During preseason testing, the team was unable to isolate the cause of repeated gearbox failures, and at the season opener at Phoenix, both cars suffered failures. At the next race in Brazil, it was decided to run five forward speeds instead of six. Despite the reduction in gearshifts throughout the race, Mansell's car failed when his gearbox stuck in first gear, and Patrese managed to limp home in second place just as his gearbox was giving up. When mechanics stripped down the gearbox after the race, the unused sixth gear showed signs of wear, indicating that other gears had come into contact with it. The problem was traced to the clearance between the gears changing as the gearbox built up to its 140�C (284�F) operating temperature. The preloading through the shafts that held the gears was changed for Imola, and from then on the gearbox worked almost flawlessly.