What's wrong with your gears and how to fix it

Bicycle gears slip, grind, or refuse to shift because the derailleur—the mechanism that moves the chain between sprockets—has fallen out of adjustment, or because the cable that controls it has stretched or frayed. Most gear problems come from one of three causes: the derailleur limit screws are set wrong, the cable tension needs adjustment, or the chain has worn out. You can fix the first two yourself with basic tools. A worn chain requires replacement, which is straightforward but does require a chain tool.

Before you start, shift to the smallest chainring in front and the smallest sprocket in back. This is the safest position to work from. Spin the pedals by hand to see whether the chain moves smoothly or catches. Listen for grinding or clicking sounds as it moves through each gear.

Key Takeaways

  • Most shifting problems come from a derailleur that is out of adjustment, not from a broken part, and can be fixed with a screwdriver and an Allen wrench.
  • The two limit screws on the derailleur stop the chain from falling off the smallest and largest sprockets, and they must be set correctly before you adjust cable tension.
  • Cable tension controls how quickly the derailleur moves between gears, and you adjust it by turning the barrel adjuster on the cable housing, not by loosening the cable itself.
  • A chain that skips under load or makes a grinding sound may be worn out and need replacement, which requires a chain tool to remove the old chain and install the new one.
  • If the derailleur itself is bent or cracked, or if the chain has broken links, replacement is the only fix and these parts are inexpensive.

Identify which derailleur is causing the problem

Bicycles have two derailleurs: the front derailleur moves the chain between the chainrings (the large sprockets near the pedals), and the rear derailleur moves it between the sprockets on the wheel. Front derailleur problems usually show up as the chain rubbing on the cage or refusing to move to the largest chainring. Rear derailleur problems show up as slow or sluggish shifts, chain skipping, or the chain falling off the smallest or largest sprocket.

Shift through all the gears while standing still and pedaling slowly by hand. Note which shifts feel rough or don't happen at all. If the problem is in front, the chain will either rub the derailleur cage or stay stuck on one chainring. If it's in back, the chain will hesitate between sprockets or skip when you pedal hard.

Set the limit screws on the rear derailleur

The rear derailleur has two small screws labeled H (high gear) and L (low gear). These screws prevent the chain from falling off the smallest sprocket (H screw) or the largest sprocket (L screw). If these are set wrong, the chain will drop off the wheel or refuse to shift all the way to the end of the cassette.

Shift to the smallest sprocket in back (highest gear). Look at the derailleur from behind the bike. The two pulleys on the derailleur should line up vertically with the smallest sprocket. If the derailleur is too far inward, turn the H screw counterclockwise a quarter turn. If it's too far outward, turn it clockwise. Make small adjustments and test each time by shifting.

Now shift to the largest sprocket (lowest gear). The pulleys should line up with the largest sprocket. If the derailleur is too far outward, turn the L screw counterclockwise. If it's too far inward, turn it clockwise. Again, make quarter-turn adjustments and test.

Adjust cable tension on the rear derailleur

Once the limit screws are set, the cable tension controls how quickly the derailleur responds to your shifter. If shifts are slow or the chain struggles to move up the cassette, the cable is too loose. If the chain overshoots a gear or struggles to move down, the cable is too tight.

Locate the barrel adjuster on the cable housing where it meets the derailleur. Shift to the middle of the cassette and pedal slowly. If the chain is slow to move up (toward smaller sprockets), turn the barrel adjuster counterclockwise one full turn. If the chain is slow to move down (toward larger sprockets), turn it clockwise one full turn. Test the shift. Repeat in quarter-turn increments until the chain moves smoothly in both directions.

Do not loosen the bolt that clamps the cable to the derailleur unless the cable is frayed or you are replacing it. Adjusting tension is done only through the barrel adjuster.

Set the limit screws on the front derailleur

The front derailleur also has H and L screws. The H screw stops the chain from falling off the largest chainring, and the L screw stops it from falling off the smallest chainring. Front derailleurs are trickier to adjust because the cage must clear the chain on both sides.

