 His best season was 1971, when he drove his own car to 13 top ten finishes and a 16th place points result.At the 1971 Volunteer 500 at Bristol Motor Speedway, Hassler was a relief driver for race winner Charlie Glotzbach.It was not an official win for Hassler, and it is one of only three instances when two drivers drove the winning car in a NASCAR premier series race.