Incident Overview
The pilot, flying from the front seat, was aware of a tailwheel shimmy condition prior to the flight. Upon touchdown, the aircraft's tailwheel began to oscillate. Marks on the runway showed tailwheel tire scuffing from the touchdown area and beyond. A second solid scuff mark associated with the left wheel was observed as both scuff marks diverged left of the runway centerline.
Post-Crash Examination
Post-crash examination revealed that the rear right brake-pedal had disconnected from the connecting rod to the forward right brake-pedal. This disconnection rendered the forward right brake-pedal unusable. The disconnection occurred at the rear right brake-pedal attach eye, and one separation surface was observed to be clean whereas the opposing side was dirty. Cracks were observed inside the attach eye radii, as well as the opposing end of the pedal.
The right-main landing gear separated during the event.
Tailwheel Assembly Findings
Examination of the tailwheel assembly revealed that the hexagonal nut which holds the inner lock ring in place had become loose, allowing the lock ring to shift. This allowed the two lock ring pins to shear, thus allowing the tailwheel to oscillate or 'shimmy' during roll.
Probable Cause
The disconnection of the rear right brake-pedal at the attach eye due to cracks, and tailwheel shimmy due to a loose hexagonal nut allowing lock ring pins to shear.