The SD42/6 was introduced by Crossley in 1948, being a 7ft 6in wide single-deck chassis with a wheelbase of 17ft 7in. It was powered by a Crossley 6-cylinder 8.6 litre direct injection oil engine, and was fitted with triple servo brakes. Transmission was by a single dry plate clutch and 4-speed constant mesh gearbox.
In 1949, theSD42/6 was superseded by the SD42/7 model. This was basically the same chassis as its predecessor, the main difference being in its gearbox.
The SD42/7 was offered with a choice of 4 or 5-speed constant mesh gearbox, or a 4 or 5-speed synchromesh box, all still retaining the single dry plate clutch. Crossley bodywork was available on these chassis, although a vast number carry coachwork by other manufacturers. Production of the SD42/7 ended in 1951.