On April 22, 1995, at 1051 hours Pacific daylight time, a Waco UPF-7, N20971, sustained substantial damage when it nosed over while landing at Chino, California. The privately owned and operated aircraft was on a personal solo flight. Visual meteorological conditions prevailed and no flight plan had been filed for the operation. The certificated private pilot was not injured. The flight had originated from the Chino airport at 1030 on the day of the accident. The pilot stated that she planned to perform some touch-and-go landings at the home base airport. She said that the automated terminal information service (ATIS) "information Lima" was reporting runway 08 as the active runway with the winds from 090 degrees at 10 knots gusting to 20 knots. According to Chino Air Traffic Control Tower (ATCT) information, the pilot was cleared for takeoff at 1046 hours. During the takeoff roll, the wind direction reversed to 290 degrees at 6 knots. At 1105, a terminal observation reported the wind as 270 degrees at 10 knots. According to the pilot, she received amended pattern instructions during her takeoff roll. She was requested to make a south departure and to reenter the pattern on a downwind for runway 26. During the landing roll, she stated that she experienced directional control problems due to wind conditions. During her attempt to control the aircraft, she said she believed she had inadvertently applied the brakes which had caused the aircraft to nose over. A postaccident inspection of the aircraft conducted by the owner's mechanic revealed that the attachment link of the return spring for the left master cylinder had separated. According to the maintenance manual for the Hayes No. D-87-36 brake master cylinder, the assembly is designed so that some brake fluid is added to the pressure side of the piston during the return stroke. However, if the relief port is not opened by a complete return of the piston when the brake is released, pressure can build up in the system, causing the brake to drag or lock.