I would try adjusting them first.  There is clevis rod that sticks through the axle, has a nut on it,  tighten it a few turns, just enough they don't drag.
   It has  ball bearings for rollers inside the brake housing. When you push the pedal your are pulling the balls up a ramp to tighten.   Sometimes when there is to much slack they hammer when going out. The other thing that can do it  rust or something on the pads that grab. Easiet way to tell is when going SLOW push the brake pedal down as easy as you.See if you can get it to not grab.
  They are mechanical brakes.   Dry brakes.   oil on them is no good.Make sure the drain holes are open on the bottom of the housing.