Logitech MX Master 3/3S: Cleaning the scroll wheel assembly to fix broken SmartShift and Free Scroll

[TarasBuria Reporter]

My good-old MX Master 3 I pimped with silent switches started to show its age (bought in Dec 2020): SmartShift stopped working, and the free flow scroll would halt almost immediately. I decided to try cleaning the wheel assembly to see if it could save my beloved mouse from landfill.

Also, I did not want to buy the MX Master 3S since it uses the Bolt connector, and my MX Keys keyboard uses Unifying. Upgrading the keyboard was not an option—it still works almost flawlessly, except for the smart backlight, which often goes haywire (not a big deal).

What you will need:

1. A new set of glides. Screws are hidden under (above?) the glides (feet), so you need to remove them. Technically, you can recycle them with double-sided tape, but I suggest buying a new set from iFixit or a third-party alternative. My local shop sells amazing glides that are much better than stock.
2. PH000 and T4 screwdrivers
3. A brush
4. Steady hands (optional)

Off we go:

1. Turn off the mouse.
2. Remove the side and bottom feet. You can keep the upper one (below the T4 screw) — there is nothing under (above?) it.
   
   
    
3. Carefully detach the upper shell—a ribbon cable connects its bits to the main board; do not rip it off.
4. Disconnect the battery cable. It's not required, but you better do it for your mouse's safety.
5. Disconnect the three-wire cable and the ribbon coming from the wheel assembly.
   
   
    
6. Unscrew two PH000 screws keeping the wheel assembly in place.
   
   
    
7. Remove the wheel assembly. Important: pay attention to the small spring sticking from the bottom of the assembly. It is there to ensure a smooth middle click. Do not lose it!
   
   
    
8. You can keep the small PCB attached to the assembly, but I recommend removing it to avoid accidental damage.
9. Find a small blob of glue that keeps the power connector (three-wire cable) attached to the actuator. Grab tweezers or use your fingernails (if you have such) to remove it. It should not hold too tight. I think there is no need for glue since the connector sits tight enough.
   
   
    
10. Now, you can disconnect the cable from the wheel actuator.
11. Grab something tin and slide it under the wheel shaft on the other side. Push it up to dislocate the wheel.
    
    
     
12. Carefully pull the clip near the actuator connector (next to two copper pins) and remove the wheel from its plastic housing. Pull sideways just a little to avoid breaking the clip. Also, be careful with thin copper wires coming from the actuator.
    
    
     
13. Clean the housing. That yummy substance was the culprit.
    
    
     
14. You can also remove the actuator from the wheel to see if it needs extra cleaning. Also, you can admire the fine work and the wheel's heft.
    
    
     
15. Once everything is clean, put the wheel inside the housing and slightly push the wheel down until you hear a click. Spin the wheel to ensure nothing interferes with it.
16. Assemble everything in reverse order.

Now, I need to order a replacement shell from Aliexpress (roughly $20) to get a perfectly working, "brand-new" mouse. Just saved myself a hundred dollars.