The vehicles were the first type to be built at Derby with the longer 63 1/2ft underframe, and the first Derby vehicles to be built from steel. There were worries that there could be delays with the delivery of the huge quantities of steel required (see this letter) that could compromise the scheduled date of laying down the frames on 30th April, 1956. Yet the first vehicles 50001/56001 were delivered in October 1956 so the delays, if any, were minimal. The letter also shows that the order was originally for 50 identical sets all to lot 30209/10.
The ER were duly notified about the potential delay, bringing a response that demonstrated that even before building began there was concern about the weight of the vehicles and the low power / weight ratio, the ER even asking for them to be built as 57ft vehicles instead. They continued to be built as 63 1/2ft vehicles.
The image shows the bogies and underframes under construction at Derby Works.
Description: Cab Design
Description: Power Train
Diagrams & Works Photos
Details about preserved Class 114s can be found here.