The current installation (performed by the supplier) of the junction-box (EW-RS910) results in only one port left at the levers for what's usually used for sprint or climbing shifters. This port is found at the left lever (ST-R8050 L).

Can I get Shimano's four-port junction-box (SM-JC41), plug in the aerobar shifters (SW-R9160), and connect one of the remaining two ports of the junction-box with a wire (EW-SD50) to the available port on the left lever and thereby make it work?

Is there a better way, even if it works?

2 Answers 2


Yes, you can. You can have as many SM-JC41s as you like. It's basically just a 'dumb' connection box.

Each shifter has 3 ports, so are you really in need of more ports? I think your current setup is:

Left shifter => EW-JC130 => right shifter
EW-JC130 => Junction A (EW-RS910)

That would mean you still have 4 ports available, right? (2 per shifter)

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A climbing shifter usually only takes up one port, but I suppose if you want to add sprint shifters you might need two free ports.

Note that you can have only one of the Junction A boxes (EW-RS910, SM-EW90-A/B) as the Shimano compatibility charts state: https://e-tubeproject.shimano.com/pdf/en/HM-CC.3.4.0-00-EN.pdf

Also note: max 6 shifters.

The B junction is not mentioned(just like EW-JC130 and EW-JC200) because they're just connectors and you can have as many as you like ;)

I'm not sure what the best setup would be, but think that is your only option if you want to connect that many devices.


One very important point to add to the above post -

The original poster asked about aerobar shifters. These are different from the sprit shifter in that they cannot go into the bottom sprint shift ports. And a junction box B will not be seen from those ports. This is a little strange - I expected they would be treated just like a sprint shifter - but the Shimano documentation makes it clear that even the single button aerobar shifters have to tie into one of the top two shifter ports - which can include a JC41-B on the way.

The way I set this up was to have my two aerobar shifters enter a 4-port JC41-B. Then one of the remaining JC41-B ports goes back to the junction B under my crank towards the battery. The last JC41-B port goes to the left shifter in one of the top two positions. Then the remaining top position on the left shifter runs across to connect to the right shifter, and the second remaining top position on the right shifter goes down to a bar-end junction A.

This let me mount the JC41-B right under my stem which lets me quick release and electrically disconnect my redshift aerobars in seconds while having the benefit of Di2 bar end shifters whenever I have them on.

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