The Shimano SM-EW90-B [paid link] Junction A is one of the most critical components in any Di2 (Digital Integrated Intelligence) system. It acts as the central connection hub for the front wiring, linking the shifters, derailleurs, and battery through the E-Tube network. Despite its compact design and straightforward function, incorrect installation of the SM-EW90-B [paid link] can lead to severe shifting issues, intermittent power failures, or complete system shutdown. This guide covers common installation mistakes, explains why they happen, and provides precise methods to ensure a flawless setup.
Understanding the Shimano SM-EW90-B Junction A
The SM-EW90-B is a handlebar-mounted Di2 junction box with three E-Tube ports, typically used in dual-control lever setups. It manages data communication and power distribution between the front and rear derailleurs, the battery, and the shifters.
Its role is central: any error during installation—such as a poorly seated connector, incorrect cable routing, or electrical contamination—can compromise the performance of the entire Di2 system. Therefore, a meticulous installation process is essential for reliability and long-term durability.
Tools Required
Before starting, prepare the following tools and materials:
- 2mm hex wrench
- Shimano TL-EW02 E-Tube connection tool
- Electrical contact cleaner
- Microfiber cloth
- Isopropyl alcohol (for degreasing)
- Shimano E-Tube compatible cables
Incorrect Cable Insertion
One of the most common and costly mistakes is forcing E-Tube cables into the SM-EW90-B ports without using the Shimano TL-EW02 tool. Each E-Tube port is designed with precision tolerances to ensure waterproof sealing and data continuity.
When the cable is inserted incorrectly or with excessive force, the delicate internal seals can become damaged. This damage often results in intermittent signal loss, random shifting, or complete communication failure.
Always insert cables using the TL-EW02 tool, pushing straight into the port until you feel a firm click. Avoid twisting or bending the cable during insertion. Equally important, never pull the cable out by hand—use the tool to safely release it without stressing the connector housing.
Mounting in an Improper Position
The SM-EW90-B is designed for mounting beneath the stem or on the handlebar. However, placing it in a location where cables bend sharply or face direct exposure to sweat and moisture can lead to corrosion and stress fractures.
When installed too close to the stem faceplate bolts or under tight bar tape, the E-Tube cables may be forced into unnatural angles. Over time, this causes micro-cracks in the insulation and data transmission errors.
To avoid this, mount the junction box in a position that allows smooth cable curvature with minimal stress. Ensure the ports face downward or backward to minimize exposure to sweat and rain ingress.
Skipping the Cable Inspection
Even new E-Tube cables can develop minor imperfections during routing. Tiny kinks, especially near the connector ends, can cause erratic shifting behavior that’s difficult to diagnose.
During installation, inspect each cable end under proper lighting. If a connector shows signs of bending or dirt contamination, clean it with isopropyl alcohol and a lint-free cloth. Replace cables showing visible damage or resistance when inserted.
Never reuse cables that have been sharply bent or pinched during removal; internal wire fractures are invisible and can cause system instability.
Ignoring Firmware Compatibility
The SM-EW90-B must operate on compatible firmware with the rest of the Di2 system. Installing an older junction box with updated derailleurs or shifters without performing a firmware update can cause system communication failures.
Use Shimano’s E-Tube Project software to verify firmware versions before installation. If components are mismatched, update the firmware using the SM-BCR2 charger/PC interface. This step ensures all connected parts communicate efficiently under the same data protocol.
Skipping this step can make the junction box unresponsive or cause one of the derailleurs to stop functioning mid-ride.
Not Securing the Junction Box Properly
The SM-EW90-B relies on friction or a dedicated mounting clip for stability. A loosely installed junction box can rotate or shift during riding, putting strain on the connected cables.
Over time, this movement causes gradual disconnection or water ingress. The box should be positioned firmly, with cables aligned naturally and without tension. When mounting under the stem, ensure there’s sufficient clearance for turning the handlebars without pulling on the cables.
Avoid using adhesive tapes or zip ties as substitutes for the factory mount, as these can trap moisture or damage the port seals.
Overlooking Moisture Protection
Although the SM-EW90-B is designed to be weather-resistant, improper sealing at the cable entry points can lead to moisture intrusion. Sweat, rain, and washing detergents can corrode internal contacts, causing the system to power off intermittently.
To prevent this, confirm that every cable is fully inserted until the click is felt. For riders frequently in wet environments, applying a minimal amount of dielectric grease around the outer cable seals can enhance long-term protection without compromising electrical contact.
Forgetting to Test After Installation
After installation, many mechanics neglect to perform a full diagnostic test using Shimano’s E-Tube Project software. This test checks communication across all connected devices, ensuring no ports are inactive or shorted.
Skipping this verification can leave latent issues unnoticed until the system fails during a ride. Always connect the Di2 system to the E-Tube software to verify correct communication, firmware synchronization, and power continuity.
Once confirmed, test shifting under static and dynamic conditions to ensure smooth, instantaneous gear changes across all derailleurs.
Cable Length Errors
Using cables that are too short or excessively long creates unnecessary stress and clutter. Short cables pull on the junction box during steering, while long cables increase the risk of entanglement and signal noise.
Each bike frame geometry requires precise measurement. Shimano recommends maintaining gentle cable loops with a minimum radius of 25mm. Cutting corners on cable planning can compromise not just the SM-EW90-B, but the entire Di2 wiring integrity.
Final Quality Check
Before completing the setup, inspect the junction box alignment and cable routing from multiple angles. Confirm that no cables are pinched under the handlebar tape, and that each connector is fully seated.
Power up the system, shift through all gears, and ensure LED indicators on the SM-EW90-B respond correctly. A green LED signifies proper operation, while flashing red or no light indicates a connection or firmware issue requiring further inspection.
Conclusion
Proper installation of the Shimano SM-EW90-B is essential for reliable Di2 performance. Most issues stem from cable handling errors, poor positioning, or neglected firmware updates. Taking the time to mount the junction box correctly, inspect every connection, and verify system communication ensures seamless shifting and long-term electrical reliability. By avoiding these common mistakes, you protect both your investment and your riding experience.