According to the pilot in the tailwheel-equipped airplane, during a wheel-landing the airplane yawed left and he applied right rudder to counter the yaw. The tail descended to the runway and the left yaw increased. He countered the left yaw with a right brake application as well as the right rudder application. He recalled that the right brake application was "completely ineffective" and the airplane exited the left side of the runway. The airplane entered the rough gravel surface on the left side of the runway, and the pilot applied left rudder and left brake to intentionally ground-loop the airplane. The right wing struck the ground, and the airplane came to a stop. The airplane sustained substantial damage to the right wing and aileron. Post-accident examination of the airplane's brake system by Federal Aviation Administration Aviation Safety Inspectors revealed that the cotter pin and clevis that connects the right brake cylinder connecting rod to the inner right brake pedal connection point was detached and unrecovered. The pilot reported that there were no mechanical malfunctions or failures with the airplane prior to landing that would have precluded normal operation.