Begin Front Derailleur Adjustment With Limit Screws
To begin front derailleur adjustment, Identify the two screws that limit the movement of the front derailleur, they may be labelled ‘L’ and ‘H’ or ‘LOW’ and ‘HIGH’. If they aren’t labelled check the manufacturers service information on-line, or use trial-and-error to discover which does what. The purpose of these screws is to let the chain move across all chain-rings and no further.
Set The Low Limit
Unclamp or dismount the cable. Turn the pedals forward. If the chain rubs on the inner plate of the derailleur cage turn the low limit screw anti-clockwise to allow the spring to move the cage left until the interference is gone. Otherwise screw in the low limit screw to move the cage right until the chain brushes it, then go back a quarter turn to silence the rub.
Connect The Cable
Select the lowest gear in the shifter and close down any barrel adjusters on the cable run. These may be where the cable exits from the shifter, at a stop on the frame, or just mounted in-line on the cable. Remount or reclamp the cable. The cable should be neither lose nor tight but passive between the shifter and derailleur.
Stress The Cable
If the cable is new pull on any exposed length of inner cable to compress the ferrules and outer-cable into position. If there is no exposed length of cable you can do this by pedalling and shifting onto a larger chain-ring. Unclamp the cable and take up any slack that results from this stress test.
Select The Highest Gear
Pedal and use the shifter for the rear derailleur to select the highest gear – the smallest cog wheel – on the rear hub. If the bike has three chain-rings make another shift onto the biggest chain-ring. You may need to tighten the cable with the barrel adjuster while pedalling to enable the chain to move. If the bike only has two chain-rings it’s already there.
Set The High Limit on the Front Derailleur
Turn the pedals forward. If the chain rubs on the outer plate of the derailleur cage turn the high limit screw anti-clockwise to allow the cable to move the cage right until the interference is gone. Otherwise screw in the high limit screw to push the cage right until the chain brushes it, then go back a quarter turn to silence the rub.
Pedal hard and shift brutally to check the chain can’t be thrown off. If it falls off to the left tighten the the ‘L’ screw a quarter turn and check again. If it falls off to the right tighten the ‘R’ screw a quarter turn and check again.