A derailleur is the component on your mountain bike that pushes or pulls the chain from sprocket to sprocket as you change gears while riding. There is a derailleur on the front for the chainrings and one on the back for the gear cluster. As you shift gears with the handlebar controls, you add or remove tension from the springs in the derailleur body, causing the chain to shift. If your derailleur is not properly adjusted, you may have difficulty shifting gears or find that the chain is constantly coming off your bike.
Step 1
Shift the mountain bike into the lowest gear. This is the largest sprocket on the rear and the smallest chainring on the front. Locate the B-tension screw at the pivot point where the derailleur body attaches to the tension arm. Tighten the B-tension screw just enough so the derailleur pulley clears the large rear sprocket without rubbing on it.
Step 2
Find the high- and low-gear limit screws on the derailleur body. They are the pair of screws just in front of the shifter cable adjustment barrel. Shift the bike into the highest gear combination, which is the smallest sprocket in the rear and the largest on the front. Feel the shift cable for tension while the gears are in this position. If some tension is present, turn the barrel adjuster clockwise until none is present.
Step 3
Watch the chain as you turn the pedals forward by hand. If the chain appears to be leaning off the smallest gear sprocket, insert a screwdriver into the high-gear limit screw and tighten it. The high-gear limit screw is the screw closest to the front of the bike out of the pair. If the chain is rubbing on the next sprocket, loosen the high-gear screw. Tighten the tension adjustment barrel a quarter-turn at a time until the gears shift smoothly again.
Step 4
Shift the derailleur back to the lowest gear combination. Look down the line of the chain from the back of the bike and check if it is centered on the gear sprocket. Tighten or loosen the low-gear limit screw in the same manner you used for the high-gear limit screw.
Step 5
Adjust the derailleur through all the gears and check to make sure the chain sits centered on each gear sprocket. If the chain is rubbing on the next sprocket, tighten the barrel adjuster. If the chain is leaning out of the sprocket like it will shift out of the gear, loosen the barrel adjuster.
Step 6
Place a drop or two of light oil on each of the pivot points in the derailleur. Wipe off the excess lube before you go riding again, as the dust and dirt of a mountain trail can quickly gather in the lubricant.
Tips and Warnings
- Check the derailleur to see if it is bent before you begin making adjustments. It is common for the mounting tube of the derailleur to become bent, thus throwing off the action of the mechanism. You need to completely remove the derailleur to correct this bend.
Things You'll Need
- Phillips screwdriver
- Light oil
- Rag
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