Di2 Rear Derailleur failure during Windmill Century

[tantra]

I had to abort my century ride yesterday because of a di2 9070 rear derailleur failure. The bike was shifting beautifully until just before the first rest stop. I wasn't pedaling hard. Suddenly, the RD made an uncommanded shift to the smallest cog. I heard clicks and whirls when I commanded shifts but the cage didn't move. Also, I could easily move the RD by hand, which I couldn't before. I tried the post-crash recover reset by holding the button down until the red light flashed and turning the cranks. The derailleur struggled to move. The front derailleur shifted fine. The Garmin was very confused.

Here's what I think caused the failure: I recently upgraded my Di2 9070 with the the 9150 battery and connectors so I had synchroshift with 9070 FD and RD. I didn't use the synchroshift but set manual to 'fast' shifting mode and noticed crisper shifts. I think the new software imposed loads beyond the design limits of the old 9070 mechanicals. I guess the RD failed first since it shifts way more often.

By the way, these 9070 derailleurs are in a mixed system with XG-1190 11-28t cassette, Praxis rings and KMC chain. Not sure how that figures in.

[Mep]

That's terrible news, sorry to hear. Hope you and your bike are fine otherwise.

[ms6073]

That sounds like what happens when the battery is nearly flat (<7% reserve I think). When was the last time you charged the battery? Does the status LED on the junction A flash red repeatedly when you depress and hold the shift lever?

[BdaGhisallo]

There's nothing wrong with the "design limits of the 9070" RD. I have been using mine with the fastest shifting mode for a few years now and have never had a problem. It sounds like your RD might be stuffed, but it has nothing to do with it trying to shift too fast. The E-Tube software wouldn't offer that option for setup if Shimano wasn't 100% sure it could handle it with aplomb.

[stockae92]

So this is not a battery issue but the RD mechanism failure?

[BdaGhisallo]

So this is not a battery issue but the RD mechanism failure?

Are you able to connect it to the E-Tube software and run a diagnostic test on it?

[rmerka]

Had the exact same thing happen to me. Never got an explanation but Shimano replaced it under warranty (through LBS) no questions asked.

[tantra]

It is definitely not a battery issue. The battery is almost new, was hot off the charger, and showed 100% on the Garmin after the RD failed. The RD failed when I connected to E-tube and ran the diagnostics. Something is obviously broken internally since the derailleur makes clicking noises without moving when I command shifts.