Installation Guide: Bar-end Junction EW-RS910

Updated August 5, 2022 by BetterShifting Terry

With the release of the DURA-ACE R9100 groupset Shimano also released a new Junction A - the EW-RS910 Junction. This is the junction box most people use on 11-speed Di2 bikes.

Installing it isn't as straightforward as installing the older below-the-stem junctions, but it's not hard - you just need to know what you're doing. This guide should clear things up a bit.

When you unbox the Junction you'll see all these bits and pieces:

EW-RS910 parts

On the top you see the four handle holders - two for each handlebar drop. These hold the junction and dummy end cap into place.

In case you're planning to install this junction into the frame instead, you'll need that mount pictured at top right and those two screws.

Also pictured are the dummy end cap, wire holder, a dummy wire and the junction itself.

Wire routing

This junction has only two ports, which can be a bit of a challenge when setting up your wire routing. A lot of people ask me how to convert their older below-the-stem junction setup to a bar-end junction one.

It is important to realise that Di2 itself does not really care how components are connected, or in what order. As long as components are connected, they will work.

The Shimano Way

Shimano mention a very specific wire routing in their dealer manuals. They connect the EW-RS910 Junction directly to the right shift lever. Then they connect left lever, EW-RS910 Junction and rest of the bike to each other using the EW-JC130 Y-splitter.

EW-RS910 wiring with EW-JC130

That blue box is the EW-WU111, the Di2 Wireless Module. You could also use the EW-JC200, which is just a "dumb" 2-port inline junction. You need a component there because the EW-JC130 Y-splitter is not long enough to run all the way to your Junction B. You need something to plug into the Y-splitter so that you can connect another, longer wire to it.

If you have to choose between the 2-port inline junction and the 2-port inline Wireless Module, prefer the Wireless module. It enables BluetoothLE / ANT communications for your Di2 bike, allowing you to connect it to your GPS bike computer and your mobile phone.

The alternative - without the Y-splitter

Now.. while the above method definitely has its advantages - more on that in a bit - it is also a bit chunky. Personally I prefer to not use the EW-JC130 Y-splitter for a much cleaner look.

This method involves chaining components together, perhaps best described using this wiring schematic:

Di2 setup without JC130

The left shifter connects to the right shifter, which in turn connects to the EW-RS910 handlebar junction. The second port on the junction is used to connect to the rest of the bike using a long electric wire (1000 - 1400mm).

I have also plugged the EW-WU111 Wireless Unit into the left shifter. Note that while it is an inline junction, you do not have to connect both ends.

Pros and Cons of each wiring setup

There are advantages and disadvantages to both setups, and which you choose is ultimately up to you. The main advantage of doing things the Shimano way is that you end up with two unused E-Tube ports, one on each shift lever.

This will let you connect two satellite shifters for example. Or two climbing shifters, or any other component.

Also, the Shimano way allows you to easily disconnect the front of the bike from the rest. This is really great when troubleshooting issues, or when changing handlebars for example - especially when running Di2 wiring and brake hoses internally.

Sounds good, right?

Here's the thing... it's rather bulky and ugly compared to the sleek lines of just running a single E-Tube wire into your frame.

I'm not the only one with this opinion, GPLama even did a video on removing the Y-splitter from his Di2 bikes.
(Full GPLama Di2 playlist here)

The disadvantage of cutting out the Y-splitter? You lose an E-Tube port. If you do this you'll be down to a single unused E-Tube port. This means you won't be able to connect multiple satellite shifters.

Personally I don't use any additional shifters, but this will be different for everyone.

Decide which one you like best and get your E-Tube wires routed through the handlebar. We can now get to the actual 'installation' part of this guide.

Installing the junction

Once you are satisfied with your wiring setup it's time to install the junction. This is relatively simple.

You take the wire holder, push the two wires exiting the handlebar through it and then connect them to the junction.

Now gently twist and push the junction into the handlebar. Yes, gently. Please do not use a hammer. The twisting motion helps the wire holder slide in properly.

Let's stick the end caps / holders on. Take half circle one, peel off the protective film and then stick it on the top. Next you'll take the full circle holder and place that over or on top of the other holder.

Confused? It's easy - this image will make things clear:

Yep, I have used a clamp to hold those pieces in place. The Shimano manual states that you should hold them in place for about one minute to let the adhesive do its job. I used a clamp and worked on the rest of the bike for a few minutes.

You do the same for the other bar-end - that is what the supplied dummy end cap is for. You do not have to use this dummy cap, of course. If you prefer to use a regular bar end plug then by all means do so.

Wrapping the handlebars

Finally, let's wrap the handlebar. If you're used to wrapping from top to bottom you're out of luck. EW-RS910 equipped handlebars are generally wrapped from the junction to the top.

This method is shown in Park Tool's "How to Wrap Handlebar Tape video at the 11 minute mark in their advanced techniques segment.

Also, depending on your handlebar, you may have a Di2 wire running externally. You'll wrap the bar tape over this of course, so you won't see a thing. However, some riders can easily feel this wire.
That's what the supplied dummy wire is for. I can be used in order to make both drops feel the same.

Secure the dummy wire to the handlebar drop using tape and then just wrap the bar tape over it. Now both drops should feel exactly the same.

Install the junction in the frame or seatpost.

Some frames have a special slot for the EW-RS910 junction. This is generally in the down tube, but could be anywhere. Specialized / S-Works like to put the junction in the seat post for example.

The specifics on how to install the juction in the frame itself are different for each brand. The dealer manuals are a good starting point and so is the frame manufacturer's documentation.

If you need any help or suggestions please don't hesitate to leave a comment or send an email - that's what the site is for!

BetterShifting Terry

About the Author - BetterShifting Terry

I enjoy playing with bike tech - both bike building and wheel building, bike maintenance and of course, Di2. Besides writing content and working on the technical side of BetterShifting, I also work as a Software Developer in The Netherlands. Read more on the About this site page.

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