Back in December 2020 I wrote a short post about my Bafang Chainline Problem and how I fixed my chain from dropping off the front chainring. It was a simple solution. I reinstalled the front derailleur and adjusted the derailleur limiter screws to perfectly align the front derailleur with the chainring. The derailleur served as a chain drop guard to keep the chain from falling off the chainring. While this solution cured the chain drop problem and I was able to use all the gears on my rear cluster, I was getting an annoying chain rub on the front derailleur on my top (highest) and bottom (lowest) gears.
Although I could live with the chain rub on short rides, on longer rides it was becoming unbearable and I avoided using the top and bottom gears. With the Bafang Monster Bike Build I wanted to solve this problem. I was hoping I could adjust the Shimano XT indexed triple chainring front shifter to micro adjust the front derailleur just enough for a top, middle, and bottom gear range shift. However, the index shifter cable pull was too long because the derailleur limiter screws were significantly limiting the derailleur movement to stop the chain drop.
To solve the problem, I used an old school SunRace SLM10 Friction Thumb Shifter, approximately $15 for a set. Now when I hear the chain rubbing on the front derailleur, I just give the thumb shifter a little nudge to make a micro adjustment on the front derailleur to eliminate the noise. And I don’t have to worry about the chain dropping off the front chainring because the front derailleur limiter screws will not let the derailleur move far enough to drop the chain. I can use all nine gears on the rear cluster with no chain drops and no chain rub on the front derailleur. Problem solved!
For detail on the original e-bike build see Bafang E-bike Conversion.