Shift to the smallest chainring in front and the smallest sprocket in back. Look at the derailleur cage from the side. There should be a small gap—about the thickness of a credit card—between the cage and the chain. If the cage is too close, turn the L screw counterclockwise. If it's too far away, turn it clockwise.

Now shift to the largest chainring and the largest sprocket in back. The cage should again have a small gap on the outside of the chain. Adjust the H screw the same way: counterclockwise to move the cage away, clockwise to bring it closer. The cage should never touch the chain in any gear combination.

Adjust cable tension on the front derailleur

Front derailleur cable tension works the same way as the rear: the barrel adjuster controls how far the derailleur moves. Shift to the middle chainring and pedal slowly. If the chain is slow to move to the largest chainring, turn the barrel adjuster counterclockwise. If it's slow to move to the smallest, turn it clockwise. Make small adjustments and test.

Front shifts are usually less critical than rear shifts, so small delays are normal. The goal is smooth movement without the chain rubbing the cage.

Replace a worn or broken chain

A chain that skips under load, makes a grinding sound, or has visible rust or broken links needs replacement. You will need a chain tool (also called a chain breaker), which costs between $15 and $40 and is worth buying if you plan to maintain your bike regularly. Some bike shops will remove and install a chain for a small fee if you prefer not to buy the tool.

To remove the old chain, place it in the chain tool and push the pin out. Do not push the pin all the way through—stop when the chain separates but the pin is still partially in the link. This makes reinstalling easier. Remove the chain and measure its length by laying it next to the new chain. New chains come slightly long and must be shortened to match the old one's length.

Thread the new chain through the derailleur cage and around the smallest chainring and smallest sprocket. Overlap the ends and use the chain tool to push the pin back in until the chain is connected. Spin the pedals and shift through all gears to make sure the chain moves smoothly. If it binds, the pin may not be fully seated; remove and reinstall it.

When to replace the derailleur itself

If the derailleur cage is bent, cracked, or the pulleys are damaged, adjustment will not fix it. A bent cage can sometimes be straightened carefully with an adjustable wrench, but a cracked derailleur must be replaced. Rear derailleurs are inexpensive ($20 to $60 for basic models) and bolt directly to the frame. Front derailleurs vary more in price and design, so take a photo of yours to a bike shop to may support you buy the right one.

Removing a derailleur requires unbolting the cable and the derailleur itself from the frame. Installation is the reverse: bolt it on, thread the cable through the barrel adjuster, clamp it to the derailleur, and adjust the limit screws and tension as described above. If you are not comfortable doing this, a bike shop can install a new derailleur for $30 to $50 in labor.

Frequently Asked Questions

Why does my chain skip when I pedal hard?

A skipping chain usually means the cable tension is too loose, so the derailleur is not moving the chain fully onto each sprocket. Turn the barrel adjuster counterclockwise a quarter turn and test. If skipping continues, the chain or cassette may be worn out and need replacement. A worn chain stretches and no longer fits the sprocket teeth properly.

How do I know if my cable is broken?

A broken cable will not move the derailleur at all, no matter how much you turn the barrel adjuster. You will also see fraying or a visible break in the cable itself. Replacement cables are inexpensive ($5 to $15) and come with housing. Remove the old cable by unbolting it from the derailleur, thread the new one through the housing, and clamp it back on. Adjust the limit screws and tension as normal.

Can I adjust gears without special tools?

You need a screwdriver (usually Phillips head) to adjust the limit screws and a 5 mm Allen wrench for most derailleurs. These are basic tools that cost a few dollars. A barrel adjuster can be turned by hand, so no tool is needed there. A chain tool is only necessary if you need to replace the chain.

What if my bike has internal hub gears instead of derailleurs?

Internal hub gears are sealed inside the wheel and do not have derailleurs or cables on the outside. Adjustment is usually limited to cable tension on the shifter. Consult your bike's manual or a shop, as different hub systems have different adjustment points.

How often should I clean and lubricate my chain?

Clean and lubricate your chain every 100 to 200 miles, or whenever it looks dry or dirty. Use a chain-specific lubricant, not general-purpose oil, which attracts dirt. Wipe off excess lubricant with a rag. A clean, well-lubricated chain shifts more smoothly and lasts longer.