Trailer or Semi-trailer at Will
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I N conjunction with Taskers of Andover (1932), Ltd.,. John I. Thornycroft and Co., Ltd., has recently supplied two special rigid six-wheeled vehicles with convertible semi-trailers to Bibiani (1927), Ltd., for the transport of mining machinery on the Gold Coast. For this duty a vehicle capable of carrying an indivisible load of 10 tons was required, but, owing to local regulations, it was necessary to obtain special permission to operate with this load. The maximum axle weight permissible is 31tons and it was found possible to keep to this figure by utilizing a slightly modified Thornycroft type KE/DC4/1 chassis in conjunction with a four-wheeled-bogie semi-trailer.
Tractor Chassis Details.
The tractor chassis incorporates the makers' well-known four-cylindered oil engine and is a type specially) suited to overseas conditions and for crosscountry work, due to the wide range of gears available and, in particular, to the patented system of bogie-axle suspension. This allows 11 ins, difference in driving-axle levels and permits either axle to tilt to an angle of 15 degrees.
Owing to the high temperatures in the locality, the drivers' cabs were constructed with a double roof, having an air space between, ventilation being further assisted by a four-piece windscreen and side doors without windows.
Easily Convertible Trailers.
The Tasker concern was asked to design the semi-trailers in such a way that they were easily convertible tp normal four-wheeled trailers, each to carry a load of 6 tons. This was carried out with a minimum of additional parts, the only extras required for the conversion being the drawbar, two brake rods and blank union studs for cutting out of action two of the brake servo cylinders.
The main frame members are of channel steel with the necessary body framing, outriggers and cross-members welded together in a unit. Distance pieces are fitted between the frame and E26
the sub-frame (also constructed as a unit) when used as a semi-trailer, and the projecting part of the sub-frame has a detachable platform for carrying a roll of wire netting. A steel headboard, with rounded corners, and a 'detach= able steel bolster are fitted. The sides and tailboard, approximately 2 ft. 3 ins. amp, are hinged and detachable.
The floor is of oak covered with steel sheeting and is approXimately 16 ft. long and 7 ft. wide.
The axle gear is of normal. Tasker design, with steel spring chairs shrunk on to high-tensile steel axles, 15 ins. by 3 ins, totally enclosed brakes to all wheels, and steel hubs fitted with Timken taper-roller bearings. The wheels, which are interchangeable with those on the towing unit, are fitted with 38-in. by 9-in. Dunlop pneumatic tyres.
As a semi-trailer, each brake is operated by a separate ClaytonDewandre vacuum-servo cylinder interconnected with the cylinder on the tractor.
When effecting the conversion the sub-frame distance-pieces and the rear platform are removed and the 'subframe moved forwards and bolted direct to the main frame. The sub-frame on
the tractor chassis is removed, the turntable trunnion brackets detached and the top turntable ring bolted direct to the appropriate 'main frame crossmembers. The axle and spring assemblies are detached and refitted in the appropriate positions and the drawbar attached to the front of the forecarriage. The front-wh6e1 brakes on the trailer thus formed are not used and the only other alterations necessary at the rear are the substitution of two brake rods and the blanking off of the two rearmost servo cylinders.
Time Taken for Converting_ Special attention has been paid to the problem of arranging the vacuumpiping and the tail and stop-light connections to obviate the need for extending the piping and Wiring to the rear of the tractor.
It is possible to convert the complete semi-trailer to a trailer in about three to four hours.
The unladen' weight of the Thornycroft tractor and Tasker semi-trailer is just under 6i, tons, whilst the loading height with the semi-trailer is 4 ft. 114 ins, and with the trailer 4 ft. 5 ins.