The more I use my 5er air brakes during a long windy, downhill run, the more touchy my air brakes become. In other words, when I use my air brakes often they engage with a little more force. Before ...
The more that the brakes are used the hotter they get along with the drums. This will reduce the gap between the shoes and the drum which can cause the brakes to sometimes engage harder. Until they get hot enough to fade, then they don't work well or not at all. Better to follow the good advice here about using gearing and save those brakes.