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Replacing the Rear Derailleur

You're riding along, sprinting up the trail, when you suck a stick into the rear derailleur. POW!  Your derailleur is toast. Believe it or not, it's not difficult to replace the rear derailleur yourself. Before replacing a "bent derailleur" make sure it's not just the derailleur hanger!

First, remove the idler pulley -- that's the bottom pulley of the derailleur. This pulley holds the chain inside the derailleur mechanism. Without it, the derailleur can slide backwards away from the chain.

If you can't (or don't want to) remove the idler pulley from your new derailleur, you'll need to break the chain.

See our section on chain repair.

Unscrew the derailleur from the derailleur hanger by inserting a hex wrench and turning counter-clockwise.

The derailleur will now come away from the hanger.

Remove the derailleur cable by loosening the hex bolt on the cable retaining clamp. Take the end cap off the cable, and draw the cable through the derailleur.

Put the new derailleur into position, holding it up and back (clockwise) from its usual position, so the tension adjusting screw is above the notch on the hanger.

Thread the mounting bolt into the hanger.

Route the chain through the derailleur. If you took the idler pulley off, put it above the chain, then bring the chain down and back into the cage of the derailleur. Now attach the idler pulley.

If you split the chain, route it by hand. It goes forward ABOVE the top pulley, down in FRONT of the pulley, around the BACK of the lower pulley, then forward BELOW the bottom pulley. Fix the chain.

Back off any cable-tension adjusters (usually found where the cable enters the derailleur and sometimes at the shifter) so you've got room to adjust the tightness of the cable when it's time to tune up the shifting.

Push the derailleur cable through the receptacle on the back of the derailleur. Pull the cable hard to remove any obvious slack. Then relax your pull on the cable and thread it through the cable clamp. Screw in the cable clamp bolt to tighten it down onto the cable.

The derailleur is now installed. But it's not ready to shift gears yet. Next you'll need to set the limiting screws, and adjust the cable tightness. See our section on rear derailleur tuneup.

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