# Di2 rear derailleur won't stay in largest gear?



## BobDobalina

Hey there, just got my first bike with electronic shifting (Specialized Roubaix) and I'm loving it, except for one thing: it won't stay in the largest gear. It'll go down to that gear, but about 5 seconds later it pops back to the next-largest. 

I thought it was just an alignment issue so I did the microadjustment, but still had the same issue. I then watched the mechanism more closely and realized that it's not an alignment thing, the derailleur is actually shifting back after five seconds or so.

Very strange and I'm a bit stumped. Would normally run down to my LBS but... yeah. Quarantine.

Appreciate any suggestions.


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## tlg

It sounds like the limit is set wrong.

Is your LBS closed? Most are allowed to remain open for service.


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## BobDobalina

Thanks for the reply. They're open but limited hours and it's a bit of a process of scheduling an appointment, leaving the bike, coming back later, etc. And it's a bit of a drive. And frankly I'm doing my damndest to keep human interaction to a minimum. 

Is this just a matter of adjusting the limit screws like on a traditional derailleur?


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## tlg

BobDobalina said:


> Thanks for the reply. They're open but limited hours and it's a bit of a process of scheduling an appointment, leaving the bike, coming back later, etc. And it's a bit of a drive. And frankly I'm doing my damndest to keep human interaction to a minimum.


Gotcha. Yea can be a bit of a hassle. Plus, always better to be able to do it yourself.



> Is this just a matter of adjusting the limit screws like on a traditional derailleur?


Yes, more or less.

Page 129 of the Manual
https://si.shimano.com/pdfs/dm/DM-R8050-02-ENG.pdf


This is a really good site for Di2 info.
This page is pretty much copied from the Di2 manual in an easy to follow guide.
https://di2center.com/2019/04/25/how-to-micro-adjust-your-road-bike-di2-rear-derailleur/


Older Di2 but essentially the same.


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## BobDobalina

Thanks very much, sounds like the overshift feature he mentions in the video may be what I'm seeing. I was confused why it would shift into gear then shift out again. Will give that a shot. Thanks!


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## tlg

BobDobalina said:


> Thanks very much, sounds like the overshift feature he mentions in the video may be what I'm seeing.


Yes, that's exactly what it sounded like to me too.

I had it happen once, but it was on the large cog. What a b!tch going up a steep hill and it keeps shifting back after a few seconds.


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## Peter Kettle

Page 133 of that Shimano manual exactly describes the symptoms "... the gear may shift back by one gear after about 5 seconds". I adjusted the low-side stopper bolt as instructed (half a turn), problem fixed.

Thank-you


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## Kfarley3333

This was exactly my problem and sure enough a half turn sufficed to prevent the motor sensing the stop 👍


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