In 1985, Trueman was diagnosed with cancer. He kept his illness secret for many months. At the 1986 Indianapolis 500 Trueman spent the entire month of May at the track, but was visibly frail and quiet. The race was originally scheduled on his 51st birthday, but rain delayed the race. Bobby Rahal's car was fitted with a "Happy Birthday JRT" decal to celebrate. The following Saturday, May 31, 1986, the race was finally run. With two laps to go Rahal passed Kevin Cogan on a restart, and held on to win. The emotional Rahal nearly broke down in victory lane.