Tools needed for most repair/maintenance work on rear derailleurs:
- 5mm Allen key or Allen key in multi-tool
- Screwdriver
- Needle-nose pliers
- Cable cutters
Most rear derailleurs are indexed, which means that for every click of the shifter, either up or down, the derailleur will shift the chain from one cog to the next.
Occasionally, you may find that the chain does not quite move onto the next cog when you make a single shift, or else it skips a cog in an overshift. In either case, the rear derailleur needs adjusting. You will also need to follow the steps in this sequence whenever you fit a new cable.
To ensure that the rear derailleur works faultlessly, pay particular attention to its jockey pulleys because this is where oil and dirt can accumulate. Degrease and scrub them every time you clean your bike. Whenever you lubricate the jockey pulleys or the rear derailleur pivots, make sure you wipe off any excess oil.
Parts of a rear derailleur:
- Derailleur pivot
- Cable-fixing clamp
- Jockey cage
- Barrel adjuster
- Jockey pulley
Adjusting a rear derailleur
1.Shift the chain onto the biggest chainring and smallest cog, then undo the cable-fixing clamp so that the cable hangs free.
- Check the cable and fit a new one if it shows any sign of fraying.
- Screw the barrel adjuster in or out, until it is at half of its range.
2. Use the high adjuster (usually marked “H”) to line up the jockey pulleys with the smallest cog.
- Once you have lined them up, rotate the pedals forward while adjusting the “H” adjuster until the chain runs smoothly.
- Pull the cable downward through the cable- fixing clamp and re-clamp it.
3. Shift onto the smallest chainring and largest cog.
- Push the rear derailleur with your fingers toward the spokes. If it moves beyond the largest cog, screw in the low adjuster (marked “L”) until the derailleur stops at the largest cog.
- Turn the pedals to see if the chain runs smoothly. If it does not, adjust the “L” in or out.
4. Shift back to the smallest cog, then shift upward through each gear. If the rear derailleur does not shift all the way onto the next-biggest cog, screw out the barrel adjuster until it does. If the derailleur overshifts and skips a cog, screw in the barrel adjuster until it stops.
5. Prevent the jockey pulleys from making contact with the bigger cogs by screwing in the adjuster that butts onto the rear derailleur hanger on the frame dropout. Remember to make this adjustment if you fit a block or cassette with bigger cogs than usual.
