My guess is the brake shops are accustomed to working on disc brakes or Bendix. From what I've read from the Model A guys, there is lots that can go wrong besides adjustment: groves worn in the backing plates, worn actuator bushings and frozen rusty parts, loose anchor pins, etc.,etc. My own experience confirms this. On Bendix drum brakes they wear grooves the backing plates. Hucks seem to be less prone to such wear issues but rust can be an issue. I wonder if Huck made the mechanical brakes on 30s trucks. I have an old book. I'll go look.
