Ultegra Di2 rear mech failure

mr_quiggs

2018 RD-6870 rear derailleur on a Liv Langma. No issues for 3 years, but last week the rear mech was not working when picked up bike to go on ride. No issues on ride the previous day.

- No crashes
- All cables connected correctly, removed and clicked back in with tool*
- Battery fully charged - full green LED on bar-end A-junction box when holding any shifter
- Front mech shifts perfectly
- Rear mech is stuck on the 27 sprocket.
- When trying to shift, green LED comes on as normal, but there is no movement or sound whatsoever in rear mech, i.e. nothing blocking its movement

Tried to reset from crash mode, but red LED does not flash even after holding button for 30 seconds. (Red/Green LEDs come on - as to change shifting option).

Removed battery and replaced with spare - same problem.

The only things not yet checked are

1) *rear mech connection to "in-frame" junction box. (I'll leave removing BB as a last resort, as I find it difficult to see how these connections could just work loose when protected in the frame)

2) E-tube / diagnostics - I don't have a machine running windows, (bike going into LBS tomorrow for diagnostics)

Has anyone experienced anything like this? A perfectly functioning Di2 rear mech, just failing for no obvious reason?

Any other suggestions welcome.

Thanks

BetterShifting_Terry

I'd say the problem is with either the wire from the shifter to Junction A, or the wire between the rear derailleur and the junction B, yeah...

Since the LED on the junction lights up OK, the connection between the Junction A - B - battery is OK.

My first step would be to connect it to a PC (even if it's only using the charger), to see whether or not the RD shows up. The fault can be with the shift lever too, of course.

Let us know what the guys at the bike shop find

mr_quiggs

Unfortunately it is the rear derailleur unit itself which has failed and needs replaced.
Luckily Shimano have them in stock, so should be back on the road early next week.

Munsford0

Ouch!