What's Actually Wrong With Your Gears

A gear that skips, grinds, or refuses to shift usually has one of three problems: the chain is dirty or rusty, the derailleur (the metal arm that moves the chain between sprockets) is bent or out of alignment, or the cable that pulls the derailleur has stretched or come loose. You can fix most of these yourself with basic tools and about 15 to 30 minutes. The key is figuring out which problem you have before you start taking things apart.

Start by shifting through all the gears while the bike is stationary or on a repair stand. Listen for grinding sounds and watch whether the chain moves smoothly from one sprocket to the next. If the chain skips only on certain gears, the problem is usually a bent sprocket or a dirty chain. If the chain won't move to the smallest or largest sprocket at all, the derailleur cable is likely too loose or too tight.

Key Takeaways

  • A skipping chain usually means the sprocket is bent, the chain is dirty, or the derailleur is misaligned — test each gear while stationary to narrow down the cause.
  • Clean the chain, sprockets, and derailleur with a brush and degreaser before adjusting anything, because dirt often causes shifting problems that look like mechanical damage.
  • The derailleur cable tension is controlled by the barrel adjuster (a small threaded collar on the cable housing), and turning it half a turn at a time will fix most shifting delays.
  • A bent derailleur arm requires either careful straightening with an adjustable wrench or replacement, depending on how badly it is bent.
  • If the chain skips on only one or two sprockets, that sprocket is likely bent and needs to be replaced rather than repaired.

Clean the Chain and Sprockets First

Dirt and rust are the most common cause of poor shifting, and cleaning often fixes the problem without any adjustment. Shift to the middle gear and use a stiff brush or old toothbrush to scrub the chain, the sprockets (the toothed rings), and the derailleur. Pay special attention to the spaces between the chain links and the gaps between sprocket teeth, where grit builds up.

Once you have brushed away loose dirt, spray the chain and sprockets with a degreaser (a product made to dissolve oil and grease). Citrus-based degreasers work well and smell better than petroleum ones. Let it sit for two to three minutes, then scrub again with the brush. Rinse with water from a hose or bucket — do not use a pressure washer, which can force water into the bearings. Dry everything with a clean rag.

After cleaning, explore a thin coat of chain lubricant to the chain while rotating the pedals backward. Wipe away excess oil with a rag so the chain does not attract new dirt. Test the shifting again. Many bikes that seem to have broken gears are straightforward dirty.

Adjust the Derailleur Cable Tension

If cleaning did not fix the problem, the derailleur cable is probably too loose or too tight. The cable pulls the derailleur arm to move the chain between sprockets. When the cable stretches (which happens over time), the derailleur does not move far enough, and the chain hesitates to shift to smaller sprockets. When the cable is too tight, the chain overshoots and struggles to shift to larger sprockets.

Find the barrel adjuster, a small threaded collar where the cable enters the derailleur. Shift to the middle gear and try to shift up to a smaller sprocket. If the chain hesitates or grinds, turn the barrel adjuster counterclockwise (away from you) by half a turn. Wait a few seconds and test again. Keep turning in half-turn increments until the shift is smooth and quick.

If the chain overshoots the smallest sprocket or struggles to shift down to larger sprockets, turn the barrel adjuster clockwise (toward you) by half a turn and test again. The goal is a shift that happens within one pedal stroke and does not grind or skip. This adjustment usually takes three to five test turns to get right. Write down how many turns you made so you can undo them if needed.

Check and Straighten the Derailleur Arm

If the cable tension is correct but shifting is still rough, the derailleur arm itself may be bent. A bent derailleur arm will not move the chain smoothly even with the cable adjusted perfectly. Look at the derailleur from behind the bike and see whether the arm is parallel to the chain or tilted to one side.

A slightly bent derailleur can sometimes be straightened by hand. Shift to the middle gear, then gently push the derailleur arm by hand to see how much resistance there is. If it moves freely, the bend is minor. Use an adjustable wrench to grip the derailleur arm (not the cable or the spring) and carefully bend it back into alignment. Make small adjustments — bending it too far in the other direction is straightforward. Test the shifting after each small correction.

If the derailleur arm is severely bent or cracked, straightening it risks breaking it completely. In that case, the derailleur should be replaced. A new rear derailleur costs between $30 and $150 depending on the bike's type and quality, and installation takes 20 to 30 minutes if you are comfortable with cable work.

