hi i have i problem, how does not )

well i have to DC motor they run on 36v and they have a 40amp trip
breaker , ho yes i forgot its a big scrubber. well the problem is
this if a let run but motor for i while the breaker will trip and if a
disconect one motor the breaker will not trip. i check both motor i
think i swap back and forth and both motor works as long one only run.
is any way to see if the breaker is bad or one of the 2 motor.