On September 14, 1999, at 1200 mountain daylight time, a Piper PA-22-135 (converted to a PA-20-135, Pacer), N3329A, was substantially damaged during landing rollout at Weld County Airport, Greeley, Colorado. The airline transport pilot and his passenger were not injured. The aircraft was being operated by the owner under Title 14 CFR Part 91. Visual meteorological conditions prevailed for the personal cross-country flight which originated from Larned, Kansas, approximately 2 hours, 25 minutes before the accident. No flight plan had been filed. The pilot reported that when he was 10 miles east of the airport he heard that the wind was 100 degrees at 6 knots, and that the active runway was 35 (runway 27-09 was closed, and runway 03-21 was a dirt runway in unknown condition). He flew over the airport and entered the traffic pattern on a left downwind. The pilot said the landing appeared normal until about 40 to 45 knots when the airplane began drifting to the left of centerline. He said he corrected the airplane back to the centerline, and then it suddenly ground looped to the right. The pilot said that there was a 3 to 4 inch high dirt berm along the side of the runway. He said his left main landing gear and tail wheel impacted the berm, and folded under the airplane. Subsequently, the left wing spar broke at the mid point, and the empennage was twisted 90 degrees. He further stated that the rubber skid marks on the runway indicated that the tail wheel was oscillating, or shimmying (see pilot's statement). The maintenance person, who recovered the airplane, said that the self-centering tail wheel locking device was "well lubricated," which is what the maintenance manual requires. He said aerial application pilots who fly airplanes with similar tail wheel self-centering devices always instruct him not to lubricate their self-centering devices when he performs maintenance on their aircraft. They told him that it was easier to land in a crosswind when their tail wheel self-centering devices were dry.