Are there any substantial differences between calipers for the front of the bike and those for the rear? Im not talking about the Campy differential ones, but rather about whether one could mount a front caliper on the rear of the bike and vice versa. Thanks in advance for your wisdom.
The difference is in the length of the spindle. The spindle is longer for the front brake, to allow for it to pass through the mounting hole in the crown of the fork. The rear brake mounts on a slender bridge, which is a much thinner platform, so its spindle is shorter. You can certainly mount a front brake on the rear, provided you have sufficient threading on the spindle and/or use a nut instead of the recessed allen nut. In fact, with vintage bikes that were designed for nutted brake mounting instead of recessed, you have to use a front brake on the rear so the spindle is long enough to accommodate the nut.