This has come up before (can't find the thread). The boss is meant to be longer than the body of the brake. If you sand it too much, you'll be clamping the brake between the bolt head and the raise section behind the boss, so it won't be able to turn. How valuable is the frame?
Morning!
I've mounted some new cantilevers in my bike, but found that there is some play :S
the pivot (correct name?) is a bit longer than the cantilever "body"
What should i do here? sand the pivot?