Honda Civic power mirror broken gear shim

Note: The cover photo is of the part that's repaired, not of the print!
I didn't photograph the print, as I thought I'd have to iterate at least once more on the design. When I had installed it, and everything worked, I didn't want to remove the part again.

I recently bought a 2007 Honda Civic and just after buying it, I realised that the power (electric) mirror adjustment on the driver side didn't work in the horizontal plane. The mirror would just wiggle in place when I activated it.

I opened up the mirror:

1. (Manually in my case) move the mirror in the horizontal plane until you can grab the edge of the actual mirror.
2. Grab the bottom and gently, but firmly, pull it towards the rear of the car. Slowly increase force, until the bottom clicks loose.
3. Pull down to release the upper attachment points of the mirror, until it clicks loose. Pay attention, the mirror has two heating wires running to it. Don't suddenly pull it away, you might break those wires. I laid the mirror on the beam between the mirror housing and the car.
4. Remove the two metal coloured screws, one is in the centre and is spring loaded. Take care that it doesn't fly off when you unscrew it. The other is slightly lower and to the side nested in a fairly deep hole.
5. Pull off the mirror mount, it'll make a rasping sound as you pull the threads past the spring loaded pins that grip into it.
6. Unscrew the three smaller headed screws that hold the central electric adjustment assembly and open it up.
7. You may have to remove the rubber cover over the gears. I experienced that sometimes it stuck to the cover, sometimes it stuck to the inner part.
8. Now you can see the gears. Take care that you don't lose the small metal ring that tensions the plastic pins inward.

In my case one of the five pins on the gear used for the horizontal plane adjustment, had been bent and broke off approximately half way. This meant that the teeth on the other pins were not tensioned properly against the thread of the rod, and when they rotated they would slip, and the rod would just wiggle a bit.

Print the replacement

Since the part could not be bought online easily, I started to look for a way to print a repair shim. After some iterations, the current one made the mirror adjustment work again.

I printed it in PLA at .1mm layer height. It came out a bit wonky, since I sliced it with PrusaSlicer. PrusaSlicer's algorithm is terrible for small, narrow and tall objects. It doesn't allow the layers enough time to cool before printing the next one. Still, it worked well enough. I think the shim doesn't actually transfer much of the push/pull force from the gear to the rod. It mainly restores the symmetry and tension so the remaining intact pins can transfer the force.

Note: In my case the pin with the lowest tooth height was damaged. The teeth on the five pins grip into the thread of the rod, and hence they form a spiral. Each pin is unique and the teeth are approximately .75mm higher on each subsequent pin. You can adapt the provided FreeCAD file if you need a different pin. Open up the first sketch, and change the top-right most measurement to move the tooth. However, it might not be strictly necessary. As noted, the shim mainly restores tension, and it might work well enough, even if the tooth is in an non-optimal position.

Install the part

After you've printed the part, cut off the remnant of the damaged pin. Use the created opening to snap the printed part between the remaining four pins. Then push down to slide the cylindrical part all the way down into the hollow centre of the gear. Now re-install the small metal ring over the tops of the pins.

Put the gear in its original place inside the power mirror assembly, and follow the steps above in reverse order to reassemble it. After you're done, pull on the mirror again a few times as if trying to start another disassembly. If you can easily pull the mirror off at this point, you haven't done the reverse steps 3 and 2 correctly, and the mirror will fall off while driving. It takes a surprising amount of force to reverse step 2 and snap the mirror back in place. However be careful and ensure you've aligned everything correctly. Only increase force once you're sure that the alignment is correct, and you're not going to break something.