Although Shimano manufactures multiple shifting systems (Dura-Ace, DXR, Deore DX and Ultegra), they all share a common adjustment method. Adjusting the shifting on a bike means that the tension in the cable connecting the shifting mechanism to the rear derailleur must be tightened or loosened. Cable tension is altered near the shifting lever that is integrated into the handlebar brakes on road bikes or on the grip of mountain bike handles.
Brake Handle Shifters
Shift to the smallest gear so that the cable is in the most relaxed position.
Pull back the rubber housing on the the brake hood to expose the pivot point on the brake handle where the shifting cable is inserted.
Loosen the cable barrel adjustment nut, which is located between the brake hood and the rear derailleur.
Pull the end of the cable at the brake hood until the cable is snug.
Tighten the cable barrel adjustment nut, then loosen it two complete turns.
Shift the bike through all gears to check for noise and ease of shifting. Repeat the process of loosening the barrel adjuster and tightening or loosening the cable as necessary to achieve the level of tension desired.
Remove the cover on the grip handle to expose the end of the shifter cable.
Remove the small set screw, using a hex or Allen wrench, that holds the cable in place. The cable should now move freely.
Loosen the cable barrel adjuster and pull the cable end out of the housing to remove any slack.
Tighten the barrel adjuster, re-attach the set screw and tighten.
Shift through all of the gears to test the tension and make sure that the chain moves smoothly from gear to gear. If not, remove the set screw and readjust the cable tension again.
If several adjustments cannot fix the problem, the cable may be worn. Take the bicycle to a qualified repair shop to have the cable replaced.
Before you try to adjust the rear derailleur, look closely to make sure it is not bent. Many times, particularly on mountain bikes, the exposed derailleur can get hit and knocked out of shape or alignment.