Furness was released by Pittsburgh after playing all 16 games in the 1980 season and he ended his playing career in 1981 with the Detroit Lions. After retiring from the NFL he became the defensive line coach for Michigan State from 1982–1990, where he worked under his former Steelers defensive coordinator George Perles and helped lead the team to two Big 10 Conference titles, a victory in the 1988 Rose Bowl and appearances in five additional bowl games. During this period he earned a Masters Degree in Athletic Administration from Michigan State University and was inducted to the University of Rhode Island Athletic Hall of Fame in 1987. He rejoined the NFL in 1991 as an assistant coach for the Indianapolis Colts before returning to the Steelers for his final two years as a defensive line coach (1992–1993). In 1999, he was named as one of the "50 Greatest Rhode Island Sports Figures" of the 20th Century by Sports Illustrated magazine, earning the 14th spot on the list.
Furness died unexpectedly of a heart attack on February 9, 2000. He is survived by two sons, Zaban and Zack Furness, a professor at Penn State University.