What a derailleur does and why it gets misaligned
A derailleur is the mechanism that moves your chain between the different sprockets on your cassette (rear wheel) or chainrings (front crank). When it stops shifting cleanly or the chain rubs against the cage, the derailleur is usually out of alignment — not broken. Most fixes involve adjusting two small screws and the cable tension, which takes 10 to 20 minutes with basic tools.
Derailleurs drift out of alignment from normal wear: cable stretch, dirt buildup, a bump to the derailleur arm, or a chain that has worn unevenly. The good news is that you do not need to replace the part. A few small adjustments bring it back to working order.
Key Takeaways
- Most shifting problems come from cable tension that has loosened over time, which you can adjust with a barrel adjuster without removing the derailleur.
- The limit screws (marked H and L) stop the derailleur from moving too far inward or outward, and they need to be set before you adjust cable tension.
- A rear derailleur that rubs the chain or skips gears usually needs the barrel adjuster turned counterclockwise a quarter-turn at a time until shifting is clean.
- A front derailleur that struggles to shift up to the largest chainring often needs the high-limit screw loosened slightly to let the cage move farther outward.
- If the derailleur arm is visibly bent or the cable is frayed, the part may need replacement rather than adjustment.
Identify which derailleur is the problem
Shift through all the gears on both the front and rear while listening and watching. A rear derailleur problem shows up as chain rub, hesitation when shifting between sprockets, or the chain falling off the smallest or largest sprocket. A front derailleur problem appears as the chain rubbing the cage when you are on the middle or large chainring, or the chain not moving up to the big ring at all.
Check the derailleur arm itself for damage. If it is bent visibly or the mounting bolt is cracked, the derailleur will not respond to adjustment and will need to be replaced. If the cable is frayed or kinked, replace the cable before adjusting anything else. A good cable should move freely when you wiggle it by hand.
Set the limit screws on a rear derailleur
The two small screws on the back of the derailleur are labeled H (high gear) and L (low gear). These screws prevent the derailleur from moving so far that the chain falls off either end of the cassette. Set these first, before touching cable tension.
Shift to the smallest sprocket (highest gear) on the rear cassette. Look at the derailleur from behind the bike. The inner plate of the derailleur cage should be parallel to the sprocket, not angled inward or outward. If it angles inward toward the spokes, turn the H screw clockwise a quarter-turn. If it angles outward away from the sprocket, turn it counterclockwise a quarter-turn. Test and repeat until the cage is parallel.
Now shift to the largest sprocket (lowest gear). The outer plate of the cage should be parallel to that sprocket. Adjust the L screw the same way — clockwise if the cage angles outward, counterclockwise if it angles inward. Once both limit screws are set, the chain should not rub on either end of the cassette.
Adjust cable tension on the rear derailleur
Most shifting problems come from cable tension that has loosened. The barrel adjuster is a small cylindrical knob on the derailleur or the shifter where the cable enters. Turning it counterclockwise increases tension; turning it clockwise decreases tension.
Shift to the middle sprocket and pedal slowly. If the chain hesitates to move up to smaller sprockets or rubs on the sprocket below, turn the barrel adjuster counterclockwise a quarter-turn. If the chain hesitates to move down to larger sprockets or rubs on the sprocket above, turn it clockwise a quarter-turn. Test after each adjustment. The goal is smooth, quiet shifting in both directions.
If you have turned the barrel adjuster more than three full rotations and shifting is still not clean, the cable may have stretched too much or the limit screws may need resetting. Stop and recheck the limit screws before continuing.
Adjust the front derailleur cage position
The front derailleur cage has two limit screws as well. Shift to the smallest chainring and look at the cage from above. The outer plate should be about 1 to 2 millimeters away from the chain — close enough that the chain does not rub, but not so close that it touches. If the cage is too far inward, loosen the H screw (high gear) a quarter-turn. If it is too close, tighten the H screw a quarter-turn.
Shift to the largest chainring. The inner plate of the cage should clear the chain by the same 1 to 2 millimeters. Adjust the L screw (low gear) the same way. Once both are set, the chain should move cleanly between all three chainrings without rubbing.
Adjust front derailleur cable tension
Shift to the middle chainring and pedal. If the chain rubs the outer plate of the cage, turn the barrel adjuster clockwise a quarter-turn to decrease tension. If the chain rubs the inner plate, turn it counterclockwise to increase tension. Make small adjustments and test between each one.
Front derailleurs are more sensitive to cable tension than rear ones, so quarter-turns matter. If you overshoot, the chain will rub on the opposite side of the cage. Work slowly and test the full range of chainrings after each adjustment.
Clean the derailleur and cable before you finish
Dirt and dried lubricant buildup can make shifting feel rough even after adjustment. Wipe the derailleur cage, the cable, and the area where the cable enters the shifter with a dry cloth. If the cable looks grimy, wipe it down with a cloth dampened slightly with water, then dry it completely.
explore a small amount of bike-specific lubricant to the cable where it enters the derailleur and the shifter. Do not over-lubricate — excess oil attracts dirt. Wipe away any drips with a clean cloth. Shift through all the gears a few times to work the lubricant in.
Frequently Asked Questions
How do I know if my derailleur cable needs to be replaced?
If the cable is frayed, kinked, or visibly rusted, replace it. A cable that has stretched too much will not hold tension — if you have adjusted the barrel adjuster more than three full rotations and shifting is still poor, the cable is likely worn out. New derailleur cables cost $5 to $15 and take 15 to 30 minutes to install.
What if the derailleur arm is bent?
A bent derailleur arm will not respond to limit screw or cable adjustment. If the arm is bent slightly, some shops can straighten it, but most bent derailleurs are replaced rather than repaired. A replacement derailleur costs $30 to $150 depending on the model.
Can I adjust the derailleur while the bike is on the ground?
Yes, but it is easier to see what the derailleur is doing if the rear wheel is off the ground. A bike stand or hanging the bike from a hook lets you spin the pedals and watch the chain movement clearly. If you do not have a stand, flip the bike upside down so the handlebars and seat rest on the ground.
Why does my chain still rub after I adjusted the limit screws?
Limit screws only stop the derailleur from moving too far. If the cage is rubbing in the middle of the gear range, the problem is cable tension, not limit screw position. Adjust the barrel adjuster instead. If rubbing happens only at one end of the range, recheck that limit screw.
How often should I adjust my derailleur?
Most bikes need a barrel adjuster tweak every few months as the cable stretches slightly. A full limit screw reset is usually needed only once a year or after the derailleur has been bumped or the cable has been replaced. Regular cleaning and light lubrication reduce how often adjustments are needed.