Thank you for your inputs 
In retrospect it was an easy fix indeed. It was another story from the beginning, when you're brand new, recently unpacked locomotive shortens out and you have no knowledge why. I learned a lot during this process, since I never tackled this type of problem before.
Concerning the question on plastic brakes or not. I'm not sure if plastic is better alternative. Yes! No short circuits. But it's more brittle than brass. Brass can be bent, soldered and manipulated.
In my case, if the brake shoe bracket have been in plastic, I probably had to glue the broken part together again.
