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Di2 Ultegra Cabling Arcanery: No Junction B?

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Di2 Ultegra Cabling Arcanery: No Junction B?

Old 01-08-17, 07:52 PM
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Di2 Ultegra Cabling Arcanery: No Junction B?

I think this might be possible...LBS isn't so sure, having only built a handful of Di2 rigs...So I yield to you all...I'm plotting a build that would need external cabling, catch being using cabling would be CX style along TT (long story but informative as to whys of frameset choice). Using Di2 hydro R785 shifters and Ultegra RD/FD with seat tube battery.

Per the header, I'm wondering if it is possible to run Di2 Ultegra with no Junction B. Topology (routing) would in my hair-brained mind, after an 8% ABV Paulaner Salvator, look like this:


R785L _________R785R
\_____________/
(5-port Junction A)
____/____|_______\
wireless__FD______RD
|
Battery


Alternatively sans D-Fly wireless unit like so

R785L _________R785R
\_____________/
(5-port Junction A)
____/____|_______\
battery__FD______RD


Sorry for formatting, BF hates my ASCII diagram. IOW, using the 5-port JunctionA as the only breakout I need. I've read about MTB Shimano XT Di2 not needing a Junction-B...and read that both the internal and external Junction B boxes for Ultegra Di2 are just "dumb" port breakout boxes. Further removing the Junction-B would tidy things up quite a bit on the frameset. Thus the question.

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Old 01-08-17, 08:19 PM
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Interesting, just for clarity, are you talking about using an EW90-B ?

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Old 01-08-17, 08:27 PM
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Originally Posted by jbucky1
Interesting, just for clarity, are you talking about using an EW90-B ?

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Sorry, correct!

To avoid confusing myself with SKU gibberish, I was using english-like names
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Old 01-08-17, 08:36 PM
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Yep it will work then. Im not sure on your set up but you may encounter issues getting the correct setup with specific lengths of e-tube wires.
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Old 01-08-17, 08:56 PM
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Originally Posted by jbucky1
Yep it will work then. Im not sure on your set up but you may encounter issues getting the correct setup with specific lengths of e-tube wires.
Excellent. From some rough initial guesstimating a 1400mm cable can feed the RD with maybe 12cm of slack to spare. It is somewhat theoretical until Rodeo releases the final frame measurements.

I do have some time before building (probably 2-3 months)....so maybe SRAM eTap HRD will be public by then and not 50% more expensive than Ultegra Di2 Hydro (like MSRP suggests), and have better brakes than the lackluster praise I've read so far.....but I'd rather Di2 anyway.
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Old 01-08-17, 10:23 PM
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Shimano kind of mucks things up with A and B junction and then having SKU for the A junction with A and B attached to the SKU.
The A junctions are the ones with the button and LED lights and are required, though the XTR series has one with a readout for
the chain position on the CW and cassette (which works for road setups equally well).

The SM-JC40/41 junctions are just 4 in 1 paralleled connex meant to be near the BB for receiving the wire from the handlebars,
and to the battery/RD/FD. Doing it your way means running 3 wires up to the A junction from the BB area, could be a bit messy
compared to the usual one wire from the A junction down to the BB area with a dumb B SM-JC40 junction.
Simplify things with a BB area external SM-JC40 junction under the BB it will work better or at least be a lot cleaner, even assuming you can
find a wire long enough to go from the RD to the A junction.
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Old 01-08-17, 10:44 PM
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Originally Posted by sch
Shimano kind of mucks things up with A and B junction and then having SKU for the A junction with A and B attached to the SKU.
The A junctions are the ones with the button and LED lights and are required, though the XTR series has one with a readout for
the chain position on the CW and cassette (which works for road setups equally well).

The SM-JC40/41 junctions are just 4 in 1 paralleled connex meant to be near the BB for receiving the wire from the handlebars,
and to the battery/RD/FD. Doing it your way means running 3 wires up to the A junction from the BB area, could be a bit messy
compared to the usual one wire from the A junction down to the BB area with a dumb B SM-JC40 junction.
Simplify things with a BB area external SM-JC40 junction under the BB it will work better or at least be a lot cleaner, even assuming you can
find a wire long enough to go from the RD to the A junction.

Thing is, this is a CX frameset. Toptube cable routing. So I'm not even certain there's hardware for a BB junction mount on the BB shell even if I wanted to use it.**

**Further to use a BB JctB requires as long if not longer cables. Since, due to CX stops, I'd need to go JctA--across top tube----down seat tube---JctB. And being CX routing, the cable stops for RD are on the seat stay not the chain stay. So running a standard Di2 routing to RD would require zip tie city. And zip-tie city is a sure way to ugly up a purdy bike....and if it came to that I'd almost be tempted to pay 2X as much for eTap HRD ($2900 versus $1800).


