It is not silver soldered on. Instead, a hole was drilled into the brake down between the threads, and a steel pin was then inserted into the hole. The pin was welded over, and then the brake was turned to clean up to weld, then refinished. You can usually find the location of the pin and, using a Dremel with a cut-off wheel, grind away on the brake until you can get the pin out. At that point, you unscrew the brake.
-Troy