On August 15, 2000, approximately 1230 Pacific daylight time, a Boeing E75 "Stearman," N450UR, registered to and operated by Evergreen Vintage Aircraft, Inc., and being flown by a commercial pilot, sustained substantial damage during a loss of control on landing roll at the McMinnville Municipal airport, McMinnville, Oregon. The pilot was uninjured. Visual meteorological conditions existed and no flight plan had been filed. The flight, which was personal, was operated under 14CFR91, and originated from Salem, Oregon, approximately 1200. The pilot reported that upon returning to McMinnville he made a practice stop and go landing and that, "During my second approach the winds remained light and variable and after the second 3 point landing during the rollout phase it felt like a gust of wind hit the airplane causing it to veer to the right. My application of full left rudder and brake failed to maintain directional control." (Refer to attached NTSB Form 6120.1/2) A witness reported that he "saw full left rudder and heard the squeal of the tire, but the airplane continued around to the right and rocked over hitting the left wing tip on the runway." (Refer to attached statement) The 1253 local surface winds reported for the McMinnville airport were from 010 degrees magnetic at 3 knots. The 1153 local surface winds reported were variable at 3 knots. The 1353 local surface winds reported were variable at 4 knots. Post-crash examination of the aircraft revealed a crack in the lower left wing aft spar outboard, which required either replacement of the spar or a splice at the crack. The aircraft was subsequently ferried from McMinnville to Portland, Oregon, by an ATP rated pilot. He reported that after arrival, and while taxiing at Portland International airport, he applied full right rudder and the steerable tailwheel locked the aircraft into a right turn. (Refer to attached statement) Further examination of the aircraft by an inspector from the Federal Aviation Administration's Hillsboro Flight Standards District Office revealed that the left control cable spring was not attached at the bellcrank behind the rear pilot seat. With the right control cable spring still attached and the left spring disconnected, the tailwheel would then favor a right turn condition regardless of the position of the rudder. (Refer to attached statement)