British United Traction

British United Traction

Infobox EMU
name = British Rail British United Traction

imagesize = 300px
caption =
background = #012545
Manufacturer =
Family =
Formation = unknown
Built = unknown
InService = 1953 -
Weight =
Capacity =
MaxSpeed =
Gauge =
Brakes =
Engine = 9.6 litre, 125 bhp (93 kW) AEC.--------- 9.8 litre, 125 bhp (93 kW) Leyland. 11.3 litre, 150 bhp (110 kW) AEC. ------- 11.1 litre, 150 bhp (110 kW) Leyland. 15 litre, 230 bhp (170 kW) Leyland/Albion
Operator = British Rail

British United Traction (BUT) was a joint company owned by the Associated Equipment Company and Leyland Motors Ltd which produced railway equipment and trolleybuses.

Early British Railways DMUs

BUT produced 11 lightweight diesel multiple unit vehicles for British Railways during the 1950s, numbered 79740-79750. They were of three different types (DMS, DMBS and TS), and could be made up into two- or three-car units. They were not very successful and were withdrawn at an early stage, so never received TOPS classification.

First Generation DMUs

BUT also built the powertrain for the majority of British Railways' First Generation diesel multiple units.


The engines mainly had six horizontal cylinders and were made in several sizes:

* 9.6 litre, convert|125|bhp|abbr=on AEC.--------- 9.8 litre, convert|125|bhp|abbr=on Leyland.
* 11.3 litre, convert|150|bhp|abbr=on AEC. ------- 11.1 litre, convert|150|bhp|abbr=on Leyland.
* 15 litre, convert|230|bhp|abbr=on Leyland/Albion.

AEC and Leyland engines were those designed and built by the respective companies and were not badge engineered except for BUT badges.Six and eight cylinder Rolls Royce diesel engines were also used.The first post war light weight DMUs 1954 -- 1969 are reputed to have had pre war Leyland 8.6 litre horizontal diesel engines fitted. It would be nice to have this confirmed.

Turbo-charged versions of the 11.3 litre and 15 litre engines were available, boosting the power outputs to convert|200|bhp|abbr=on and convert|275|bhp|abbr=on respectively. The turbo-charged versions were not used by British Railways but they were used by Ulster Transport Authority.

Some engines were badged AEC, some Leyland and some Leyland-Albion.

Engines were genuine AEC or Leyland, each type carrying B.U.T. badges.

Transmission systems

Most units had Standard Mechanical Transmission. This comprised a fluid coupling, a freewheel and a four-speed epicyclic gearbox. The freewheel facilitated gear-changing and also had an important safety function. If an engine seized, the freewheel would disengage and give protection against transmission damage and possible derailment.

A small number of units had hydraulic transmission, using a torque converter.

Coupling codes

The level of standardisation achieved with BR's first generation DMUs was much higher than it is with modern DMUs. All had side buffers, screw couplings and vacuum brakes and the majority had the standard Blue Square coupling code system for control of engine speed and gear-changing. There were some units with non-standard coupling codes but they were a small minority. The coupling codes were:

* Blue Square, standard mechanical transmission
* White Circle, early mechanical transmission
* Yellow Diamond, early mechanical transmission
* Red Triangle, hydraulic transmission, Lysholm Smith (Leyland) torque converter
* Orange Star, hydraulic transmission, Twin-disc (Rolls-Royce) torque converter

Non-BUT engines

Some first generation DMUs were fitted with Rolls-Royce engines. Three types were used:

* Six cylinder, convert|180|bhp|abbr=on
* Six cylinder supercharged, convert|230|bhp|abbr=on
* Eight cylinder, convert|238|bhp|abbr=on

The six cylinder engines usually drove through standard mechanical transmissions but the eight cylinder engines were usually coupled to Twin-disc (Rolls-Royce) torque converters.

Mixed running

Rolls-Royce devised a system which enabled DMUs with mechanical and hydraulic transmissions to work together. The British Rail Class 127 units were fitted with this system and given the standard Blue Square coupling code, instead of the Orange Star code given to the British Rail Class 125 units.

There was a gear-change lever (marked D-3-2-1) on the driver's desk and it worked as follows:

* Hydraulic stock only: the lever was moved to "D" and no gear-changing was necessary
* Mixed mechanical and hydraulic stock: the driver changed gear as normal (with "D" corresponding to fourth gear) and the gear-change signals were ignored by the units with hydraulic transmission

It was a good idea but it created problems in practice. If the mechanical stock was at the back, the driver might forget to change gear and this could lead to gearbox damage. In 1969 (after a serious accident in 1968) the Class 127s were re-labelled with the (then disused) Red Triangle coupling code and mixed running was discontinued.

ee also

* List of British Rail classes

External links

* [ The ACV/BUT four-wheeled railcars]
* [ Technical information on first generation DMUs]

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