Sachs and sports car driver Dave MacDonald, a 500 rookie, were killed in a fiery crash involving seven cars on the second lap of the 1964 Indianapolis 500. MacDonald was driving a car owned and designed by Mickey Thompson, the #83 "Sears-Allstate Special." Thompson had requested USAC officials to visit his shop in California to inspect the car while it was under construction so that he would not invest money in the car if there was a chance that it would be disqualified at the Speedway. USAC accepted the request and passed the car with its ground effects package. By the time the car reached the Speedway in May, USAC had changed their mind and failed it. Working in the cramped spaces of the garage area, Thompson and crew practically rebuilt the car to meet the new USAC specs. These changes, removal of the fenders, changing to larger tires and increasing the height from two inches to four, made the cars very unstable. Graham Hill tested the vehicle before Indy but refused to drive it in 1963. Masten Gregory crashed earlier in the month due to aerodynamic lift. After MacDonald had qualified and before the race, World Grand Prix Formula One Champion Jim Clark, who knew MacDonald and respected his ability, followed the Californian for several laps. After they pulled in, Clark emphatically urged MacDonald to get out of the car. "Get out," Clark said. "Just get out and walk away." But MacDonald felt obligated to honor his contract with Thompson. Other drivers took Gregory's advice and stayed away from the Thompson cars. Before the race, Gregory approached Formula One driver Jack Brabham, who was alongside MacDonald on the grid, and urged Brabham to allow the rookie a lot of room. Brabham credited Gregory's advice with saving his life.