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Di2: Chain stays stuck in smallest cog after RD gets moved while bike is stationary ?

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Di2: Chain stays stuck in smallest cog after RD gets moved while bike is stationary ?

Old 05-10-21, 11:53 AM
  #1  
Bob Ross
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Di2: Chain stays stuck in smallest cog after RD gets moved while bike is stationary ?

Mystifying problem that's happened several times to my wife's 2018 Ultegra Di2-equipped bike:

She'll park it next to a curb with the drive side facing into the curb, and inadvertently push the rear derailleur cage against that curb. Or, it also happened when she's parked the bike in one of those bike racks that cradle the rear wheel; same deal though, the RD cage gets moved (pushed against the bike rack) while the bike is stationary.

When she then picks up her bike and starts to pedal it instantly upshifts into the smallest cog, and will not shift back up the cassette to any larger cogs.

This regardless of what cog or chainring she was in when she parked the bike.

The first time it happened and I was around I fidgeted with the RD, manually pushing it in towards the larger cogs while randomly hitting the upshift button on the right lever...eventually it miraculously though inexplicably righted itself.

She claimed it happened another time when I wasn't around, but by doing some equally unguided fidgeting was eventually able to get it to self-correct.

On yesterday's ride, it happened yet again -- yes, I finally read her the riot act about not parking her bike with the derailleur cage against any objects -- and no amount of fidgeting seemed to fix it. So she rode the last 10 miles in her small/small combination to the nearest bike shop. The mechanic there took it downstairs, and ~3 minutes later brought it back and said "You're all set."

I asked "What did you do to fix it?" and he essentially replied "I fidgeted with the RD, manually pushing it in towards the larger cogs while randomly hitting the upshift button on the right lever"

--------

Okay, so that's really not a satisfactory answer for me,,,nor a reliable solution should this ever happen again, especially if she's more that 10 miles from the nearest bike shop.

Anybody have an explanation for what exactly could be going on here, and what a more reliable (and Shimano factory-sanctioned) cure is?

Thanks.
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Old 05-10-21, 12:19 PM
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Sounds like crash mode enabled? Push the button on the junction box for 5 seconds or more until red light flashes. Then pedal the crank and the derailleur will cycle through the cassette and reset.
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Old 05-10-21, 12:37 PM
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Part of your story sounds like crash mode is getting engaged, but other parts sound like other stuff is going on.

Like a lot of things, if it's working now, what's to do?
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Old 05-10-21, 12:55 PM
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I would never push on the derailleur to fix it. I'd do what redcon1 posted...hold the button on the A junction til the red LED blinks, then pedal it. It will go to the large cog, then back down to the small cog. The LED will go out and you're ready to ride. I'd also have a shop plug it in to etube and run a diagnostic.
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Old 05-10-21, 01:13 PM
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Originally Posted by cxwrench View Post
I would never push on the derailleur to fix it. I'd do what redcon1 posted...hold the button on the A junction til the red LED blinks, then pedal it. It will go to the large cog, then back down to the small cog. The LED will go out and you're ready to ride. I'd also have a shop plug it in to etube and run a diagnostic.
Correct me if I am wrong....doesn't Shimano explicitly warn against manually moving Di2 RDs? That’s been stuck in my head for years now. Agree on taking it to a shop to be checked.

Last edited by Badger6; 05-10-21 at 01:35 PM. Reason: spelling...dammit Siri!
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Old 05-10-21, 01:18 PM
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Originally Posted by Bob Ross View Post
Or, it also happened when she's parked the bike in one of those bike racks that cradle the rear wheel; same deal though, the RD cage gets moved (pushed against the bike rack) while the bike is stationary.

Thanks.
They should have warning signs at the 9W Market (aka Filling Station) about this. Worst bike rack design ever.
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