Today’s question came in response to our video on how to tune Shimano Di2 rear derailleurs. To keep up to date on all of the Ask a Mechanic videos we make each week, subscribe to the Art’s Cyclery YouTube page where you’ll also find many other helpful and fun videos.
Question: Hi, I hit a bump today and my gears stopped working and is stuck in one gear. I thought it was the battery, but I charged the battery and it is still the same problem. If I hold the control switch for a longtime, the gears change and go up and down, but it will not change on the levers, front or rear. Please help if you can, if there is a reset button or something. From: Moses
Answer: Sounds like a loose connection to me, as I’ve seen this before. What I suspect happened is that your Di2 shifter wires weren’t fully inserted into the lever body and when you hit the bump your hoods may have moved on the handlebar (perhaps nearly imperceptibly) and the wire popped out of its socket.
Peel back your hood and inspect the connection. Use the Di2 wire tool to ensure that you get the wire fully seated into the lever socket.
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