British Rail Classes 112 and 113
Last train from Nottingham Arkwright Street, 1969
In service	1960–1969
Manufacturer	Cravens
Family name	First generation
Replaced	Steam locomotives and carriages
Constructed	1959–1960
Scrapped	1968–1969
Number built	Class 112: 25 sets (50 cars) Class 113: 25 sets (50 cars)
Number scrapped	All
Formation	Power-twin: DMBS-DMCL
Capacity	DMBS: 52 second DMCL: 12 first, 51 second
Operators	British Rail
Lines served	London Midland Region
Specifications
Car body construction	Steel
Car length	57 ft 6 in (17.53 m)
Width	9 ft 3 in (2.82 m)
Doors	Slam
Maximum speed	70 mph (110 km/h)
Weight	DMBS: 30 long tons 0 cwt (67,200 lb or 30.5 t), DMCL: 30 long tons 0 cwt (67,200 lb or 30.5 t)
Prime mover(s)	One Rolls-Royce C8NFLH
Power output	238 hp (177 kW) per car
Transmission	Class 112: Mechanical 4-speed epicyclic gearbox Class 113: Hydraulic
UIC classification	(1A)(A1)+(1A)(A1)
Braking system(s)	Vacuum
Coupling system	Screw-link
Multiple working	■ Blue Square
Track gauge	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.

In 1982,^[1] two units, M51692 and M51691, were in use by British Steel at Shotton Works on Deeside.

Orders

Other technical details

• 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.

Withdrawal

All Class 112s and 113s were withdrawn and subsequently scrapped between 1968 and 1969.

References

Wikimedia Commons has media related to British Rail Class 112.

Wikimedia Commons has media related to British Rail Class 113.

• The Railcar Association
• Motive Power Recognition: 3 DMUs. Colin J. Marsden
• British Railway Pictorial: First Generation DMUs. Kevin Robertson
• British Rail Fleet Survey 8: Diesel Multiple Units- The First Generation. Brian Haresnape
• A Pictorial Record of British Railways Diesel Multiple Units. Brian Golding