When completing a coupling, you pull forward gently against the locked kingpin to test the connection. The trailer does NOT move but you hear a loud 'clunk'. What does this indicate?

A 'clunk' during the tug test without trailer movement can indicate the fifth wheel jaws are resting ON the kingpin rather than locked AROUND it — a 'false coupling.' This can hold briefly but release at speed or on uneven road, dropping the trailer. Always visually confirm from the side: you should not be able to see daylight between the upper and lower fifth wheel plates, and the locking jaw should be fully closed around the kingpin shank, not the head.