Originally Posted by
Retro Grouch
Since the rim is what is causing the pads to wear, why wouldn't the pads wear squarely relative to the rim?
I believe the intent of the linkage that made the pads travel in a straight path is that, without it, the pads tend to hit lower and lower on the rim as they wear and the arc of their travel gets longer. Eventually, unless you keep the the clearance adjusted, they can "submarine" the rim and hit the spokes.
Their downside was wear at the various pivot points and a tendency to vibrate and squeal due to lack of rigidity.