In 1976, California Golden Seals franchise was moved to Cleveland as the Cleveland Barons. In 1976–77, Klassen played for the struggling Barons and increased his scoring to 14 goals in 80 games. A solid two-way player, he was a consistent contributor to the team; however, it did not help the dismal play of the hapless Barons who won only 47 games in their two NHL seasons. In the 1977–78 season, after playing 13 games for the Barons, he was traded to the Colorado Rockies on January 9, 1978, as part of a deal with Fred Ahern for Chuck Arnason and Rick Jodzio. In Colorado, Klassen played 44 games.