British Rail Class 127
BR (Derby) Class 127 4-car Suburban dmu Nos.M51592 (Class 127), M59597 (186), M59640 (186), M51644 (Class 127) in Rail Blue with all-yellow front ends gently rumbling away at St Pancras before departing for Bedford (Midland Rd), 07/75.
In service	1959–1993
Manufacturer	BR Derby
Built at	Derby
Family name	First generation
Replaced	Steam locomotives and carriages
Constructed	1958–1959
Number built	30 sets (120 vehicles)
Number preserved	3 sets (8 vehicles)
Number scrapped	27 sets (112 vehicles)
Successor	Class 317
Formation	4-cars sets: DMBS + TSL + TS + DMBS
Fleet numbers	51591–51650 (DMBS) 59589–59618 (TSL) 59619–59648 (TS)
Capacity	DMBS: 78 TSL: 90 (2 lavatories) TS: 106
Operators	British Rail
Specifications
Car length	64 ft 0 in (19.51 m)
Width	9 ft 3 in (2.82 m)
Height	12 ft 4+1⁄2 in (3.772 m)
Maximum speed	70 mph (113 km/h)
Weight	DMS: 40 long tons (41 t; 45 short tons) TSL: 30 long tons (30 t; 34 short tons) TS: 29 long tons (29 t; 32 short tons)
Prime mover(s)	Rolls-Royce C8NFLH, 2 per power car
Power output	476 hp (355 kW) per power car
Transmission	Hydraulic
Multiple working	■ Originally Blue Square but later changed to ▲Red Triangle
Track gauge	4 ft 8+1⁄2 in (1,435 mm)

The British Rail Class 127 diesel multiple units were built by BR Derby in 1959. Thirty 4-car units were built, formed of two outer driving motor vehicles, sandwiching two intermediate trailers which were classified class 186.^{[citation needed]} The technical description of such as 4-car unit was DMBS + TSL + TS + DMBS.

Numbering

Usage

The units were almost exclusively used on London St. Pancras to Bedford commuter services, which earned the class the nickname "Bed-Pan" units. The class was maintained at a new purpose-built depot at Cricklewood.

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.^{[citation needed]} Power was provided by C8NFLH engines supplied by Rolls-Royce. For further information on the powertrain see British Rail British United Traction.

Replacement

The class 127 units operated one of the most intensive passenger services worked by diesel multiple units and, by the late 1970s, it was clear they needed replacing. It was therefore decided to electrify the Bedford line and replace the Class 127 units with new Class 317 electric multiple units. The class 127 units should have been withdrawn by 1982, however, delays with the new trains meant they had to struggle on in service until July 1983. This was largely due to an industrial dispute with the unions over Driver only operation, which resulted in the new electric trains being stored at Cricklewood depot for nearly a year, awaiting the resolution of the dispute.^[1]

From early 1983, they had commenced operations on the Gospel Oak to Barking line at first running in three-car then finally two-car formations from November 1983 with just the two power cars. The units lasted in service on this line until eventually being withdrawn in March 1984. The units were then stored at Carlisle depot pending reuse, preservation or scrapping. Subsequently, many trailer vehicles saw further use in combination with Class 116 units, based at Tyseley depot in Birmingham. These lasted until October 1993.

Rebuilding

In 1985, 22 redundant power cars, including the first built, no. 51591, were rebuilt to form 11 two-car parcels units. Vehicles were renumbered 55966-987, and formed into sets CH910 to CH920. Units were fitted with roller shutter doors, and were based at Chester depot. The units lasted in service until 1989, when they were withdrawn.

Accidents and incidents

• On 10 October 1964, on an eight-car London St Pancras to Bedford service, a cardan shaft failed on rear car 51591 near Wilshamstead. The failed shaft pierced two fuel tanks, which then caught fire. One person was killed and four injured by jumping from the train. The fire caused only minor damage and was brought under control by the train crew and a railwayman passenger.^[2]

Preservation

Three units have been preserved on heritage railways, although only one of these contains a trailer vehicle.