On April 28, 2002, approximately 1200 mountain daylight time, a Cessna A185E, N4730Q, piloted by an airline transport pilot, sustained substantial damage when the airplane ground-looped during landing at the Greeley/Weld County Airport (GXY), Greeley, Colorado. Visual meteorological conditions prevailed at the time of the accident. The instructional flight was being conducted under the provisions of Title 14 CFR Part 91 and was not operating on a flight plan. The instructor pilot and airline transport pilot-rated dual student reported no injuries. The local flight originated approximately 1100. The pilot receiving instruction said, "Late in landing roll on runway 9 (6,210 feet by 100 feet, dry asphalt) at approximately 25-30 mph brakes were applied and left brake failed due to ruptured brake line. Airplane veered right and ground-looped causing left wing tip and left elevator to contact runway." An examination of the airplane revealed the outer portion of the front main spar, two ribs, and a portion of the rear spar to the airplane's left wing were bent upward and aft. The airplane's left wing tip was broken aft. The top skin of the left wing showed wrinkling. The left aileron was bent slightly upward. The bottom left elevator skin showed scraping. Flight control continuity was confirmed. An examination of the airplane's engine and engine controls showed no anomalies. An examination of the left main landing gear showed that a portion of the left wheel rim was broken. The left tire showed heavy rubs in the outer wall and tread. The left brake line was cracked, flattened, and leaking brake fluid.