# Di2 noob - need help diagnosing a problem



## HISI808 (Dec 25, 2012)

Just got a new bike with Ultegra Di2 6870.

I have a 11-28 cassette. Whenever I shift to the 28 cog, either in small (34/28)/big (50/28 I know cross-chaining is bad) chainring it shifts, but then after a few seconds, it automatically drops down to the next cog which is the 25.

Do I need to adjust the front or rear deraillieur? Or is it something else? Can I use the E-tube software to do this?

Thanks in advance!


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## J.R. (Sep 14, 2009)

Is there a chance that it's running against the limit screw?

See here: https://docs.google.com/file/d/0B61...Q1Yy00YzEwLTlmMjgtNzIzMjYxNjBlMmRj/edit?pli=1 page 59 for rear limit adjustments.


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## goodboyr (Apr 19, 2006)

Or rear hanger could be misaligned.


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## rcb78 (Jun 15, 2008)

It's the low limit screw. If it's set too tight, the derailleur backs down a cog after a second or two. You should only 'just' be making contact with the low limit screw when the derailleur is in the lowest gear.


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## HISI808 (Dec 25, 2012)

J.R. said:


> Is there a chance that it's running against the limit screw?
> 
> See here: https://docs.google.com/file/d/0B61...Q1Yy00YzEwLTlmMjgtNzIzMjYxNjBlMmRj/edit?pli=1 page 59 for rear limit adjustments.


This did the trick. Backed off the low adjustment bolt and then retightened until it just touched the stopper.

thanks guys for your help. Saved me a trip to the bike shop. :thumbsup:


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