Things You'll Need:
- Hex wrenches
- Screw drivers: narrow straight blade and #2 Phillips
- Needle nose pliers
- Grease
- Light lubricant
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Step 1
Remove the old derailleur. Start by placing your bike on a bike stand, and then shift into the lowest cog so that you have less tension on the chain. With the proper sized hex wrench, detach the old derailleur from the hanger by loosening the screw and detaching any cables. Once the derailleur is loose, detach it from the bike and unloop the chain.
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Step 2
Install the new derailleur. Grease the threads of the bolt and screw it into position with your hex wrench. Typically this requires a 6 mm hex wrench. Tighten the bolt snugly and check that the derailleur is properly positioned on the hanger. Be sure that the hanger is straight, particularly if you're replacing the derailleur because of an accident or wreck.
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Step 3
Put the chain on the new derailleur. Be sure that the shifter is set for the smallest cog, and then carefully loop the chain over the sprockets. Be careful not to get any kinks in the chain while doing this. When the chain is properly threaded through the new derailleur, set the shifter to the lowest gear.
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Step 4
Reattach the shifter cable to the rear derailleur. Make sure the shifter is set to the lowest gear, and then grasp the cable end with needle nose pliers. Pull the cable end through the rear derailleur's anchor bolt, and while holding it with the needle nose pliers, tighten the screw of the anchor bolt. The anchor bolt may use a Phillips screw or a hex bolt. In either case, use the proper tool and tighten securely. There should be very little slack, if any, in the cable when you've completed this step.
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Step 5
While the bike is still on the work stand, test the shifting. Tighten or loosen the cable if necessary to facilitate smooth shifting. Be sure to hold the cable in place with your needle nose pliers when performing this step. It's also useful to mark the position of the cable in the anchor bolt before you adjust it--this allows you to judge the degree of adjustment that's necessary.
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Step 6
Test ride the bike and ensure that your adjustments have been made properly.
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Step 7
After your test ride, recheck all the bolts you've tightened to make sure that they're still tight. Apply some lubricant to the chain when you've completed your work.
