Steve McQueen was diagnosed with cancer the month after filming had ended. He first began to suspect his condition in the autumn of 1979, while he was shooting scenes for this film on location in Chicago.
When Steve McQueen arrived at one of locations used for the film, he was checked into a really nice hotel with all the amenities available at the time. After he found out that the crew was staying in a cheaper motel nearby, he checked out of the hotel and stayed in the motel with the crew.
Steve McQueen came up with the idea of going against his famous car racing abilities by portraying Papa Thorson as a terrible driver.
According to numerous biographies and documentaries on Steve McQueen's life, one of the first signs of problems relating to the cancer in his lungs (which would claim his life) occurred when shooting a scene in which McQueen is running down the street and turns a corner. When the director yelled, "Cut!", McQueen didn't come back around the corner. McQueen was found leaning against a wall trying desperately to catch his breath.
Ralph Thorson: The Real "Papa" Thorson plays the bartender at the bar where Steve McQueen drinks after a character commits suicide.