Align Derailleur Hanger

Step-by-Step Summary

1. Remove Derailleur: Unbolt the rear derailleur and let it hang carefully by the cable.
2. Install Gauge: Screw the alignment tool into the derailleur hanger threads.
3. Measure Vertical: Rotate the tool to the 6 o'clock position (bottom of wheel). Set the indicator pin to the rim. Rotate to 12 o'clock (top). check gap.
4. Bend: If there is a gap, gently pull/push the tool arm to bend the hanger until the pin touches the rim at both top and bottom.
5. Measure Horizontal: Repeat the check at 3 o'clock and 9 o'clock positions. Align as needed.
6. Tolerance: Aim for less than 3mm gap difference all the way around.
7. Reinstall: Remove tool, reinstall derailleur, and check shifting.

[!TIP] Aluminum hangers fatigue. If it is severely bent, it might snap when you try to bend it back. Always have a spare hanger handy.