Its not too hard for me to tell if I am having brake problems when I only have two working for me haha...
Having said that I too do scheduled maintenance on the brake system. When I first hookup and hit the road I can tell exactly what my brake status is at the first stop sign before leaving my house area with me applying manual brakes only using the thumb paddles to stop both truck and trailer.
Every 50 miles is usually a pull out at a rest area of some sort and a good walk around is always the first thing done to feel the trailer wheels for excessive heat and the such... Then I hit the rest room...
Even looking for abnormal brake dust is important.
Roy Ken
