rvtraveller

Did I find savings and a shortcut? I'm buying parts to replace the existing IGH transmissions on two bikes. The new stuff is Shimano Alfine IGH with Di2 shifting. My setup has only three electronic elements: gear indicator display/pushbutton shifter on handlebars, battery mount, and the shift motor. Shimano suggests I buy a simple four port junction box (no fancy button) and three separate wires to connect my devices together. However, I wonder if I could use the T-shaped wire harness (EW-JC130) they sell for connecting elements on Di2 derailleur bikes. That harness has three E-tube plugs, and I have three things to plug into. I've measured, so I know I have to splice some wire into one too-short branch, but otherwise everything lines-up. Savings would be $50 x2 bikes, and no blocky junction box to hide. I assume there is no magic to the junction box and it could be deleted as I suggest. Might this work?

Barry2 

That "junction box" contains flashable Firmware. I'm unsure as to why, but it appears to be more than a dumb "Y" connector.

Barry

rvtraveller

Hello, Barry. Thanks for your reply. The junction box I would use is the SM-JC41 (SM-JC40 as alternative). Unlike some Di2 junctions, the JC-41 and JC-40 have no buttons or any obvious function beyond tying the wires together. I don't understand why they would need circuitry in there.

rvtraveller

Moments ago, I found the reference below at bettershifting.com, so I'm still hopeful. Anyone else have thoughts?

"Junction A: The junction box at the front of the bike. Either below the stem, handlebar drops or the downtube. Usually a display on mountain bikes. Has a button, LEDs and a charging port.

Junction B: A “dumb” junction box that connects the rear (FD, RD, battery) to the front of the bike. Basically a 4 way splitter. SM-JC41 is the internal version, SM-JC40 the external one."

Iride01 

It'd probably help if you gave the Shimano part numbers of everything you are asking about. What some of us consider a Junction box might not be your idea of a junction box.

You have this? https://si.shimano.com/api/publish/s...001-12-ENG.pdf

It might not be for your model, but there are others available at https://si.shimano.com

rvtraveller

These are the parts to be connected:

MU-S705 - motor unit at IGH transmission

SM-BMR2 - mount for external battery

SC-S705 - gear indicator display (attaches independently to SW-S705 shifter switch)

The (dumb?) junction to be considered is SM-JC41. It has no buttons or lights. I think that junction is probably a simple splitter device.

The "T"-shaped EW-JC130-MM Shimano wire has three plug, and I have three devices to connect.

I've studied the manual that Iride01 linked. It led me to ask if that junction box was necessary.

Badger6

So the Y-cable you mention was specifically developed for drop bar bikes that use a bar end junction A, as opposed to the original style that is hung from the stem. In theory you could use the Y-cable. But, lets go back and review your set up...

Currently you need to get 3 items linked together. The most expeditious and easiest way is to use either a SM-JC40 (external) or SM-JC412 (internal) as Shimano describes in that manual you referenced above, and use 3 eTube wires EW-SD50 of the appropriate lengths to connect each component to the JC40/41 to build the system.

If you want to use the EW-JC130 Y-cable first you need ensure to get one long enough to at least get two of the components links, and you only need to worry about the end that is quite short at 50mm (about 2 inches). To extend that short cable end, you'd need to get an EW-JC200 junction and an EW-SD50 cable of the proper length to make that short end reach. No idea on the pricing, but in the end, it may not save you much, and it may be simpler to just build you system according to the diagrams in that manual you've already studied. Also, I've never heard of anyone using a Y-cable to do anything except connect an EW-RS910 junction box at a bar end.

Good luck!

rvtraveller

Thanks for your reply, Badger6. I can't auto-quote you here yet because I need to log more posts per the forum rules. But, I've copied your comments below my reply.

I've measured everything. The 550/50/550 (mm) version will serve the motor unit and battery mount perfectly. I'll need to lengthen one 550mm leg to reach the display/switch on the handlebars. I've confirmed there are only two wires inside the cable, so a secure and almost invisible splice is easy (for me). I have two-wire round cable of suitable dimension from years of cast-off A/C adapters and such. Cost savings would be at least $50.00 USD per bike. My wife and I have identical bikes, so $100 USD savings. I'm paying pandemic prices for these parts, so any savings are appreciated. My exterior wiring would be sleeker, too, without the junction.

[QUOTE BADGER6]

So the Y-cable you mention was specifically developed for drop bar bikes that use a bar end junction A, as opposed to the original style that is hung from the stem. In theory you could use the Y-cable. But, lets go back and review your set up...

Currently you need to get 3 items linked together. The most expeditious and easiest way is to use either a SM-JC40 (external) or SM-JC412 (internal) as Shimano describes in that manual you referenced above, and use 3 eTube wires EW-SD50 of the appropriate lengths to connect each component to the JC40/41 to build the system.

