squeaal reappear
Try and try until the sound disappear
