Shimano bicycle gears are know as some of the most accurate, quick shifting and accesible bike parts available on the market. However, they will only work the way they should if they are adjusted properly. Most bicycle shops can perform a gear adjustment while you wait, but why spend your hard earned cash getting your bike fixed when you can do it on your own, with tools you already own? Learn how to repair your Shimano gears and save time and money before visitting your local bike shop.
Spin the cranks of the bike forward and shift both shifters all the way down to the lowest gear. Loosen the cable stop on both the front and rear derailleurs to release the shift cables.
Look at the rear derailleur pulley system from the rear of the bicycle. The first pulley in the system should be aligned just beneath the smallest cog on the cassette. If the pulley pulls the chain to the right of the cog, tighten the high limit screw (on the body of the derailleur marked with an H) until the chain is in line. If the pulley pulls the chain to the left, loosen the high limit screw.
Observe the alignment of the chain with the front derailleur. Make sure that the chain does not rub on the inside of the derailleur. If it does, loosen the low limit screw on the body of the derailleur until you can spin the cranks quietly. Reattach the front and rear derailleur cables by tightening the cable stops with a five millimetre hex wrench.
Spin the cranks of the bicycle and shift both shifters up to their biggest gears. Observe first the alignment of the rear derailleur pulley with the large cog. If the chain is not centred beneath the cog, adjust the low limit screw (on the body of the derailleur marked with an L) until it lines up. Next, observe the alignment of the chain with the front derailleur. If the chain rubs on the derailleur, tighten the high limit screw on the body of the front derailleur until you can turn the cranks quietly.
Take the bike out for a test ride and shift through all of the gears. The derailleur system has now been completely reset, and you should notice that the quick and accurate shifts that Shimano's gears are known for has returned.