Where the wires converge.

The E-Tube Di2 Junction Box is what is referred to as the B Junction. This is the point in the wiring system where all the component pieces converge. It's a crucial item along with the five required wire sections to operate your Ultegra 6770, Ultegra 6870, or Dura-Ace 9070 Di2 shift system.

The E-Tube Di2 Junction Box is available in two configurations—Internal (SM-JC41) and External (SM-JC40). The Internal style is designed to be located inside the bike frame (usually inside the down tube, tucked in from a hollow bottom bracket shell). The External version is designed to be fixed on the outside of the bottom bracket shell, usually fastened to the cable guide.

Connects Di2 cycling component and battery wires
Available in external or internal configurations
Shimano's Di2 is the most popular electronic drivetrain in the pro ranks

Tech Specs

Crankset Compatibility

2 x 10

Compatible Components

Shimano Ultegra Di2

Recommended Use

ditching your mechanical tethers

Manufacturer Warranty

2 years

Size

Shimano

Di2 Reference Guide
Battery and Wires: Our Shimano Di2 packages are built for three standard configurations based on battery location and wire routing. First, you'll need to determine if your frame uses an internal or external battery mount, and whether the routing is either internal or external. Below is a guide for which battery, charger, mount, and junction boxes are required for your configuration.
Battery & Wire Configurations	Battery	Battery Charger	Battery Mount	Junction A	Junction B
External Battery with External Routing	SM-BTR1	SM-BCR1	SM-BMR2	SM-EW90 A/B 3/5 port	SM-JC40
External Battery with Internal Routing	SM-BTR1	SM-BCR1	SM-BMR2	SM-EW90 A/B 3/5 port	SM-JC41
Internal Battery with Internal Routing	SM-BTR2	SM-BCR2		SM-EW90 A/B 3/5 port	SM-JC41
Battery Mounts: The SM-BMR2 battery mount is available in three configurations -- Long External, Short External, and Long Internal. Both Long versions are to be mounted using the bottle cage mounts, while the Short version is designed for Di2-specific frames with either a chainstay or down tube mounting location.
Junctions: There are two junctions needed for completing your Di2 build -- A and B. Junction A, SM-EW90, is located at the handlebars and available in both three- and five-port options. The three-port option is intended for standard shifting with a left and right hand shifter. If you have the intention of using Shimano's satellite sprint shifters, or a combination of time trial shifters and shifter/brake levers, the five-port junction box will be the necessary selection. Depending on your frame specification, Junction B (SM-JC40 or SM-JC41) is located either internally or externally at the bottom bracket area. Accordingly, SM-JC41 is designed for frames with internal wire routing, while SM-JC40 is intended for external wiring options.
E-Tube Wires: For your convenience, we've created wire packages for your Di2 build kit in the sizes Small, Medium, and Large. Below, you'll find which wire lengths are included in each kit. Additionally, we've recommended a kit size based on your frame size.
E-Tube Wire Length Chart	S	M	L
Down Tube Wire	700mm	750mm	950mm
Front Derailleur Wire	300mm	350mm	400mm
Rear Derailleur Wire	500mm	550mm	600mm
Battery Wire	300mm	350mm	400mm
Note: E-Tube Wire Length Suggestions are an approximation.
E-Tube Wire Frame Size Guide	S	M	L
Frame Size	47 - 52cm	53 - 56cm	57cm+

Note:: This reference is meant to be used as a guide for creating a Shimano Di2 drivetrain package. For further assistance please feel free to give us a call.