The "Brakes Applied" trigger really only works if you are operating with a very high level of deceleration (momentum). I see you have Deceleration Level assigned to a variable channel, which is fine, but you need to turn that knob up until your tank coasts for a good length of time. "Braking" occurs when, while coasting, you move the throttle stick in reverse, but not so much as to stop the tank completely, rather only enough to increase the rate of deceleration (ie, cause it to slow down faster than it would if lelft to coast).
Since our models don't actually coast unless we artificially create this effect, and even then it doesn't last long, the fake braking effect, which is trying to undo our already fake coasting effect, is of even a shorter duration, and it can be tricky to get it to occur. The best chance is to set momentum to the max level, and then get your tank going as fast as possible, before trying to brake gently.