Bicycle gear cables, also known as derailleur cables, wear out because of excess grime and grit. These cables stretch and erode, causing misfires in the shifts. Changing the cable on the gearing is a matter of replacing the derailleur cable. To save money on costly shop repairs, change the cable at home and keep the extra money in your pocket.
Place the bike in the work stand. Shift the gears down to the easiest and smallest rear gear.
Turn the barrel adjuster on the back of the derailleur until the cable and barrel come off the derailleur. Go to the shifter on the handlebar and unscrew the barrel adjustment until the cable and barrel come off the shifter.
Follow the cable over the frame and remove it from each frame cable housing. Place the old cable and housing next to the new cable and housing and cut out a piece of the new cable/housing in the same length as the old.
Grease the wire cable and insert it into the cable housing. Cut 1.5 inches of the housing off of each end. Slide a ferrule -- a small metal cup/sleeve -- onto each side of the cable housing so the wire extends out of the ferrule. The ferrule keeps the wire in the housing.
Use the screwdriver to tighten the derailleur setscrew once the cable is inserted into the derailleur. Turn the barrel adjuster to the right until the cable is locked in the derailleur. Push the handlebar/shifter end of the cable into the shifter and tighten the barrel adjuster to the right.
Turn the pedals while the bike is still in the work stand and run through the gears. Take note of sloppy or missed shifts in the gears. Turn the barrel adjuster off the derailleur to the right until the gears shift smooth and no sprockets are missed.