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Shimano's Secret Black Box
article & images by Nick Salazar
Jul 11, 2013  hits 54,976

This unassuming little box is the secret to slick installations with e-tube Di2 groups.

I've said it plenty of times: Shimano's new E-tube platform for the Di2 component groups is the best thing that ever happened to electronic shifting. Not only did it bring improvements like smaller connectors, no-fuss waterproofing, and lighter weight, but it represents Shimano's commitment to keep the same wires for the foreseeable future. This means once you go through the relative headache of doing all the wiring, you can basically just upgrade the extremities of your drivetrain, leaving its nervous system intact.

Regrettably, the newest wiring junctions leave a bit to be desired in terms of minimalism. The big 3-port and 5-port junctions (part numbers SM-EW90-A and SM-EW90-B) are big and bulky, and don't do a good job of hiding out of the way like the original "Junction A" on the first-generation Di2 7970. Moreover, in snazzy little stem compartments like the one built into the Trek Speed Concept, and our own TriRig Sigma, the new boxes are too bulky to fit. Shimano, it seems, wants you to run them external, taking away the ridiculously-awesome aesthetic of a totally-hidden Di2 installation.

The 5-port junction box is a bit tricky to hide, since it doesn't fit in the Sigma or other stems like the Trek Speed Concept.

But fear not, dear readers. I've not only found out how to hide Di2 6770 and 9070 (the latest e-tube systems) within a TriRig Sigma stem, but basically bring back the minimalism of that original Di2 junction box, making it MUCH easier to make custom hidden Di2 setups on virtually any bike you like. Before we proceed, let's stipulate that getting into the nitty gritty of Di2, the component numbers, and frame modifications in general is not a topic for the faint of heart. Casual readers, you can jump overboard right now, because it's only going to get more geeky from here.

If you're still with us, of course, it means you want to know what's up with e-tube, and how to make it a bit sleeker. The answer is simpler than you think. It doesn't require any soldering, any electronics know-how, and involves nothing more than the clever use of one of the coolest little components in the e-tube universe. Hit the jump to find out why my favorite new bike part is a tiny black box known as SM-JC41.


Tags » custom,  di2group,  gadgets,  shimano
  • Shimano's SM-JC41 is designated as a rear junction, but we're going to show you how it can be used to even greater effect up front.
  • The Splitter Box consists of nothing more than four female e-tube ports. What's important is that the box doesn't care what you plug into those ports - it'll gracefully incorporate anything you throw at it into your Di2 installation.
  • Without custom wiring, this is basically the best you can do with the new Di2 junction boxes. They're a bit too bulky to fit inside the tiny little Sigma stem. Fortunately, there's a solution ...
  • The original Ultegra Di2 front junction, SM-EW67-A-E, is a perfect candidate for internal cable routing due to its small size.
  • Take a 67 Junction and add a pair of Splitter Boxes, and you've essentially created an 8-port front junction that stuffs easily into a frame or stem. Uh, sweet!
  • As you can see, the SM-JC41 Splitter Box is tiny. And at four grams, it's basically weightless. But its importance is huge.
  • Here's the inside of my Sigma stem before the cable cover gets bolted on.
  • When space is at a premium, you want to make sure any unnecessary elements are removed. Here, I shaved off the little zip tabs on the side of the 67 Junction, to save space inside the Sigma cavity.
  • And finally, we've landed. The 67 Junction is sitting inside the Sigma, perfectly visible and accessible. The rest of the setup is stuffed into the frame
  • All the Di2 cables come out the back of the Sigma and dive into the frame. This is very similar to how I have my Specialized Shiv wired up, although you can't see the cable entry because I hid it in the Shiv's built-in fairing. Maybe I should make something similar for the Felt.
  • Closeup on the 67 Junction, sitting happily in the Sigma stem.
  • This wiring is clean, simple, and looks great.
  • When was the last time you saw a Di2 installation that looked like this? With a little care and a TriRig Sigma stem., it's not that hard to achieve.
  • One more closeup on that front end.
  • And of course, this is why we go through the trouble. The wind sees nothing, except the frontal profile of the frame. We're going to rig this Felt B2 up with a TriRig Alpha bar in the near future. Stay tuned for the full review of the bike.

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