British Rail Class 35

The British Rail Class 35 is a class of mixed traffic B-B diesel locomotive with hydraulic transmission. On account of their Mekydro-design hydraulic transmission units, the design became known as the Hymeks.

British Rail Class 35
Preserved D7017 at Minehead in 1979
Type and origin Power type Diesel-hydraulic Builder Beyer Peacock (Hymek) Ltd Serial number 7894–7938, 7949–8004 Build date 1961–1964
Specifications Configuration: ​  • Whyte B-B  • UIC B'B' Gauge 4 ft 8 1⁄2 in (1,435 mm) standard gauge Wheel diameter 3 ft 9 in (1.143 m) Wheelbase 36 ft 0 in (10.97 m) Length 51 ft 8+1⁄2 in (15.761 m) Width 8 ft 10 in (2.69 m) Height 12 ft 10 in (3.91 m) Loco weight 75 long tons (76.2 t) Fuel capacity 800 imp gal (3,600 L; 960 US gal) Prime mover Bristol-Siddley / Maybach MD870 Transmission Hydraulic. Stone-Maybach Mekydro type 6184U MU working Yellow Triangle Train heating Steam generator Train brakes Vacuum
Performance figures Top speed 90 mph (145 km/h) Power output Engine: 1,700 bhp (1,270 kW) Tractive effort Maximum: 46,600 lbf (207.3 kN) Brakeforce 57 long tons-force (568 kN)
Career Railroad(s) British Railways Number D7000–D7100 Nicknames Hymek Axle load class Route availability 6 Retired 1971–1975

The type was developed for the Western Region of British Railways, which had opted for lightweight locomotives with hydraulic transmission when allocated funds under the British Railways Modernisation Plan of 1955. One hundred and one of the class were built between 1961 and 1964 when it became apparent that there was a requirement for a medium power diesel-hydraulic design for both secondary passenger work and freight duties.

They were allocated to Bristol Bath Road, Cardiff Canton and Old Oak Common. None of the class was named. Withdrawal from service began in 1971, and by 1975 all had been withdrawn. Their early withdrawal was caused, primarily, by BR classifying the hydraulic transmission as non-standard. Four examples survived into preservation.