How To Set Up And Adjust Your Rear Mech | Gear Indexing Basics, by GMBN Tech on YouTube. 10 min 54 s.
- Video length
- 10 min 54 s
- Time to do it
- 30 minutes
- Difficulty
- Medium
- Steps
- 7
What you need
Steps
Shift to the smallest rear cog and release any cable tension at the barrel adjuster so the cable runs slack.
Set the high limit screw so the upper jockey wheel lines up directly under the smallest cog. Turn the screw in small quarter turns.
Push the derailleur by hand toward the largest cog and set the low limit screw so the jockey wheel sits under the biggest cog without going past it.
Clamp the cable at the derailleur with the shifter in the highest gear and the cable pulled snug but not tight.
Shift up and down the cassette and fine-tune cable tension with the barrel adjuster until each shift is crisp and quiet.
Set the B position so the upper jockey wheel sits about 5 to 6 mm from the largest cog teeth.
Work through the gears again and check for slow shifts, chain rub or overshifting, adjusting tension or limits as needed.
Tips and common mistakes
Turn limit screws a quarter turn at a time so you do not overshoot and drop the chain.
If shifts are slow going up the cassette, add cable tension with the barrel adjuster.
Check the derailleur hanger is straight first, since a bent hanger spoils any indexing.
Keep your hands and clothing clear of the spinning wheel and chain while testing shifts.
Questions
Do I need to replace the cable to index my gears?
No. If the cable moves freely and is not frayed, you can index the gears with the existing cable and barrel adjuster.
Why does my chain fall off the biggest cog?
The low limit screw is set too far out. Turn it in until the jockey wheel stops under the largest cog.
What is the B screw for?
It sets the gap between the upper jockey wheel and the cassette, which affects shift quality and chain wrap.
This guide was drafted from the video's details and general task knowledge. It has not been checked against the full video. Check the video and relevant product instructions before following a procedure. Report a correction.
