New South Wales 73 class locomotive

4 ft 8+1⁄2 in (1,435 mm) standard gaugeWheel diameter40 in (1,016 mm)Wheelbase26 ft 6 in (8.08 m)LengthOver headstocks:
36 ft 0 in (10.97 m),
Over buffers:
39 ft 4 in (11.99 m)Width9 ft 3 in (2.82 m)Height13 ft 6 in (4.11 m)Axle load12 long tons 5 cwt (27,400 lb or 12.4 t)Loco weight49 long tons 0 cwt (109,800 lb or 49.8 t)Fuel typeDieselFuel capacity500 imp gal
(2,300 L; 600 US gal)Lubricant cap.Engine:
42 imp gal (190 L; 50 US gal),
Transmission:
58 imp gal (260 L; 70 US gal),
Final drive:
3.25 imp gal
(14.8 L; 3.90 US gal)Coolant cap.80 imp gal (360 L; 96 US gal)Sandbox cap.10 cu ft (0.28 m³)Prime moverCaterpillar D379 series BRPM range550-1400Engine typeFour-stroke V8 dieselAspirationTurbochargedCylinders8Cylinder size6.25 in × 8 in
(159 mm × 203 mm)TransmissionVoith L4r4U2, with Gmeinder Type GM170/EHA/469 and GM170/E/327B final drives

Performance figures
Maximum speed	40 mph (64 km/h)
Power output	Gross: 700 hp (522 kW), For traction: 650 hp (485 kW)
Tractive effort	Continuous: 25,000 lbf (111.21 kN) at 5.4 mph (8.69 km/h)

Career
Operators	NSW Department of Railways
Number in class	50
Numbers	7301-7350
First run	5 October 1970
Preserved	7307, 7320, 7321, 7324, 7329, 7335, 7344, 7350
Current owner	Invicta Sucrogen Mackay Sugar Plane Creek Sucrogen Proserpine Mill
Disposition	15 in service, 8 preserved, 16 stored, 11 scrapped

The 73 class is a diesel-hydraulic locomotive built by Walkers Limited, Maryborough for the New South Wales Department of Railways between 1970 and 1973.

The New South Wales Department of Railways placed an order in October 1969 with Walkers Limited, Maryborough for 20 B-B shunting locomotives.^[1] These were the only New South Wales locomotives to be built in Queensland.^[2]

The first unit was delivered in October 1970. When the whole of the first order had arrived, all steam shunting on the North Coast line and the Sydney Metropolitan area, as well as at Goulburn had been replaced. In July 1971 a further 30 units were ordered. The last of these arrived in March 1973 and this brought to an end all remaining steam shunting operations in New South Wales.^[1]

The New South Wales Department of Railways purchased the class mainly for shunting and their prohibition from mainline use was 'officially' due to the lack of vigilance controls. However, despite its absence, the class was still seen on many suburban trip workings and when mainline operation was a necessity, there seemed to be no hesitation to use them.

One advantage a diesel-hydraulic locomotive has over a diesel-electric variety is its ability to negotiate up to 300mm of water over the tracks. Big floods in March 1976 gave 7323 an opportunity to show off its swimming ability when water covered the line near Bourke and this locomotive was used on a couple of freight trains and a ballast train from Nyngan to Bourke and return. At least two other occasions when their water resistance was put to use was Menindee in 1976 and Hexham in 1977.

Multiple unit operation was common, although the flood event at Hexham is the only known occurrence of triple-heading. A number of units were fitted with exhaust gas scrubbers for use on Eastern Suburbs Railway construction in the 1970s.^[3]

As an example of the spread of the members of the class throughout the system, the fleet was allocated as follows as at 30 August 1977:

Depot	Allocation
Eveleigh	7301–7314, 7317, 7321, 7339–7345
Goulburn	7315, 7316
Cootamundra	7319
Junee	7320 (actually working at Albury)
Lithgow	7326
Orange	7322
Dubbo	7323, 7324
Parkes	7325
Broadmeadow	7327–7338
South Grafton	7318
Werris Creek	7346 (actually working at West Tamworth), 7347
Yeerongpilly	7348–7350

With a reduction in locomotive hauled passenger trains and the closure of a number of yards, withdrawals began in February 1987.^[4] By October 1991 only three remained in service with SRA FreightRail.^[5] One was repainted into CountryLink livery for use as a depot shunter at the XPT Service Centre.^{[citation needed]}

Disposals commenced in 1990 with three sold to the Canberra Railway Museum.^[6] Four were sold to the Manildra Group in 1991.^[7] Many were sold to Queensland sugar cane companies for conversion to 610 mm (2 ft) gauge.^[8] A number have also been preserved.^[9][10][11]

7301 & 7344 were placed on RailCorp's Heritage & Conservation Register.^{[when?][12][13]} 7301 was subsequently scrapped in January 2014.^[14][15]