1958 was a watershed in another crucial way for Formula One. Against a small field of Ferraris and Maseratis, Stirling Moss won the Argentine Grand Prix driving a mid-engined Cooper entered by the private team of Rob Walker, and powered by a 2-litre Coventry-Climax Straight-4. This was the first victory for a car with the engine mounted behind the driver in Formula One. It was also the first World Championship GP win for a private entrant (excepting the Indianapolis 500 where all the entries were technically private entrants using bought-in chassis). The next Grand Prix in Monaco was also won by the same Cooper car, this time driven by Maurice Trintignant and facing more substantial opposition. Powered by undersized engines, the Coopers remained outsiders in 1958 but as soon as the new 2.5-litre Coventry-Climax engine was available, the little British cars went on to dominate Formula One. The 1959 season was effectively the start of the mid-engined revolution, and this season saw fierce competition between the works Cooper of Australian Jack Brabham and Moss in the Walker team's Cooper. The Getrag-modified Citroën Traction Avant transaxle proved to be the Achilles heel of the Coopers, so Walker switched to a transaxle manufactured by ex-Maserati engineer Valerio Colotti. The special transmission turned out to be more unreliable than the standard part, and Brabham took the title with Moss second.