If you want to use the EW-JC130 Y-cable first you need ensure to get one long enough to at least get two of the components links, and you only need to worry about the end that is quite short at 50mm (about 2 inches). To extend that short cable end, you'd need to get an EW-JC200 junction and an EW-SD50 cable of the proper length to make that short end reach. No idea on the pricing, but in the end, it may not save you much, and it may be simpler to just build you system according to the diagrams in that manual you've already studied. Also, I've never heard of anyone using a Y-cable to do anything except connect an EW-RS910 junction box at a bar end.

Good luck!

[END QUOTE BADGER6]

Badger6

There are definitely some reports of folks splicing wires on the internets, but, it's an approach I wouldn't recommend. Reputable shops probably won't touch it after you do that, and Shimano will most certainly decline to honor any warranty. If you have further issues you'll be on your own, and probably right back here asking for help...please make sure you clearly state you modified the wiring harness/loom with splicing so we can then decline to offer any additional help because once the wiring is cut into, who knows. Sometimes saving a few pennies will ending up costing a few pounds. A lesson I've learned the hard way more than once because I am stubborn.

Troul 

I dont think the harness is truly waterproof, therefore, as long as the splices are done well I'd try it. if it has an IP rating of 67 or better, I'd opt to buying the harness.

rvtraveller

Reply to Troul:

Thanks for your reply The 3-plug harness is a Shimano part. It has the same connectors and cable as the straight wires, so I don't expect any more problems with water than using the more conventional parts. In fact, it reduces the number of connections from 6 to 3, so it should be more water resistant than the typical parts. My splice is easily waterproofed.

[QUOTE TROUL]

I don't think the harness is truly waterproof, therefore, as long as the splices are done well I'd try it. if it has an IP rating of 67 or better, I'd opt to buying the harness.

[END QUOTE TROUL]

rvtraveller

SPLICING THE WIRE HARNESS WORKED. Due to the bicycle parts shortage, it took me seven months to gather a mix of new and used parts (from five different countries) before I could build and install the Di2 Alfine wheel. This week I installed everything. Long story made short, there are very few components in an Alfine Di2 setup. Per my original post in this thread, I wanted to utilize one Shimano EW-JC130 Y-harness in place of three separate SD-50 wires and one dumb junction. This would mean splicing about 1 meter of new wire into one of the original branch wires. Di2 is a Canbus communication system with power and digital communications data (your shifting commands) being transmitted simultaneously on the same wires. THERE ARE ONLY TWO WIRES INSIDE THE SD-50 CABLE. Inside the black outer jacket are two insulated conductors (wires). One stranded wire has a red insulating jacket while the second stranded wire has a black insulating jacket. These are small gauge wires. I had to adjust my automatic wire strippers (already in the toolkit - $15) a few times to strip the outer jacket reliably, but the strippers worked well on the small insulated conductors (the small insulated conductors could be stripped with a thumbnail as necessary). Due to the very small wire gauge, a steady, experienced hand would be necessary to succeed with simple hand-operated wire strippers, but it can be done it that way. I wasted about 1.5" of SD-50 wire in adjusting the automatic wire strippers to cut the jacket, so do as I did and cut the original Shimano wire near it's middle, not near a plug: If you waste some original wire while stripping, you can add a few more inches of splice wire to compensate. I found a similar small diameter, two-conductor cable in my old parts bin. Like the Shimano wire, the junk wire had two insulated conductors within - one red and one black. If you need suitable wire to splice, your local thrift store will have lots of choices on their electrical adapters/chargers wall. The wire I used was from an old laptop charger cord. It matched well. I used heat shrink tubing to insulate each soldered conductor, then three layers of overlapping heat-shrink to stiffen and waterproof the area. To aid waterproofing, I didn't want the jointed area to flex, so pre-planned that it be at a place just zip-tied to the frame. Water-proof heat shrink tubing is readily available, but the regular stuff, well-applied, will work in my circumstances.
I'm can't teach joining wires in this forum. Experienced electronics people will have no trouble. Actually, joining and soldering these fine wires is pretty easy: Heat-shrink planning is harder! There are lots of resources on the web to demonstrate soldering wires. The most suitable soldering tool for this job is a simple fine-tip electric iron used for electronics ($20 anywhere). Avoid use of a high-powered pistol soldering gun on these fine wires and thin, melty, insulators. Now I will duplicate the work on my wife's bike. My total savings for both bikes together is now estimated at $120 USD. In addition, the wiring is neater, with no junction box to hide, and three connector plugs eliminated. As to warranty concerns, most of my parts are used or gray market (parts in non-retail packaging being offered for sale by bicycle manufacturers as surplus to their needs). As such, only the mechanical transmission is properly under warranty, and the local bicycle shop that sold the transmission and built my wheel will support me. Good luck.