A cable connects a Shimano Ultegra front derailleur to a gear shifter on the handlebar. When shifting gears on the bicycle, derailleur cable tension determines which direction the derailleur will pivot. When pivoting, the front derailleur forces the drive chain onto the selected chain ring, resulting in a new gear ratio. Derailleur cables stretch with use, and the lack of cable tension will cause the derailleur and shifter to operate less precisely over time.
Use the front Shimano Ultegra gear shifter to shift the derailleur and chain onto the smallest front chain ring. Complete the shift by lifting the rear wheel of the bicycle and turning the pedal forward.
Observe the routing of the cable from the derailleur to the shifter. The replacement cable will follow this exact path.
Use a 5mm Allen key to loosen the cable pinch bolt, just above the derailleur. The derailleur cable will go slack.
Use a pair of cable cutters to cut the protective end cap off the end of the cable.
Slide the cable free of the derailleur.
Squeeze the front brake lever to reveal the derailleur cable head inside the gear shifter.
Grasp the cable head with needle-nose pliers. Pull the cable free of the bicycle.
Squeeze the front brake lever and slide a new derailleur cable through the designated hole in the shifter. Seat the cable head inside the shifter by pulling the other end of the cable.
Route the new derailleur cable beneath the bicycle and through the cable guide on the underside of the bottom bracket shell. The new cable will follow the same path as the old one.
Do not attach the cable to the Ultegra derailleur yet. Instead, locate the adjuster barrel, midway along the cable.
Turn the adjuster barrel clockwise until it stops. Then turn the adjuster barrel two revolutions in the opposite direction.
Thread the cable beneath the cable pinch bolt. Pull the end of the cable, removing any slack. Use the 5mm Allen key to tighten the pinch bolt onto the cable.
Use the front gear shifter to try shifting the derailleur and chain onto the large chain ring. Complete the shift by lifting the rear wheel and turning the pedals forward. If the derailleur and chain fail to shift, the cable requires more tension.
Add tension to the cable by turning the barrel adjuster counter-clockwise. Try shifting again.
Continue to add tension to the cable until the derailleur and chain are able to shift effectively onto the large chain ring.