The Shimano SM-EW90-A [paid link] junction box is a crucial component in Di2 electronic shifting systems, serving as the cockpit interface for shifters, wiring, and diagnostic connections. Over time, or after repeated bike servicing, its E-Tube cables may require replacement due to wear, damage, or upgrades to newer wiring. Correctly replacing and routing these cables ensures reliable shifting performance and maintains waterproof integrity. This guide provides a detailed, step-by-step approach for replacing the cable on your SM-EW90-A [paid link], covering preparation, installation, adjustment, and testing.
Tools Required
- Shimano TL-EW02 E-Tube tool
- Clean microfiber cloth
- Dielectric grease (Shimano approved)
- Isopropyl alcohol
- Workstand for stability
- Small flashlight or inspection light
Understanding the SM-EW90-A Junction Box
The SM-EW90-A is part of Shimano’s E-Tube Di2 system, typically mounted under the stem or integrated into the handlebar setup. It connects up to three E-Tube cables—two leading to shifters and one to the internal battery or frame junction (SM-JC41 [paid link]). Each port is precisely designed for waterproof E-Tube connections that transmit digital signals between Di2 components.
When replacing a cable, it’s essential to handle connectors carefully. E-Tube ports and plugs use friction-fit, sealed connections that can be damaged if removed incorrectly. Improper handling can lead to intermittent shifting failures or total communication loss.
Preparing for Cable Replacement
Before starting, shift the bike into a neutral gear and disconnect the battery (if external). This step prevents electrical shorting or damage to Di2 components. Clean the work area around the handlebar and junction box with a microfiber cloth to remove dirt or moisture.
Inspect the replacement E-Tube cable for bends, pinches, or kinks. The cable must be straight and undamaged to maintain waterproof performance and signal stability.
Removing the Existing Cable
To remove the cable, use the Shimano TL-EW02 tool. Insert the tool’s hook end behind the collar of the E-Tube connector on the SM-EW90-A port. Gently pull straight outward—never twist or bend the connector. Twisting can cause micro-fractures in the plug or socket, leading to unreliable data transmission.
If the cable feels stuck, check for debris or dried grease in the port. Do not use metal tools or excessive force. Once removed, inspect the port for dirt or corrosion. Clean the opening with isopropyl alcohol and allow it to dry completely before inserting the new cable.
Installing the New E-Tube Cable
Before connecting, lightly coat the new cable’s plug with a small amount of Shimano dielectric grease. This helps ensure a watertight seal and easier future removal.
Align the connector with the port—both are keyed to prevent incorrect insertion. Press the cable firmly until you feel a distinct click, indicating a proper seat. Avoid excessive pressure once it clicks into place. Improper seating may cause the system to fail to recognize the component during operation.
After installation, gently tug on the cable to verify a secure fit. Route the cable neatly along the handlebar or frame, ensuring it does not interfere with steering movement or brake housing.
Cable Routing and Strain Relief
Proper cable routing prevents tension and wear. The SM-EW90-A should have smooth cable curves with no sharp bends within 2 cm of the port. If mounted beneath the stem, leave a small service loop to accommodate handlebar rotation without stressing the connectors.
Use silicone E-Tube clips or adhesive mounts to secure the cable along the handlebar. Avoid electrical tape directly on the cable jacket, as it can leave residue and degrade the waterproof coating.
System Connection and Function Check
Once all cables are reinstalled, reconnect the Di2 battery. Press and hold the junction box button until the LED lights up to initiate system startup. Test the shifting through all gears. If any delay or non-response occurs, check each connection for full insertion.
Run a Shimano E-Tube Project diagnostic using the PC or mobile app. This confirms that all components communicate correctly and that firmware versions are compatible. If an error code appears, reseat the cable or inspect for damaged pins.
Troubleshooting Common Connection Issues
If the system fails to recognize the SM-EW90-A after replacement, disconnect the cable and inspect both plug ends. Dirt, water intrusion, or corrosion can disrupt the signal. Clean and reinsert using fresh dielectric grease.
If intermittent shifting persists, test the cable with another port or a different junction box to isolate the fault. Sometimes the issue lies with a damaged E-Tube socket or frayed cable from improper routing.
For persistent issues, check that the firmware of the junction box matches the rest of the Di2 system. Inconsistent firmware can prevent full functionality even with proper connections.
Optimizing Performance After Cable Replacement
After verifying functionality, optimize the cable layout to minimize movement during steering or vibration. Proper strain relief significantly increases cable longevity. Periodically inspect the junction box and cables for signs of wear or looseness, especially after wet rides or travel.
Applying a thin layer of dielectric grease during regular maintenance helps prevent corrosion and ensures long-term reliability. Additionally, keeping cables clean and free of debris reduces the risk of electrical interference or power loss within the system.
Compatibility and Upgrade Notes
The SM-EW90-A is compatible with all Shimano E-Tube Di2 systems (10- and 11-speed road setups) but limited to three connection ports. Riders upgrading to more complex configurations, such as additional shifters or accessories, should consider the SM-EW90-B [paid link] (five-port version).
E-Tube cables are cross-compatible across the Di2 platform, but ensure matching firmware and connector integrity. Mixing old and new generation cables may require system reconfiguration using the E-Tube Project software.
Final Verification and Safety Check
Before completing the service, verify the following:
- All cables are securely inserted and seated.
- Junction box is mounted firmly and correctly oriented.
- Steering rotation is smooth and unrestricted.
- Shifting response is instant and consistent across all gears.
After successful verification, clean the junction box and surrounding area, removing any grease residue. Proper installation and cable management will not only restore precise Di2 shifting but also extend the lifespan of both the SM-EW90-A and the E-Tube wiring system.
Replacing the cable on your Shimano SM-EW90-A is a straightforward yet precision-sensitive process. Attention to detail—especially with cable seating, routing, and waterproofing—ensures smooth electronic shifting and long-term reliability. Routine inspection and proper maintenance are essential to maintaining peak Di2 performance.