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-   -   Brand new eTap group; *one* cog doesn't shift (https://www.bikeforums.net/bicycle-mechanics/1137476-brand-new-etap-group-one-cog-doesnt-shift.html)

Bob Ross 03-05-18 11:52 AM

Brand new eTap group; *one* cog doesn't shift
 
Just had a new SRAM eTap group installed on my 8-year-old Strong frame a little over a month ago. New chain, new cassette. Everything works wonderfully, very smooth, quick(enough), silent(enough) ...except for this *one* cog! Both when shifting up or shifting down, when it gets to this one cog it gets all hung up, either hesitates for too many (>5) seconds, or doesn't shift at all.

What could be causing this? The cogs on either side of this one aberration show absolutely no hesitation in either direction, so it doesn't seem like it could be a RD cable tension issue. [edit: duh, it's electronic, there aren't any cables!]

Could they have installed one cog backwards? (and would that even have this sort of effect?) Any other ideas? Thanks.

headasunder 03-05-18 12:18 PM

cogs cant be installed backwards take it back to the shop and get them to fix it.

Bob Ross 03-05-18 01:10 PM

Excellent suggestion, thanks!
But I was really asking more to learn what could possibly be causing this issue than simply looking for a quick fix that wouldn't teach me anything about what to root of the problem was.

Iride01 03-05-18 01:41 PM

Maybe a particular area the various joints the derailleur articulate on is a little rough, dirty or otherwise binds in such a way that it doesn't move freely at that point.

Can it be moved by hand so you can assess that? Or maybe take the chain off and see if you get an equal amount of travel from each shift and equal response time.

Marcus_Ti 03-05-18 06:23 PM


Originally Posted by Iride01 (Post 20206229)
Maybe a particular area the various joints the derailleur articulate on is a little rough, dirty or otherwise binds in such a way that it doesn't move freely at that point.

Can it be moved by hand so you can assess that? Or maybe take the chain off and see if you get an equal amount of travel from each shift and equal response time.

Check documentation before doing this.

IIRC Di2 documentation strongly advises against ever manually moving a Di2 derailleur's parallelogram.

Iride01 03-06-18 09:15 AM


Originally Posted by Marcus_Ti (Post 20206812)

Originally Posted by Iride01 (Post 20206229)
Can it be moved by hand so you can assess that?

Check documentation before doing this.

IIRC Di2 documentation strongly advises against ever manually moving a Di2 derailleur's parallelogram.

That's why I made it a question. I didn't know for certain. I probably should have been a little more verbose realizing that some wouldn't understand the meaning of why I wrote it as a question.

But thanks for clarifying it. I'd hate to know that others ruined their DR by not knowing the do's and don't's the manuals tell them.

TimothyH 03-06-18 09:57 AM

Always do the easy and cheap thing first.

Check bolts and fasteners including derailleur hanger to frame, derailleur to hanger and bolts on the derailleur itself holding the cage and pulleys together.

Check for play in the freewheel bearing. I had a bad freewheel bearing and it caused all kinds of missed shifts, skipping and hesitation. It takes a few minutes to check for side to side play.

Is the chain directional? Is it installed in the correct direction? Is it the correct chain? Try a new chain?

Is everything clean and lubed correctly? Battery fresh? Reboot the derailleur by removing the battery? Factory reset? I know little about E-Tap.

Getting to more time consuming diagnosis - Can you isolate the problem? Does the derailleur shift when it has no chain attached? Does it shift when the derailleur is completely disconnected from the bike? Does it only happen when the chain is connected? Does it happen in the stand with light hand power applied to the pedals or only when riding and full leg power is applied to the pedals? This might be one of the first things to try especially if the chain has a quick link and can be easily removed - take the chain off and see if the derailleur moves to the problem sprocket or not. If not then it is a problem with the derailleur and if so then it it may be a problem with either the drive train or the derailleur.





Originally Posted by Marcus_Ti (Post 20206812)
Check documentation before doing this.

IIRC Di2 documentation strongly advises against ever manually moving a Di2 derailleur's parallelogram.

Agree. Don't force the derailleur to move.


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