SB20 - Fixing Broken Shifters
A concern of many SB20 owners as their bikes age: Shifter buttons become erratic or stop working altogether.
Can the shifters be fixed? Yes, they can.
Who Should do this Work?
You should consider doing these repairs if your shifter buttons miss presses, produce double clicks or simply don't work.
Difficulty
If you are comfortable working with electronics, PCBs, SMDs, and perhaps like doing watch repairs, you have the necessary skills. I'll suggest the difficultly level for you is 7 out 10.
If you have never worked on small electronic devices or are uncomfortable working at sub-millimeter precision, the difficulty could be more like 11 out of 10 😳.
The good news: Misbehaving shifter buttons can be fixed to work better than new.
The bad news: Doing this work is not for everyone.
⚡️ Fixing a bad shifter can save an SB20 bike that would otherwise be headed for early retirement.
Tools and Supplies
Here's what's needed:
- Electronics contact cleaner (DeoxIT)
- Precision screwdriver / hex driver kit
- Tweezers
- X-Acto knife / Razor blades
- 5 mm hex wrench / key
- 3/32" (2.5 mm) drill bit
+ - Sheathing (vapour barrier) tape*
*Sheathing tape is what makes this repair viable! It holds the small membrane switches in place and ultimately makes repaired shifter buttons 100% sweat proof.
Related Posts
What About Zwift Click Wireless Shifters?
The Zwift Click (and Zwift Play) controllers can wirelessly change gears on a Zwift Hub and a few compatible trainers when using the Zwift app. They cannot shift gears on the SB20. The SB20 has hardwired shifters.
You can use these controllers to select menus and invoke features in Zwift. You just can't change SB20 virtual gears.
Fixing Malfunctioning Shifters
Overhauling your shifters will address the following issues:
1. Fix buttons that are no longer working
2. Improve shifting accuracy. No missed shifts. No unexpected double shifts.
Please review all the steps on this page before starting.
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First Up - Power Down
Unplug your bike before starting.
Removing Brake Lever Hoods
Push up from the bottom to lift off the brake hoods.
You can apply silicone spray to make removal easier.
Remove the handlebar tape to expose the remote buttons and brake levers.
Unfasten the 5 mm brake lever hex nuts.
Slide the brake levers (with attached remote buttons) off the handlebars.
Opening Shifters to Expose Membrane Switches
Brake Levers are opened by removing two 1.3 mm hex bolts.
You then remove the 4 Phillips screws that fasten the Button PCB to the Brake Levers.
You will be left with the switch assembly consisting of remote buttons, lever buttons and a wire harness.
Why Do These Switches fail?
Looking at the exposed membrane switches, you should be able to see the fundamental design weakness: Each membrane plate is held in place by a small piece of yellow translucent tape.
When exposed to sweat or moisture, this tape can loosen, causing the membrane to become misaligned and ultimately stop working. The membrane itself can also become mildly oxidized over time, causing missed or misread button presses.
Just Spray Them!
It is often suggested to spray contact cleaner into these switches.
While well intentioned, contact cleaner works as a solvent that causes the small pieces of tape to slip and fail prematurely.
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Building a Better Membrane Switch
The instructions below provide an easy way to build a more robust switch. The resulting assembly will stay aligned and have significantly higher moisture resistance.
The primary piece in the re-building puzzle is sheathing tape.
It is strong and moisture resistant. This tape sticks very well to hard surfaces, including PCB boards.
Switch Disassembly
Each switch is rebuilt by first disassembling and cleaning each component.
Ironically, you can start the process by spraying each switch membrane with contact cleaner 😇.
Alternatively, you can use isopropyl alcohol.
This will dissolve the tape adhesive, allowing you to lift off each membrane switch.
You can then clean each switch component.
Cleaning steps:
- Clean PCB contacts with contact cleaner.
- Remove membranes by soaking in alcohol and peeling off tape.
- Keep the white plastic frames for the rebuilding step.
- Thoroughly clean membranes with contact cleaner.
🛑 Startup Failures
You must be careful to avoid buttons that are inadvertently left in the pressed or 'on' position. The SB20 will not power up if a button is pressed when the power is turned on. There is no warning or external indicator. The bike just appears to be dead.
⚠️ You must align membranes carefully to ensure no buttons are pressed.
Rebuilding Lever Membranes
Rebuilding switches is a simple but delicate procedure.
Cut a small strip of sheathing tape. Trim it to be thinner than the membrane. This lets you to see the PCB contacts below when aligning the switch.
Place a white frame and membrane (reversed) on the tape strip.
Use tweezers to place the tape+membrane on the Button PCB. Carefully align the four legs on the membrane to sit squarely on the PCB contacts.
Take your time. You need sub-millimetre accuracy.
When you are satisfied with the contact-to-membrane position, press down firmly on the tape to secure the membrane to the Button PCB.
When you have replaced all membrane switches, take the Button PCB to your bike to test with the Stages Cycling app or GearView.
🔬 Test gear shifting for speed, feel and accuracy. Reposition the tape if needed.
👀 Right now, things may not look pretty or feel very robust. Hang in there. The next step provides the solution.
Securing Lever Switches
Here is the satisfying part!
Cut a large piece of sheathing tape large enough to cover both sides of the Button PCB.
Place the tape over all membranes at once.
Trim the tape as shown. Wrap the tape over to the back of the Button PCB. When done correctly, you will lock all membranes into position while creating a moisture seal around the entire Button PCB.
🔬 Take the complete switch assembly to your bike to test with the Stages Cycling app or GearView.
Rebuilding Remote Switch Membranes
Repeat the taping process with the Remote Switches.
Cut a large piece of sheathing tape to cover both sides of the Remote PCB.
Place the tape over both switch membranes at once.
Trim the tape as shown, Wrap the tape over to the back of the Remote PCB.
🔬 Take the switch assembly to your bike to test with the Stages Cycling app or GearView.
Completing the Brake Lever Buttons
Use a 3/32" (1.5mm) drill bit to restore the holes through the Button PCB.
You don't need a power drill. Just spin the bit with your fingers
Press the newly taped and sealed switch into the Button Shell.
Fasten the four Phillips screws to secure the Button PCB. Attach the Button Shell to the Brake Lever. Fasten the two 1.3 mm hex bolts.
✅ I added sheathing tape to the brake levers to further improve moisture resistance.
🔬 Take the reassembled brake lever to your bike one more time to test with the Stages Cycling app or GearView.
Assembling Remote Buttons
The remote buttons must be re-inserted into their rubber covers.
Apply a piece of sheathing tape to the underside of the cover to secure the buttons.
🔬 Take the reassembled remote buttons to your bike one final time to test with the Stages Cycling app or GearView.
Finishing up
Install the brake levers.
Move the the Remote Buttons to your preferred location.
🔬 I position buttons so they can be pressed by my index and middle fingers on the top bar.
Use sheathing tape to hold the buttons in place
Use electrical tape to help route the wires to the shifters.
Replace Hoods
Slide the hoods onto the brake levers.
Like the removal step: silicone spray makes hood installation easy.
🔬 You can postpone this step until after you have wrapped the handlebars.
(like I did in the picture above 😇).
Wrap Handlebars
You can now complete the job wrapping the handlebar tape. Here's how I do it:
Improved Buttons
You can also modify the physical buttons to further improve performance. Check out:
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FAQ
A: While it may look daunting, rebuilding the membrane switches is straight forward. You can even do it multiple times if something goes wrong. Removing tape requires only isopropyl alcohol and a pair of tweezers.
When the work is complete, your switches will work better.
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