On January 10, 2003, at 1249 mountain standard time, a Waco SRE, N1252W, lost directional control on landing and struck a runway sign at Prescott Love Field Airport, Prescott, Arizona. The pilot was operating the borrowed airplane under the provisions of 14 CFR Part 91. The airline transport pilot and pilot-rated passenger/owner received minor injuries. The airplane was substantially damaged. Visual meteorological conditions prevailed, and no flight plan had been filed. The flight originated at Prescott about 1215. In a written statement submitted by the pilot, he stated that this was his third flight in the airplane with the owner. The pilot was learning the operational characteristics of the airplane so that he could accompany the owner on future trips. The first flight was flown from the right seat, the other two flights were flown from the left seat. The third flight was uneventful until the landing roll on runway 21L. After a three-point touchdown, the airplane began to veer to the left at about a 10-degree angle. The pilot attempted to correct the turn by applying right brake with the yoke in the full aft position. The airplane continued to turn left, leaving the runway and striking a runway sign, which resulted in the right main landing gear collapsing. Post accident examination of the left main wheel and brake assembly revealed that when the rudder pedals reached full travel, the linkage was beginning to push the brake master cylinder's piston. This resulted in brake application. The amount of brake application was not consistent and it was not noticeably applied every time it was tested. Any pressure applied to the brake in this position did not bleed off with release of the brake pedal. The right brake was not examined since the brake line had been cut during aircraft recovery. The aviation routine weather report (METAR) for Prescott indicated winds at the time of the accident were from 010 degrees at 6 knots.