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The 4-wheel chassis was supplied by J Brockhouse & Co Ltd, West Bromwich, and is the same as that supplied to the Royal Air Force for carrying signalling equipment at speed over rough country. Each wheel is independently sprung by means of a torsion bar. These bars are about 5’ long and 1 1/8” diameter. They are made from silico manganese spring steel, oil-hardened and tempered, with an ultimate tensile strength of 85-100 tons per square inch. Each bar is encased in a tube which extends the whole width of the chassis and is anchored to the chassis by a splined sleeve. The other end passes through a bearing and is then splined onto a tubular crank arm (the oscillating arm), on the end of which is mounted the stub axle for the wheel. The load on the wheel is taken up by the twisting of the torsion bar, which provides a very smooth, completely adjustable system of springing. It also allows the roughest of grounds to be traversed with the minimum disturbance to the level of the body.

The two front wheels are mounted on a turntable with freedom to rotate 45 degrees on either side of the dead ahead position. The drawbar is attached to this turntable, and terminates in a steel coupling eye.

MoT regulations limit the speed of a 4-wheeled trailer to 20mph, and also required that independent control of the trailer brakes, where positive control by the driver of the towing unit is not provided (over-run brakes not being permitted on heavy trailers). The independant control is required on these trailers as it was not known what towing vehicle would be available. To this end a brakeman’s cabin is provided at the front off-side of the body. There is a brake lever in this cabin, and also one on the near-side chassis member (this one for use as a parking brake when manoeuvring by hand). The brakes themselves are Lockheed hydraulic types, working independently on all four wheels.

When the vehicle has arrived on site, the road wheels are replaced by heavy steel feet (normally carried in the body). These feet serve two purposes: they prevent the tyres from decay, and allow the weight (5 tons 14cwt) to remain on the axles, so preventing the twisting that would occur if the chassis was packed. The operation of changing the wheels can be done by one man.

Chassis of MAX12

General Design
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Telephone Equipment

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