How to Modify a Rear Derailleur
- 1). Locate the small protruding high and low gear limit screws at the back of the derailleur body. They are usually denoted with the letter "H" and "L."
- 2). Shift to the highest gear (smallest cog). Tighten or loosen the high gear limit screw in half-turns using a Phillips or flat head screwdriver until the derailleur's top pulley wheel is aligned with the cog.
- 3). Shift to the lowest gear (largest cog). Tighten or loosen the low gear limit screw, also in half-turns, until the top pulley wheel lines up with the cog. Proper alignment is important here, as a screw that is too loose allows the derailleur to move the chain into the spokes.
- 4). Locate the angle adjustment screw (sometimes called the "B-tension" screw). It is a protruding screw just above the H and L limit screws.
- 5). Shift to the lowest gear (largest cog) and note the relation of the top pulley wheel to the bottom cog teeth.
- 6). Tighten the B-tension screw if the pulley wheel is touching or rubbing against the cog. Loosen it if the top pulley wheel is too far away from the cog. Ideally, the pulley should be as close to the cog as possible without rubbing against it.
- 7). Test your bicycle's shifting by running through the gear sequence several times to ensure proper shifting in both directions. You may wish to add several drops of lubricant to your derailleur's screws. Wipe off the excess with an old rag.
