Shimano's Deore derailleur is a high-level rear derailleur for mountain bikes. The derailleur is meant to be used in rough, muddy and obstacle-filled terrain, meaning it is overbuilt, strong and accurate. A derailleur of any calibre, however, will not work correctly unless it is adjusted properly. Learn how to adjust your Deore derailleur at home, and save time and money over taking your bike to the local bike shop to have the procedure completed.
Loosen the cable stop bolt of the Deore derailleur with a 5mm hex wrench. Turn the pedals of the bike by hand to allow the chain to fall to the smallest cog.
Look from behind the bike and inspect the alignment of the chain with the small cog. If the derailleur pulls the chain to the right of the cog, tighten the high limit screw (marked with an H). If the derailleur pulls the chain to the left of the cog, loosen the high limit screw. The derailleur should keep the chain perfectly in line with the small cog.
Pull the cable through the rear derailleur cable stop using a pair of needle nose pliers, then tighten the cable stop using a 5mm hex wrench. Spin the cranks of the bike by hand and shift the chain up to the largest cog via the shifter thumb lever.
Spin the cranks and watch the chain to determine whether or not it is aligned properly with the large cog on the cassette. If the chain is being pulled to the right of the cog, or did not shift completely onto the cog, loosen the low limit screw (marked with an L) using a Phillips head screwdriver. If the chain shifts too far, and is in danger of coming in contact with the spokes of the wheel, tighten the low limit screw until it is aligned correctly.
Take the bike for a short test ride. Shift through all the gears of the rear shifter one at a time. Shifting should be quick and crisp, without the chain bouncing from gear to gear or skipping on the rear cassette. If all is well, go out for a ride and enjoy the accuracy of a well-tuned Deore derailleur.