Low-loader with a
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difference By R. D. Cater DEMONSTRATED recently at the New Malden, Surrey, premises of Graham Adams Ltd. was an impressive heavyhaulage outfit which the company has had built to its specific requirements. It comprises an Atkinson 6 X 4 tractive unit powered by a Cummins NH 2503 engine driving through an Allison Torqmatic semiautomatic gearbox, and a Dyson 45/60-ton extendible low-loading semi-trailer.
The outfit is suitable for use at gross train weights of up to 65 tons and when used without the deck extension fitted it has an overall length just under 50 ft.; this enables it to be operated without notifying the police. In this state the trailer is 17 ft. 6 in. long in the bed, but the extension increases this by 8 ft. 6 in., giving an overall bed length of 26 ft.
Provided with knock-out rear axles, and with a removable swan-neck, the trailer bed can be laid completely on the ground to facilitate loading or, of course, can be loaded from either end. Removal of the rear axles did not appear to be a difficult job, and the crew completed it in something under five minutes. I particularly liked the attention to detail that bad been paid by the trailer builders. R. A. Dyson and Co. Ltd. It was evident when the trailer was being dismantled and reassembled that everything fitted perfectly.
Mr. Graham Adams, managing director of the operating company, said that they had experienced great difficulty in placing an order for such a special machine. Many of the makers approached would supply only their standard equipment, but Atkinson had really entered into the spirit of the job.
Among the unusual details of the machine are the sliding fifth-wheel which enables the tractive unit to handle semi-trailers with a short top deck as well as its own special trailer: the 250 b.h.p. Cummins engine which can be uprated to 400 b.h.p. should the need arise in the future; the Allison gearbox which provides ratios of 2.82 to 1 on
the converter and has basic ratios of 4.0, 2.82, 2.0, 1.41, 1.0 and 0.71 to I.
Also built into this gearbox is a hydraulic retarder that will absorb 630 b.h.p. at 3,500 r.p.m. and which is controlled by a pedal to the left of the steering column. The ability to provide full-torque gear-changing throughout the whole range is invaluable when handling loads of 50 to 60 tons.
Single-piece propeller shafts equipped with Hardy Spicer 1800 Universal joints drive the Kirkstall heavy-duty rear bogie. This has twin 13.75 in. hub-reduction axles. The primary reduction in each axle is by a hypoid-bevel unit which drives concentric spur-geared secondary reduction trains through half-shafts. Incorporated in the leading axle is an air-operated, locking third differential, which serves the double purpose of reducing tyre wear and giving better traction on bad surfaces. The overall axle ratio is 8.89 to I.
Springing is by standard semi-elliptic leaf springs, with the axles of the rear bogie located by torque rods. The vehicle is equipped with power steering and full air-pressure braking is used throughout. The tractive unit is equipped with 16.5 in. by 6 in. cam-operated brakes all round whilst the semi-trailer has 16.5 in. by 7 in. units at all wheels, and a wheel-and-screw parking brake on each pair of rear wheels.
High-tensile steel is used throughout in the construction of the trailer in order to keep the unladen weight down. Provision is made for side loading and cable-tensioning roller rachets are fitted at each side, and at the rear of the deck to provide a means of "pulling down" load-securing wire cables, which are thought by the operators to be more satisfactory than chains for this purpose. The overall weight of the trailer complete with the extension is 13 tons 17 cwt. and the overall length in the same condition is 44 ft. 3.5 in. All axles on the tractive unit are equipped with 8.37 in. by 20 in, wheels, but those used on the rear axles have 7 in. offset. whereas the front axle employs wheels with a 6 in. offset. Michelin F.20 ZZ tyres are fitted all round. Semi-trailer tyre equipment is four Goodyear 16.00-20. 24-ply. each having a load rating of 725 tons at 12 m.p.h. and 6.65 tons at 30 m.p.h. This will give ample spare capacity when operating at the 30 tons payload normally envisaged by the operators, as when carrying an evenly distributed 30-ton load the rear bogie weight at the ground is 25 tons.
The outfit has a Dyson heavy-duty universalpattern fifth-wheel having transverse as well as fore and aft oscillation. A 3.5/4.5 in. kingpin is employed and reducing collets have been supplied to permit the coupling to be used with the smaller 2 in. king-pin used on the standard semi-trailers.
The sliding mounting of the fifth wheel permits a range of movement of 3 ft. 8 in. giving a foremost king-pin position of 1 ft. 4 in. in front of' the bogie centre line and a rearmost position immediately above the rear axle. There is provision for seven positions in all.