Hacked di2 issue where not getting clean shifts

Discuss light weight issues concerning road bikes & parts.
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Joined: Thu Feb 07, 2013 7:45 pm

by bartturner

I purchased some of the DigiKey momentary switches, http://www.digikey.com/...t-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.
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. 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 to different bike.

Thanks for any help in advance!

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by xnavalav8r

Ultegra di2 and DA7970 are incompatible. Different programming, signals, software, and hardware. Had you tried this with the newer DA di2, I don't think you would have a problem. But I think the issue lies in the incompatibility of the two systems.

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by bartturner

Sorry if I confused. No I am not trying to mix the systems. I am using all 7970 stock parts except using the DigiKey momentary switches. I included talk of Ultegra DI2 only because the exact same switches did work with this setup without issue.

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by eliflap-scalpel

on 1st post , the link does not work

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by echtogammut

Honestly, I think a switch is switch so I doubt there is any kind of compatibility issue where it works with Ultegra but not Dura-Ace. I would get a multimeter and test the switch to see if there is an issue with the contacts. If I understand you correctly, you are splicing these switches in addition to the existing shifters, so if the existing shifters work then the switch should as well. My guess is the contact is not fully releasing after you depress the switch, a multimeter will verify this. Those Digikey buttons are ridiculously expensive, it would probably be cheaper to nab the remote buttons from something else and use those.

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by thisisatest

A switch is a switch on 7970. A switch is not a switch on 6770. You mention harvesting a little black box for the thing to function on the 6770 setup. Are you using it on the 7970 parts too? if so, leave it off, just use the basic switch.

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