Answered DI2 rear derailleur causes E8000 to switch off

[mxh]

I have a 2018 Merida e160 with the e8000 motor and Di2 shifting.

This morning a problem developed where pressing the up or down shift lever caused the power (motor, battery, display - everything) to switch off completely. It all switched back on OK, but as soon as I hit the shift lever (up or down) the power went off again.

Luckily my wife has the same bike, so I was able to do some testing, and have narrowed down the problem to the rear XT derailleur. If I plug the cable from my bike into her derailleur, all works OK (ie I can use my shifter to change gears on her derailleur). But if I plug the cable from her bike into my derailleur, her bike does the same thing - ie it power's off.

So now that I know that it's my derailleur that's at fault, is there anything more that I can do to try and fix the problem. Can I get to the electronics inside the derailleur? Is there anything that's serviceable / replaceable / fixable? Or am I just up for a new derailleur?

 

[urastus]

Try just having a look at the derailer - it might be something straight forward.

 

[mxh]

Try just having a look at the derailer - it might be something straight forward.

I was hoping for some ideas as to what the problem may be. Obviously I've looked at it, and from the outside it looks fine. I could try and take it to bits (although the tri-wing screws they use suggests they don't want you to), but I was hoping maybe someone else had had a similar issue, or maybe knows how serviceable (or not) these units are.

 

[R120]

Is the app showing any sort of fault? Or maybe this

 

[mxh]

Is the app showing any sort of fault? Or maybe this

The app shows that it recognises the derailleur is there, but doesn't show anything wrong. And even when in bluetooth mode, pressing the shift levers causes the power to go off.

Apparently some dealers have a diagnostics device for Di2 - I'll see if I can find one and ask them to test.

 

[Spiff]

There is a "Crash Protection" for DI2 derailleur, it is named "RD" and may turn off your bike after a crash. You can see it in one of the display menus, I am attaching how to reset it.

 

[mxh]

There is a "Crash Protection" for DI2 derailleur, it is named "RD" and may turn off your bike after a crash

Unfortunately that's not the problem. I tried doing the RD Protection Reset but as soon as I hit 'OK', everything just powers off.

It seems that any message sent to the derailleur gets a reply that causes the system to switch itself off.

Am taking it in for a diagnostics test tomorrow - will report back on the results.

 

[mxh]

So I took the bike and derailleur in to a shop with the diagnostics kit and they came to the same conclusion as me - it's broken!

I then checked with Shimano to ask about any repair service they offered. But apparently they only replace stuff under warranty - if it's out of warranty then tough luck, chuck it in the bin. Doesn't seem very 'green' - I thought there were laws about manufacturers having to be able to repair stuff for a certain period of time (5 or 10 years), but maybe that's only fridges!

So the bottom line is I had to fork out $500 for a new derailleur. Although there were a couple of silver linings - 1) after a week or so, it went into Crash Protection mode after a DH run which might previously had me pushing back up the hill with the bike stuck in 11th gear as I used to have no idea what this feature was, but with my new-found knowledge I was able to reset it and get going again. And 2) I managed to bend part of the derailleur (not the hanger, but the bit that connects to the hanger), but instead of having to try and bend it straight, I was able to just take this bit of my broken derailleur!

 

[Spiff]

DI2 Derailleurs are serviceable, Shimano has Exploded Part List and parts can be bought, I did. This is the one for my RD-M8050 derailleur

 

[mxh]

DI2 Derailleurs are serviceable, Shimano has Exploded Part List and parts can be bought, I did. This is the one for my RD-M8050 derailleur

Well, they are serviceable if it's not an electrical issue, as my problem was.

As you can see from your Exploded Part List, the bit that contains the electrics is the central bit that all the spare parts are bolted to. So for my problem, the only option was to buy a new derailleur.