Q: How do you adjust a rear derailleur to shift smoothly?
A: You can set-up and adjust a rear derailleur on a mountain bike in five easy steps.
Step #1: Begin with the B screw adjustment. Shift into the largest rear cog (innermost) and adjust so the guide pulley on the derailleur is just clearing the sprocket on the cassette. If it is rubbing, add tension by turning the B screw clockwise. If the gap is too big, turn the B screw counterclockwise to close the gap.
Step #2: Shift down to the outermost (smallest cog) on the cassette and it is time to adjust the H screw adjustment. Be sure to remove any cable tension, as it can affect the H adjustment. If the guide pulley looks like it wants to pull the chain off onto your axle, tighten the H screw clockwise. If it looks like it wants to rub on the next gear, loosen the H screw counterclockwise.
Step #3: Shift back into the highest gear (innermost large cog) for the L screw adjustment. You may need to add tension back to the cable at this point, but we will adjust cable tension later. If the guide pulley looks like it is going push the chain into the spokes, tighten the L screw clockwise. If it wants to throw the chain down into the next gear, loosen the L screw until it is aligned with the innermost cog.
Step #4: Cable adjustment time. Loosen the pinch bolt, at the derailleur to free all tension from the cable. Inspect the cable for any damage and lubricate the cable if necessary. You can remove the cable, from the housing, and pull it through a rag with some degreaser on it. Next, pull it through a rag of your favorite lube such as TriFlow.
***Quick tip: Instead of using a crimp, to close off the end of the cable, try using some shrink tube or Gorilla glue to seal up the end in case you need to remove it again. This saves you from cutting off length every time you need to do cable maintenance.***
With the cable tension removed, turn in the cable tension adjustment knob all the way in and then back it out two turns. Pull all the slack out of the cable, and reattach it to the pinch bolt and clamp it down 44-60 inch-lbs.
Step 5: Final tweaking. Shift through all gears by going up two and down one and then down two and up one several times until the shifts are smooth and snappy. Adjust, by 1/4 turns, cable tension of any missed gears. If it is rubbing on a larger gear, it means there is too much tension on the cable and you need to loosen the cable by turning the adjuster clockwise. If it wants to jump down to a smaller gear, it needs more tension and you need to tighten it by turning the adjuster counterclockwise. Once smooth, apply a drop of lube to each adjuster screw and all pivot points of the derailleur. Now go out for a ride and celebrate!