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How to Diagnose and Fix Common Drivetrain Problems

A Step-by-Step Walkthrough by Bike Man Dan

A skipping chain or clunky shift can make even the nicest bike feel awful. The trick is to approach drivetrain problems methodically, working through the simple checks first before diving deeper or making assumptions. Here’s a step-by-step process that works for most bikes that we’ve developed over many years of diagnosing all sorts of weird and wonderful issues!

1. Check for visible damage

Before you touch any adjusters, look closely at every part of the system:

  • Shifters & levers: are they cracked, bent, or pulling cable smoothly?
  • Cables (inner and outer): check for fraying, rust, or housing that’s kinked or split. Damaged cables are one of the most common causes of poor shifting, sometimes the damage is hidden inside the shifter or internal frame-routing.
  • Derailleur hanger: this small piece bends easily and is the number-one cause of skipping gears. If it’s not perfectly straight, no amount of tweaking will fix the issue—get it aligned or replaced first.
  • Derailleur body: inspect the cage for bends, make sure the pivots move freely, and check the limit screws aren’t bent or missing.
  • Barrel adjusters: if they’re seized, you’ll struggle to fine-tune indexing. A drop of penetrating oil can free them up.
  • Jockey wheels: look for broken teeth or excess sideways play. They’re cheap to replace and make a big difference to shifting.

Address anything here before moving on—especially hanger alignment.

2. Sanity check compatibility

Even if everything looks fine, mismatched parts can cause endless headaches. Double-check:

  • Cassette: count the sprockets.
  • Shifters: count the clicks. One must match the other.
  • Crankset/chainrings: make sure the chain is suited to the number of speeds (e.g. 9-speed chain on a 9-speed system).

If there’s a mismatch—say, a 10-speed shifter paired with an 11-speed cassette—you’ll never get smooth shifting until that’s fixed.

3. Set indexing (cable tension)

Once you know everything’s compatible, make sure one click equals one gear change.

  • Start in the smallest cog.
  • Use the barrel adjuster to add or release tension until each click moves the chain neatly onto the next cog.
  • Work up and down the cassette to confirm it’s consistent.

Small adjustments go a long way—a quarter turn is often enough.

4. Check the chain and cogs for wear

If the indexing feels right but the gears still crunch or slip under pressure, the problem might be wear:

  • Chain: use a chain checker tool. A stretched chain may have damaged your sprockets.
  • Cassette/chainrings: worn teeth look sharp or hooked. A new chain on old cogs may skip immediately. If the chain has gone >0.75% then you may need to replace the lot

Worn parts only get worse—replacing a chain early is far cheaper than replacing chain, cassette, and rings together. (See our full chain wear guide for more detail.)

5. Look for less obvious issues

If none of the above solves it, check for:

  • Missing spacers: especially behind the cassette on some freehub bodies.
  • Loose hub bearings: play in the wheel can make shifting unpredictable.
  • Freehub problems: worn out internals or damaged splines can cause bad indexing or slipping under load.

These are less common but worth ruling out before you throw in the towel.

Final Word

Most drivetrain issues boil down to either a bent hanger, poor cable condition, or worn chain/cogs. After that it’s likely incompatible parts. By working through checks in this order you’ll avoid chasing your tail—and learn to “read” what your bike is telling you.

Patience and method beat guesswork every time. Make one change at a time, test, and you’ll soon have your gears running smoothly again.

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