British Rail Class 35

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British Rail Class 35
WSR 7017 79-08.JPG
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
Total produced 101
AAR wheel arr. B-B
UIC class B'B'
Gauge 4 ft 8 12 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 12 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; 84.0 short tons)
Fuel capacity 800 imp gal (3,600 l; 960 US gal)
Prime mover Bristol-Siddeley / Maybach MD870
Engine type V16 Diesel [1]
Displacement 86 L (5,200 cu in)
Cylinders 16
Transmission Hydraulic, Stone-Maybach Mekydro type K184U
MU working T. equilatero.jpg Yellow Triangle
Train heating Steam
Train brakes Vacuum
Performance figures
Maximum speed 90 mph (145 km/h)
Power output Engine: 1,700 bhp (1,270 kW) at 1500 rpm
Tractive effort Maximum: 46,600 lbf (207.3 kN)
Continuous: 33,950 lbf (151.0 kN)@ 12.5 mph (20.1 km/h)[2]
Loco brakeforce 57 long tons-force (568 kN)
Operators British Railways
Numbers D7000–D7100
Nicknames Hymek
Axle load class Route availability 6
Retired 1971–1975
Preserved four preserved, remainder scrapped

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

The class 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 was completed by 1975. Their early withdrawal was caused, primarily, by BR classifying the hydraulic transmission as non-standard.[citation needed] Four examples survived into preservation.


The builder, Beyer Peacock (Hymek) Ltd, was a joint venture between Bristol Siddeley Engines (BSE) (licensed to build Maybach engines), Stone-Platt Industries (licensed to build Mekydro transmissions), and the locomotive manufacturer Beyer, Peacock and Company. At the time they were built, the Hymeks were the most powerful diesel-hydraulic locomotives operating with a single engine - the Maybach MD870. Unlike the higher-powered diesel-hydraulic Warship and Western locomotives in the Western Region fleet (with dual Maybach MD655 engines), the Hymeks were not based on an existing West German design.


When first built, the Hymeks were given a more elaborate livery than many of the contemporary British Railways diesel classes. The main body of the locomotive was the standard dark Brunswick green, but with a lime green stripe along the bottom of the bodywork. The roof was medium grey, and the finishing touch was to paint the window surrounds in ivory white. In the early 1960s, yellow warning panels were added to the lower part of the front ends, in accordance with BR's then-new policy. Following the corporate identity campaign and the change of name to British Rail plus introduction of the "double arrow" logo in 1964, some locomotives received all-over BR Rail blue with small yellow warning panels. This was quickly changed by the return of off-white window surrounds. The final variation was BR blue with full yellow ends, the yellow being extended around the cab side windows.

Not all locomotives received the final blue livery. Numbers 7002, 7013, 7020, 7024 and 7054 (at least) were still in green livery when dismantled at Swindon, whilst photographs of numbers 7003, 7005, 7006, 7008, 7021 and 7060 taken late in their lives whilst still green suggest that these may also not have received a repaint in blue. Some of the green locos did receive the same style of full yellow end, extended round the cab side windows that was applied in the final variation of the blue livery. These included nos. 7000, 7009, 7013, 7014, 7020 and 7092 (at least). 7000 and 7009 eventually received the final blue scheme, 7013 and 7020 were withdrawn in green with full yellow ends. The final colour schemes of 7014 and 7092 are not known.

Of those that were repainted blue, numbers 7007, 7010, 7034, 7036, 7046, 7047, 7051, 7052, 7056, 7057 and 7059 (at least) did not receive the full yellow end, only the small yellow warning panel.

Operational service[edit]

D7033 piloting Abergavenny Castle on a South Wales to London service in 1962

The type was initially employed on secondary passenger services based around Bristol, such as Paddington to Hereford and semi-fast services to the west of England and Wales. Once they had proved themselves more than capable of handling these duties, they were also assigned to express Paddington-Cardiff-Swansea services, displacing King-class steam locomotives. These duties were heavier than they were designed for, and the Hymeks were displaced when Western and Brush type 4 locomotives became available to allow accelerated timings.

Hymeks also worked pickup freights throughout the Western Region as a mixed-traffic design and were used heavily on inter-regional passenger services. This latter often caused operational problems as they would often terminate in areas where there were no trained staff to handle the locomotive once the rostered crew had ‘booked-off’. To avoid these instances, the locomotive would invariably be dispatched back to the nearest Western Region tracks without delay. The Hymeks were capable of operating in multiple, but only with each other. The electro-pneumatic control system (coded “Yellow Triangle”) allowed only one trailing locomotive to be controlled (by one driver): some trains were operated by three locomotives (all at the front of the train), but in these cases only two locomotives were connected in multiple, the third having a separate driver.

Hymeks were used all over the Western Region on mixed traffic services from secondary passenger and parcels through express freight to ballast trains. They were common in all parts of the region from Paddington to Bristol/South Wales/Worcester/Hereford. They also worked to Birmingham and the West of England, but were rare west of Plymouth.

