The process of indexing is to line up the guide pulley with the cogs so that each incremental shift lines up with each cog. The barrel adjuster allows us to make these adjustments. A quick note is that there is a range of acceptable adjustments, meaning that there may be more than one barrel adjuster position that results in good shifting performance.
!!!SHOW ALIGNMENT OF DERAILLEUR WITH THE COGS!!!
Start on the smallest cog. Pedaling at a normal riding cadence, shift the shifter only one indexed click, not more than one click. We want this one click to shift one, and only one gear. If the chain did not make it to the next gear, return the shift lever to the outermost click, and turn the barrel adjuster one full turn counter-clockwise. Try the shift again and repeat the process until it makes the shift. If you have un-threaded the barrel adjuster that it has come out, or has nearly come out, thread the barrel back in fully and then out one or two turns. Make sure that you are on the furthest outward shift position and the smallest cog, then remove the slack from the cable at the pinch bolt.
!!!SHOW CABLE PULLING!!!
If you shift the shifter one click and the derailleur moves two sprockets, shift back to the first cog, turn the barrel adjuster clockwise one turn, and try the shift again. Now that our chain is on the second sprocket after one click of the shifter, the shifting can be fine-tuned.
Turn the barrel adjuster until it is clearly out of the acceptable range of the first shift. You will hear noise when pedaling. Make sure that the source of the noise is coming from the chain beginning to strike the next inboard cog, then slowly turn the barrel adjuster clockwise until the noise goes away. While this is an adequate setting for this cog, you must now check each subsequent cog in the cassette one at a time. Shift and listen at each position for any excessive noise in the drivetrain. If you hear a noise in any cog, turn the barrel adjuster clockwise one-quarter turn. Test the shift to that cog again, and listen for any excessive noise. Repeat and continue to check until you find the barrel adjustment that allows good shifting in every rear cog, with the exception of the largest cog. The shift to the largest cog will be done later.
Now, shift outward in every cog, checking for excessive noise and good shifting performance. If any of these shifts are slow coming outward, that can be improved by another quarter turn clockwise at the barrel adjuster. Our indexing is now properly set and it’s time to move the L-limit screw adjustment.