Over time, cables running from the shifter to the derailleur stretch, causing the derailleur to not shift properly. This can be fixed by making adjustments to the rear derailleur. This involves setting the upper and lower bounds, which determine where the derailleur can travel to. Also, if it has been a long time since the cable itself has been tightened, that may be necessary as well.
No parts required.
Shift the rear derailleur so it is in the 8th gear position.
Using the phillips head screw driver, adjust the screw labeled with an H so that the derailleur lines up vertically with the 8th gear (the smallest one).
Set the low bound by shifting the rear derailleur to its 1st gear position. Adjust the screw labeled with a L, so the derailleur lines up vertically with the 1st gear.
If you are unable to get the low bound over far enough by adjusting the screw, try tightening the cable using the adjustment knob found on the shifter itself.
Shift the derailleur into either the 4th or 5th gear, and adjust the hex screw found on the back of the derailleur to make sure the derailleur lines up vertically with the gear the bike is in.
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