Checking trailer service brakes

It's not that hard.

Chock wheels.

Release brakes.

Get yourself a large trigger clamp and reverse the position of the 'jaws' so that instead of clamping you're pushing apart. Insert between steering wheel and brake pedal, tighten.

Measure the stroke. (tractor and trailer)

Trigger clamp with jaws reversed.

 

Simpler yet...

I use my pin puller. Just wedge it in between steering wheel and service brake pedal after you charged up air system. This is what I do to find a leak along the service line "chain."

Every time I hook a set, I charge system, then release brakes while in gear. Let it settle, then apply brake pedal and listen / watch air gauges for pressure loss and air leaks. It's a good habit to get into. If I have a leak, that's when I'll use pin puller trick to apply brake pedal while I can get out myself and check glad hands and hoses.