On August 31, 2005, about 1840 Pacific daylight time, a tailwheel equipped Piper PA-22-150, N1829P, sustained substantial damage during the landing rollout at the Mead Flying Service Airport (S70), Mead, Washington. The airplane is registered to the pilot, and was being operated as a visual flight rules (VFR) cross-country flight under the provisions of 14 CFR Part 91, when the accident occurred. The private pilot and passenger were not injured. Visual meteorological conditions prevailed for the flight that originated at Hoskins Field Airport, Olympia, Washington, about 2 hours and 30 minutes prior to the accident. During a telephone conversation with the National Transportation Safety Board IIC, the pilot reported that shortly after touchdown (three-point landing) the airplane developed a significant vibration/shimmy emanating from the area of the tailwheel. He reported that immediately after the onset of the vibration the airplane began to "pull to the right." The pilot applied corrective actions (full left rudder and braking action), however the airplane continued to track to the right and exited the runway edge. After exiting the runway, the airplane collided with a berm and ground looped. During the ground loop, the left wing and tail made ground contact resulting in substantial damage. The pilot reported that a post accident examination of the tailwheel assembly revealed that the left control spring was disconnected. The pilot further stated that he believed the control spring become disconnected as a result of the shimmy during landing.