Team Penske designed the PC12 chassis for the 1984 season, but due to increased competition from rival chassis builder March and its all-new 84C model, Penske set aside its PC12 and purchased 84Cs for Mears and teammate Al Unser to drive at the 1984 Indianapolis 500. Mears showed speed from the start of the month and qualified third, on the outside of the front row alongside pole winner Tom Sneva and Howdy Holmes. Mears used the outside line of the third starting position to take the lead and kept it for the first 24 laps. Defending race winner Tom Sneva was Mears’ only serious competitor until a broken CV joint ended Sneva's day. Mears led a total of 119 laps and finished two laps ahead of second-place finisher Roberto Guerrero. His race average speed of 163.612 mph broke the 12-year-old record set by Mark Donohue in 1972, when he gave Team Penske its first win at the Indianapolis Motor Speedway.