The Shimano 105 rear derailleur is a component in Shimano’s line of road-oriented bicycle parts. The rear derailleur moves the chain between rear sprockets. The derailleur is controlled by a hand shifter, which is connected to the derailleur by a single cable. As the cable stretches with use, response from the derailleur becomes less accurate. Periodically adjusting the derailleur cable restores crisp response and precise shifting.
Use the right-hand shifter to shift the derailleur and chain to the outermost rear sprocket.
Locate the cable pinch bolt on the underside of the Shimano 105 derailleur. The pinch bolt attaches the cable to the derailleur.
Use a 5 mm Allen key to loosen the pinch bolt. The cable will go slack.
Locate the derailleur cable adjuster barrel. The cable passes through the center of the barrel before passing into the body of the derailleur.
Turn the cable adjuster barrel all the way into the body of the derailleur. Then give the adjuster barrel two full turns in the opposite direction.
Pull the end of the cable tight, removing slack. Use the 5 mm Allen key to tighten the pinch bolt back onto the cable.
Use the right-hand shifter to shift the derailleur and chain to the next sprocket over. Give the barrel adjuster a quarter-turn counterclockwise if derailleur response is sluggish. Try shifting again, and repeat the adjustment as needed.
Shift the derailleur and chain to the middle rear sprocket. Stand behind the bicycle and eye the alignment between the chain and the upper derailleur pulley. The two should be perfectly aligned.
Adjust the alignment as needed. To move the upper derailleur pulley to the left, turn the adjuster barrel counter-clockwise. To move the upper derailleur pulley to the right, turn the adjuster barrel clockwise.