British Rail Classes 112 and 113

4 ft 8+1⁄2 in (1,435 mm)

The Class 112 and Class 113 DMUs used the standard Cravens body used on Class 105s but had a single Rolls-Royce C8NFLH engine rated at 238 hp (177 kW) per car, all of which formed into 'power twins' – two car sets with both vehicles powered.

There were two batches built, the first 50 vehicles (25 sets) had standard mechanical transmission via a gearbox and were allocated the Class 112. The second batch of 50 cars (25 sets) had hydraulic transmissions, and became Class 113s.

The cars were built for services in the LMR Central Division and in the Liverpool - St Helens area, where the gradients in the Lancashire & Yorkshire area required more power. Both types also spent some time working from Cricklewood.

The gross weight of a set with all seats occupied was approximately 70 tons, giving 6.8 hp (5.1 kW) per ton. Empty, it was 8.1 hp/ton, which compared favourably with 5.7 hp/ton that the Cravens power/trailer had.

Lot No.	Diagram	Car Type	Qty	Fleet numbers	Notes
30533	602	Driving Motor Brake Third (DMBS)	25	51681–51705	Class 112
30534	603	Driving Motor Composite with lavatory (DMCL)	25	51706–51730	Class 112
30535	604	Driving Motor Brake Third (DMBS)	25	51731–51755	Class 113
30536	605	Driving Motor Composite with lavatory (DMCL)	25	51756–51780	Class 113

• Coupling Code: Blue Square
• Transmission: Standard Mechanical (Class 112), Hydraulic (Class 113)

Due to incidents that occurred when Class 113 units (which had hydraulic transmission and automatic gear change) were coupled to a unit with mechanical transmission and gear change - usually, a Class 112 - the Class 113 units were changed to the Red Triangle coupling code (the Red Triangle code had previously been used for the early Derby Lightweight DMUs used in the Leeds area, but those were all now withdrawn). The basic problem occurred when a unit being driven automatically (Class 113) failed to mesh with a unit that could not be driven automatically (most Blue Square types). The latter units tended to catch fire. If such a pairing occurred, the driver of the automatically driven unit was supposed to drive it as if it were a mechanical transmission unit, so the two units gears would work together.

If an automatic transmission unit was driven from a mechanical transmission unit the problem did not occur, as the automatic drive unit would change gears as if it was a mechanical drive unit. The Class 112 and 113 units looked similar and one assumes this led to the driving errors. By changing Class 113 to Red Triangle, the incompatible coupling should not occur.

The first withdrawal was M51780 in February 1962. Four more cars were withdrawn in 1964 (M51770), 1966 (M51763) and 1967 (M51705, M51724). General withdrawal of class 112 began in November 1968 – 29 cars were withdrawn that month, and was completed in November the following year. General withdrawal of class 113 began in February 1969, and was completed in July the same year.^[1] Some were cut up at BR workshops such as Derby and Doncaster, but most were sold to scrap merchants. The last of these were broken up in 1971^[2], although two units survivied in industrial use until 1982^[3]. None were preserved.^[4]

By 1973 ^[5], two units, M51692 and M51691, where in use by British Steel at Shotton Works on Deeside. Here they were renumbered PERMINANT WAY 1 (51691) and PERMINANT WAY 2 (51692). They were used as a mobile work vans by the perminant way staff and were not self-propellled, having there engines removed. The were last noted on site derelict in September 1982 ^[3].

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