British Rail Class 129

The Class 129 was a class of single-car Diesel Multiple Unit built in 1955 for British Rail. Only three were built by Cravens and were introduced in 1958. The class was built for parcels traffic like the Class 128. One unit (55997) survived into departmental service being named 'Hydra'. The driving ends of a Class 129 car bore a visible similarity to that of the British Rail Class 105, also built by Cravens.

Departmental Usage
One unit, M55997, was converted as a test bed for hydrostatic drive in 1980, was renumbered RDB 975385, and named Laboratory 9 ‘Hydra’.

It was fitted hydrostatic transmission having the normal Leyland 680 six cylinder engine driving two Rexroth Hydramatic axial piston pumps. Each pump supplied fluid to a Volvo fixed displacement compact axle-end motor which drove the axle directly. The maximum system pressure was in the order of 400 bar.

This arrangement was only fitted to one bogie, the other one retaining its normal drive but with the cardan shaft disconnected.

The unit was finally scrapped by Vic Berry at Leicester.