Powertrain
Unlike other "Heritage" DMU units, the class 127 units had hydraulic transmission (as opposed to the more standard mechanical transmission). The gear selector in the driver's cab had a "D" position where "4" would be on other standard transmission units. As built, these units were coded Blue Square, and were therefore able to work with mechanical transmission units, provided the driver remembered to use 1,2,3,D instead of just selecting D. This was changed to a unique code of Red Triangle when a driver forgot he had a mechanical transmission unit on the rear of his train, which meant this unit was driven only in fourth gear, which burnt out the transmissions on that unit. Power was provided by engines supplied by Rolls-Royce. For further information on the powertrain see British Rail British United Traction.
Read more about this topic: British Rail Class 127