All of those headaches can just be avoided by not using a JctB box at all....or if worse came to worse, jerry rigging a JctB near the seat tube cluster. All cables would go down the top face of the top tube.

If still confused...check this link and look for frame pics, The black points on the frame are for cable routing.: https://www.rodeo-labs.com/the-labora...al-background/

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Old 01-09-17, 10:43 AM
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Looked at the website, new Ti CX frame, beautiful bike. I am partial to Ti, with a decommissioned Teledyne Titan, an actively used
Lightspeed Vortex (2001) and same vintage Ti Rotator Pursuit bent, recently converted to rear RD Di2 10spd. Unless Rodeo is helpful
with frame piercings, I don't see how you can avoid three wires on the top tube to the bars, as the RD/FD/Battery all have only one
plug each. How does Rodeo get the seat tube battery wire out? Hopefully Rodeo will realize they need to plan ahead for wired
shifting with appropriate frame perforations, or they may just assume wireless is the future, which it probably is. eTap is so clean
by contrast. Had external wiring on the Vortex for a while and when the Titan cracked a chainstay, I had to get a new frame, the
cheapest was a CF with internal routing that was a natural for a 10 -> 11 spd Di2 conversion with the takeoffs being used on the bent.

The Lightspd frame was really filthy with all the external wires when taken down, they are really grunge collectors.
Dunnoh what your budget is but the eTap HRD looks REALLY attractive by comparison. Still puzzling over how the seat tube battery wire
the Rodeo would be accessed....
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Old 01-09-17, 11:20 AM
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Originally Posted by sch
Looked at the website, new Ti CX frame, beautiful bike. I am partial to Ti, with a decommissioned Teledyne Titan, an actively used
Lightspeed Vortex (2001) and same vintage Ti Rotator Pursuit bent, recently converted to rear RD Di2 10spd. Unless Rodeo is helpful
with frame piercings, I don't see how you can avoid three wires on the top tube to the bars, as the RD/FD/Battery all have only one
plug each. How does Rodeo get the seat tube battery wire out? Hopefully Rodeo will realize they need to plan ahead for wired
shifting with appropriate frame perforations, or they may just assume wireless is the future, which it probably is. eTap is so clean
by contrast. Had external wiring on the Vortex for a while and when the Titan cracked a chainstay, I had to get a new frame, the
cheapest was a CF with internal routing that was a natural for a 10 -> 11 spd Di2 conversion with the takeoffs being used on the bent.

The Lightspd frame was really filthy with all the external wires when taken down, they are really grunge collectors.
Dunnoh what your budget is but the eTap HRD looks REALLY attractive by comparison. Still puzzling over how the seat tube battery wire
the Rodeo would be accessed....

Yea the seattube battery is a problem. Already talked to Rodeo about that bit, and Steve @Rodeo is talking to their engineers about it. One alternative is steerer-mounted battery, which Shimano even makes a mounting for. Another one is Custom fabbing a seatpost with a hole for a grommet and wire in it.

The cabling along the TT is all but unavoidable and between cable fixtures and Shimano covers, I think I can deal with it and be happy.


eTap HRD is its own problem....the discs aren't well thought of in the few public reviews compared to the glowing ones of Di2 hydro. Which when factoring in the price inflation makes me less enthused about it....also don't know when it will be available, as of now it isn't AFAIK.
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Old 01-09-17, 11:00 PM
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Googled up the steerer tube mount: looks like a better idea than the seat post mount and
obviates one top tube wire. One writeup makes it generally clear: Shimano XTR Di2 installing the battery in the fork steerer - bikeandskiblogbikeandskiblog
Only question is what is minimum length the steerer can be to take the battery.
Looks like a solution.

My first Di2 build was in 2013, limited access to wires so had to deal with lots of extra
wire length, hence part of reason for grunge collection. Now there is ready availability
of any length of wire for reasonable prices (~$20 from Jensen or others) so install can
be cleaner.
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Old 01-09-17, 11:32 PM
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Originally Posted by sch
Googled up the steerer tube mount: looks like a better idea than the seat post mount and
obviates one top tube wire. One writeup makes it generally clear: Shimano XTR Di2 installing the battery in the fork steerer - bikeandskiblogbikeandskiblog
Only question is what is minimum length the steerer can be to take the battery.
Looks like a solution.

My first Di2 build was in 2013, limited access to wires so had to deal with lots of extra
wire length, hence part of reason for grunge collection. Now there is ready availability
of any length of wire for reasonable prices (~$20 from Jensen or others) so install can
be cleaner.
AFAIK the seatpost-format batteries are about 16CM long. Which for me on a 56CM frame should come out very close to working depending on how headtube height works out and steerer length. Shimano also has a stem designed for fishing Di2 cabling through it on the MTB end...

Tested: PRO Tharsis Trail Di2 Cockpit ? Flow Mountain Bike
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Old 01-09-17, 11:43 PM
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Love that headtube install. Nice writeups

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