How to Replace a Rear Derailleur on a Trek 620 Bicycle
Although an older model, the Trek 620 bicycle incorporates relatively modern gearing. Minus a few superficial details, the rear derailleur is nearly indistinguishable from many of today's models, and one that is well adjusted and maintained is likely to work almost as well. The rear derailleur on a Trek 620 bicycle can easily be removed and a new one installed. These derailleurs control the gearing at the rear of the bike, shifting the chain on command from one sprocket to another.
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Things You'll Need
- Allen wrenches, 5 and 3 mm
- Wire cutters
- Needle nose pliers
- Metal cable crimp
Instructions
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Removal
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1
Use a 3 mm Allen wrench to remove the bolt at the center of the tension pulley. This is the lower of the two pulleys dangling from the bottom of the rear derailleur.
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2
Slide the pulley free of the derailleur. Removing the tension pulley allows you to free the derailleur from the chain without separating the chain.
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3
Use a 5 mm Allen wrench to loosen the shift cable anchor bolt at the bottom of the derailleur. This bolt "anchors" the shift cable to the derailleur.
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4
Clip the metal crimp from the end of the cable using wire cutters, then pull the cable from the body of the derailleur.
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5
Remove the fixing bolt from the center of the derailleur, using the 5 mm Allen wrench. This bolt "fixes" the derailleur to the frame of the bicycle. Remove the old derailleur from the bicycle.
Replacement
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6
Repeat Steps 1 and 2 above, and remove the bolt from the center of the tension (or lower) pulley, and remove the pulley from the new derailleur.
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7
Attach the fixing bolt on the back of the derailleur to the bike. Make sure the chain runs in front of the derailleur's jockey (or upper) pulley. Tighten the fixing bolt with the 5 mm Allen wrench.
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8
Press the idler pulley (the one you just removed) against the inside of the chain in front of where the pulley attaches to the derailleur. Press the pulley fully in place, and secure it to the derailleur by threading its bolt back through the center and then tightening it.
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9
Pass the shift cable through the hole at the back end of the derailleur, and pull the cable taught with a pair of needle nose pliers. While pulling the cable taught, tighten the anchor bolt at the bottom of the derailleur onto the cable. This will hold the cable in place.
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10
Attach a new metal crimp to the end of the cable, and squeeze the crimp in place with needle nose pliers. These metal crimps keep cable ends from fraying.
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