Modern cars and trucks use helical gears and synchromesh products in the gearboxes, that synchronize the rotation of gears which might be about to mesh. This eliminates clashing from the gears and can make equipment shifting less difficult. Spur and helical gears are used in the sliding mesh gearbox https://gearbox41963.theideasblog.com/34282808/not-known-factual-statements-about-gearbox