1957 BMW 503 Cabriolet #157
These were the use for the first time of a combined gearbox and differential unit in a transaxle assembly, and the provision of independent rear suspension. The company already had plenty of experience of both systems in their competition cars, the technology of which filtered through to the road models, another case of racing improving the breed.
The engine was an increased capacity derivation of the single overhead camshaft per bank V12 Colombo designed “short” block unit, with factory type reference 213, of 3286cc capacity, with a bore and stroke of 77mm x 58.8mm. It was fitted with a bank of either three twin choke Weber 40 DCZ/6 or 40 DFI/1 carburettors, or the optional six Weber 40 DCN3 assembly, with a twin coil and rear of engine mounted distributors ignition system, to produce a claimed 280bhp.
The engine drove through a shaft running at engine speed to a five speed transaxle which was independently supported from the chassis frame, and then by drive shafts to the independently suspended rear wheels, with wishbones, coil spring and hydraulic shock absorbers to each wheel. Initially the engine had four mounting points and the transaxle three, with sliding joints on the drive shaft between them. However, this proved difficult to maintain in alignment, and after trials, the final derivation was to adopt twin engine and transaxle mounting points with the drive shaft running within a solid tube connecting the two, making the engine and transaxle a rigid unit.