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Hacked di2 issue where not getting clean shifts

Discussion on bikes, and whatever...

Hacked di2 issue where not getting clean shifts

Postby bartturner » Fri Apr 12, 2013 5:58 pm

I purchased some of the DigiKey momentary switches, http://www.digikey.com/product-detail/en/MTG72AD2 I originally used with Ultegra Di2 and they worked without a problem on my P4.

I recently purchased a P5 and built the bike with Di2 7970 and used the DigiKey switches. Everything is stock besides the cable splices on the front wire harness and the Digikey switches. The problem is that I can not get clean shifting in the rear. The shift will happen but not stop. The rear derailleur will continue to engage on it's own and make additional, random, shifts. I can hear it continue to engage when the Digikey switch is in an open position.

I am curious if anyone has run into this problem. I have not done much debugging on this yet. It is only a problem on the rear and not the front. It seems to me it could be a couple of problems

1) There is a short of some kind in my wiring causing the issue. I think this is most likely. But I have done many, many wire splices and never had a problem before.
2) These momentary switches work find with Ultegra Di2 but are not compatible with the old (7970) Dura Ace. The thinking being that the little black boxes that I harvested cleanup the signal from these switches to only send one shift to the rear derailleur with Ultegra di2. With 7970 the boxes are not used and the Digikey switches are not sending clear momentary switch. Or maybe the Digikey switch has gone bad.
3) The rear derailleur is defective. I actually believe this to be the most unlikely but you never know.

I am curious if anyone else has ever run into this issue? Any tips appreciated.

What I plan on doing

1) Disconnect the DigiKey switches and manually short the wires and see what happens with shifting. If this fixes it I plan on swapping the front and rear Digikey shifters and see if this helps. If this does not help then undo my wire splices and try the same thing with the wires directly out of the front wire harness. If still have issue with wires directly out of the front wire harness then I have a tough decision. Either replace everything with stock so purchase the Shimano front shifters and a new front wire harness that has not had the wires cut. See if it now works. Or just replace the rear derallieur. Thoughts?

2) The other option is just replace the 7970 with my Ultegra Di2 which I am not really using. But this would require me to re-cable the bike. Move the 7970 di2 to different bike. Kick the can up the road on actually fixing what is wrong with my 7970.

Thanks for any help in advance!
bartturner
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