On August 23, 2022, about 0930 Pacific daylight time, a Champion 7GCBA airplane, N9512S, was substantially damaged when it was involved in an accident near Athol, Idaho. The pilot and passenger were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot reported that the first flight of the day in the tailwheel airplane was uneventful. The second (accident) flight was also uneventful from takeoff to touchdown; during the landing roll, the right brake was inoperative, which resulted in the airplane veering to the left and off the runway surface into a ditch. The right main landing gear then collapsed, which caused the right wing to impact terrain. Postaccident examination of the airplane by a Federal Aviation Administration inspector revealed that right brake master cylinder piston rod had disconnected from the right rudder pedal assembly, and that the cotter pin was missing from the clevis pin that connected it. The clevis pin was located under the right-side floorboard. Minor wear and markings on the clevis pin cad plating were consistent with the pin being installed; no wear or markings were noted in the cotter pin hole. The cotter pin was not located. The left pedal was properly connected with a cotter pin. The airplane had undergone a conversion to a hydraulic toe brake rudder assembly in October 2019. According to the pilot, the airplane had flown about 12 hours since the conversion. The airplane’s annual inspection was accomplished 12 days and about 1.3 hours (tachometer time) before the accident. The mechanic who performed the inspection stated that he inspected the right brake system and did not recall or notice if a cotter pin was installed in the clevis pin. The mechanic further stated that, if he had noticed a missing or bad cotter pin, he would have replaced it.