Hymeks were notably used in multiple (up to three locomotives) as bankers on the Lickey Incline, propelling mainly freight trains from Bromsgrove to Blackwell. During trials, it was discovered that the Hymeks changed between first and second gear was at about the speed required to bank a train up the incline, and so they tended to "hunt" between the two gears. Repeated gear changes under full power caused excessive wear and damage, plus excessive heat in the transmission fluid quickly resulted in the locomotive stopping. Hence the simplest way to avoid excessive wear, and the stopping of a train on the incline, was to lock first gear out of action, via the master switch located in each locomotive's A-end cab.[3] With all Lickey bankers allocated to Worcester shed, the main group of five locomotives (D7021 - D7025) and any replacements were all turned on the Worcester triangle, so that the A-cab was always aligned up the incline. Once at the bottom of the incline, each train which required banking would be signalled to the banking locomotives by Gloucester Panel Signal Box, so that the banking crew could then determine if it was necessary to lock out first gear on one or more of the locomotives.[4]

Accidents and incidents[edit]


D7022, a British Rail Class 35 locomotive, in a scrapyard at the end of its life

The aim of the Modernisation Plan, and in particular the rapid conversion of the entire BR fleet to diesel and electric traction, had been to stem BR's financial losses thought to arise partially from the labour-intensive nature of steam locomotive use. Although steam was eliminated from mainline use by 1968, many unsuitable designs of diesel locomotive had been rushed into service in the rush to achieve steam-free operation. The National Traction Plan of 1967/8 decreed that designs proving unreliable, expensive to maintain or non-standard should be eliminated as quickly as possible in order to reduce the number of diesel classes from 28 to 15 by the year 1974. The engineering factions of the British Railways Board, the body that oversaw BR's operations from 1962 onwards, felt that all of the Western Region's diesel-hydraulic fleet should be counted as non-standard and should be withdrawn as quickly as possible. The entire class was withdrawn between 1971 and 1975. They were replaced by Class 37 diesel-electric locomotives made redundant in other regions as a result of a general decline in rail-borne freight traffic throughout the 1960s.

Formal withdrawal was not the end for three locomotives: 7076 and 7096 continued to be officially in non-revenue stock for some years; while 7089 also continued, but renumbered as TDB968005 in the Departmental series.


Four locomotives survived to be preserved.

Number D7076 on the East Lancashire Railway
  • D7017 - West Somerset Railway
  • D7018 - West Somerset Railway
    D7017 and D7018 have been fully restored to working order since withdrawal. D7017 is now operational after a spell of four years out of traffic. D7018 is currently undergoing repairs at Williton Shed, West Somerset Railway and is unavailable for traffic. (On 9 May 2009, D7017 successfully hauled a 350ton test train on the WSR, after a four-year overhaul.[6])[needs update]
  • D7029 - Severn Valley Railway
    D7029 is still undergoing a major restoration, and recently moved from Old Oak Common shed, in west London, to the Severn Valley Railway for further restoration, before a planned return to service in BR blue.[needs update]
  • D7076 - East Lancashire Railway
    D7076 survived, along with sister locomotive D7096, at the Railway Technical Centre near Derby, where they were used as dead loads for research purposes. Warship no. D832 Onslaught was additionally present at this site. Both Hymeks were in poor condition, however it proved possible to rebuild one by using the other as a donor locomotive. D7076 was therefore restored using parts from D7096 and carries the number D7096 internally in one driving cab as a nod to the donor locomotive, which was reduced to a shell and subsequently scrapped.
    Having been restored to working order,[when?] and used on service trains, D7076 was taken out of traffic in late 2008 for repairs to a leaking turbo and coolant faults. The engine was subsequently found to need a complete rebuild, so in an unusual move, a Maybach MD-655 engine from D1041 (Western Prince, stopped for overhaul) was fitted into the locomotive to make it a runner. The resulting loco was nicknamed a "WesMek". However, late 2009 / early 2010 D7076 was taken out of traffic due to the Maybach MD-655 engine developing a liner seal problem.[needs update]

During summer 2011, two ex-Hymek MD-870 engines were discovered in a scrapyard in York, in excellent condition, having been used in a hospital emergency generator set. Both engines were purchased by D7076's owning group, and one has been fitted into D7076, which returned to service at the ELR's July 2011 diesel gala. The other engine is to be retained as a spare.

On the 11th November 2013 it was announced by the ELR:DG that work had started on bodywork repairs at Castlecroft Diesel Depot, and that D7076 will emerge in a new livery ready for their East Lancs Railway Summer Diesel Gala in 2014. In July 2014 D7076 returned to service on the East Lancs Railway in BR Blue Livery with full Yellow ends.

Hymeks in fiction[edit]

A Class 35 Hymek was featured in The Railway Series books by Rev. W. Awdry (the original 'Thomas the Tank Engine' stories). D7101 (a fictional number), later named Bear on account of the growling noise made by his engine, was introduced in book No.23 Enterprising Engines as one of the good diesels. He however has not featured in the Thomas the Tank Engine and Friends TV Series.

A Class 35 Hymek was featured in an episode of Gerry Anderson's The Secret Service. The episode Last Train to Bufflers Halt utilises the blue and white Tri-ang Big Big Hymek as a single unit Bullion Railcar rather than as a proper locomotive. Another Big Big Hymek in the rarer yellow colouring is seen stationary in a siding.


  • Reed, Brian (1974). Diesel-Hydraulic Locomotives of the Western Region. Newton Abbot: David and Charles. ISBN 0-7153-6769-2. 
  • Williams, Alan; Percival, David (1977). British Railways Locomotives and Multiple Units including Preserved Locomotives 1977. Shepperton: Ian Allen Ltd. ISBN 0-7110-0751-9. 
  • McManus, Michael. Ultimate Allocations, British Railways Locomotives 1948 - 1968. Wirral. Michael McManus. 
  • Clough, David N. (2011). Hydraulic vs Electric: The battle for the BR diesel fleet. Ian Allan. ISBN 978-0-7110-3550-8. 


  1. ^
  2. ^ [1]
  3. ^ Lewis, JK, "The Western's Hydraulics", ISBN 978-1-901945-54-6
  4. ^
  5. ^ Hoole, Ken (1982). Trains in Trouble: Vol. 3. Redruth: Atlantic Books. p. 47. ISBN 0-906899-05-2. 
  6. ^ (accessed 11-05-2009)

Further reading[edit]

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