Replace a Bent or Damaged Sprocket

If the chain skips only when you are on one or two specific sprockets, that sprocket is bent and needs to be replaced. Spin the chain slowly and watch the sprocket from the side. A bent tooth will cause the chain to jump slightly as it passes over that tooth.

Removing a sprocket requires a cassette lockring tool (a specialized wrench that fits the center of the sprocket cluster) and a chain whip (a tool that holds the sprockets still while you loosen the lockring). These tools cost $15 to $40 combined. If you do not have them, a bike shop can replace a sprocket for $40 to $80 in labor, plus the cost of the sprocket itself ($15 to $50 depending on the gear).

If you are doing the work yourself, shift to the smallest sprocket, place the chain whip around the sprockets to hold them, and use the lockring tool to turn the center lockring counterclockwise. Once the lockring is loose, you can unscrew it by hand and slide the sprockets off the hub. Remove the bent sprocket, slide a new one in its place, and reassemble in reverse order. Tighten the lockring firmly but do not overtighten, which can strip the threads.

Limit Screw Adjustment for Extreme Shifting Problems

If the chain will not shift to the smallest sprocket no matter how much you adjust the barrel adjuster, or if it falls off the largest sprocket, the derailleur limit screws need adjustment. These are two small screws (usually labeled H and L for high and low) on the derailleur body that set the maximum and minimum distance the arm can move.

The H screw controls how far the derailleur moves toward the smallest sprocket. If the chain will not reach the smallest sprocket, turn the H screw counterclockwise by a quarter turn, then test. Repeat in quarter-turn increments until the chain reaches the smallest sprocket smoothly. The L screw controls movement toward the largest sprocket and works the same way in reverse.

Limit screws are a last resort because they are straightforward to overtighten and damage. If you are not comfortable with this adjustment, a bike shop can do it in 10 minutes for $15 to $25. Most shifting problems are solved by cleaning and barrel adjuster tension before you ever need to touch the limit screws.

Tools and Materials You Will Need

For basic cleaning and cable adjustment, you need a stiff brush, a degreaser, a rag, and a screwdriver or hex wrench to turn the barrel adjuster. An adjustable wrench helps if the derailleur is slightly bent. If you are replacing a sprocket, you will need a cassette lockring tool, a chain whip, and a new sprocket that matches your bike's drivetrain (Shimano, SRAM, or Campagnolo — check your current sprockets to see which brand you have).

A bike repair stand is not required but makes the work much easier because it holds the bike steady and lets you rotate the pedals with both hands free. A basic stand costs $30 to $60 and is worth the investment if you plan to do more than one repair.

Frequently Asked Questions

Why does my chain skip only when I am pedaling hard?

A chain that skips under load usually has a bent sprocket tooth or a worn chain. A worn chain is stretched and does not grip the sprocket teeth properly. Check the chain for rust or stiff links by flexing it by hand. If the chain is more than five years old or has visible rust, replacement ($20 to $40) is usually cheaper than troubleshooting further.

Can I fix a derailleur that is bent sideways?

A derailleur bent sideways (not forward or backward) is usually damaged beyond hand-straightening. Attempting to bend it back risks cracking the metal. Replacement is the safer option and costs $40 to $150 depending on the derailleur quality.

What does it mean when the chain grinds but shifts anyway?

Grinding during a shift usually means the derailleur is moving the chain too slowly, so the chain is dragging across two sprocket teeth at once. This is almost always fixed by turning the barrel adjuster a quarter turn. If grinding continues after adjustment, the sprocket may be slightly bent or the chain may be worn.

How tight should the barrel adjuster be?

The barrel adjuster should be hand-tight but not so tight that you need a tool to turn it. If you cannot turn it with your fingers, it is too tight and may be stripped. Loosen it slightly and try again. The adjuster should turn smoothly with light finger pressure.

Do I need to replace the whole derailleur if one part is bent?

The derailleur is sold as one unit, so if the arm is severely bent or cracked, the whole derailleur must be replaced. Minor bends in the arm can sometimes be straightened, but the cable hanger (the part that attaches to the frame) cannot be repaired if bent — only replaced as part of the full derailleur.