Johncock's winless drought came to an end when he joined the STP/Patrick Racing team ahead of the 1973 USAC season.
At the 1973 Indianapolis 500, a major accident at the start involving Salt Walther, coupled with two days of rain, postponed the race until late Wednesday afternoon.
When the race was held, Johncock's teammate Swede Savage was severely injured in a fiery crash on lap 58.
After a short and muted victory lane celebration, Johncock went to visit Savage at the hospital.
Johncock won the USAC national championship in 1976, snatching the title from Johnny Rutherford in the final race of the season at Phoenix International Raceway.
In 1976 and 1978 he finished third at Indianapolis, and in 1977 he was leading A. J. Foyt when the car's crankshaft broke with sixteen laps to go.
Johncock's last Indycar win was in the opening round of the 1983 CART PPG Indy Car World Series at the Atlanta Motor Speedway driving a Cosworth powered Patrick Wildcat.
Johncock abruptly retired from IndyCar racing during the first week of practice for the 1985 Indianapolis 500, just before qualifications.
Johncock completed a sixth-place finish in the 1991 Indianapolis 500, despite having flu-like symptoms the morning of the race.
While most discredit the race as being rain-shortened, and for its overall miserable memories, Johncock insisted that his car was undoubtedly the fastest on the track, led easily, and was not simply in front at the time of the red flag by chance.
After stopping for pictures at the Yard of Bricks, Johncock got into the driver's seat of the bus and took his family for an impromptu second, and final, lap around the track.
[4] As Johncock was not given an official Victory Banquet in 1973 owing to the fatality that occurred during the race and because of the excessive delays, the Speedway offered an official Victory Banquet to receive his Champion Driver's Trophy, first awarded in 1988 for race winners and since 2013 has been awarded on milestone anniversaries, Johncock expounded on his life outside of racing, saying that farming was what he was always "caring to do.