Here are some photos of my rear brake upgrade on my m-bike:
I could not use existing disc brake on rear with with disc brake in place, so replace it with a caliper brake. Braking performance was not adequate, so I decided to upgrade to cantilever brake type. I saw an adapter online, but it was $77, so decided to make the adapter. I had some scrap cutoff aluminum, 3/4" thick, so I sued it. I simply drew the design on the metal freehand and used my bandsaw to cut the piece, then drilled and tapped the holes for the bosses. Temporarily I am using zip ties to hold bottom fingers onto frame, but will make something more solid soon.
Braking power is extraordinarily good. I can lock up the wheel if I want to. Thousand times better than caliper brakes, and as good performance as disc brake.
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