A New Balanced-beam Extension Unit
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First Published Details of a Manchester Concern's Latest Conversion Sc! jor Trailing-axle Six-wheelers
FOR a considerable time the Truck and Tractor Appliance Co. (Manchester), Ltd., of Ashburton Road, Trafford Park, Manchester, has been marketing a set for converting fourwheelers into six-wheelers of the trailing-axle type. The company's latest design of conversion set, for the Britishbuilt Chevrolet 30-cwt. chassis, is being handled in Great Britain and Ireland by Spurling Motors, of The Hyde, Hendon, London, N.W.9, and is of the balanced-beam kind.
The *standard rear springs are substituted by two semi-elliptic springs 4 ft. 5 ins, long, each comprising 14 leaves 21 ins, wide and 1 in. thick. These springs are bracketed at the front end and shackled at " the rear end in normal fashion. To each .spring is held by II bolts a T-shaped east-iron chair, which extends downwards between the two faces of the cast-iron beam. Both are drilled to carry a cross-shaft of 1-&-in. diameter steel, extending the full width of the vehicle, and the chairs carry bronze bushes to permit oscillation in them of the shaft with the two rocking beams.
Over the cross-shaft is a distance tube of 2 ins, external diameter, with collar washers which butt against the Amer faces of the beams. These can, therefore, oscillate upon their central fulcrums, which are lubricated from beneath by screw cups.
The standard Chevrolet back axle is retained and, like the trailing axle, is held to the beams by cast-iron spherical bearings of 6 ins. outer diameter, these being each held between two east-iron collars which, in turn, are fixed in position by two bolts. The trailing axle is of 2i-in. solid steel bar, turned to a diameter of 21ins, to take the spherical bearings.
The driving-axle brake drums and shoes are retained and drums of 15iins. diameter and 3 ins, effective width are fitted on the trailing axle, a single shoe, with a brake-facing length of 3 ft. 10-4. ins., being fitted in each drum. This gives a friction area on the trailing-wheel brakes of 281.25 sq. ins., so that, with the standard Chevrolet equipment on the other four wheels,an aggregate friction area of 722 sq. ills. is obtained.
The brake torque is conveyed to the balanced beams by means of flanged bolts fixed to the back plates; the bolts extend for a few inches along the beams and are held to them by east-iron basses bolted through the beams themselves. The bolts may turn in the bosses and are allowed just sufficient lateral play to provide for the movement resulting from articulation, as permitted by the spherical hearings. A Dewandre vacuum cylinder is mounted on the off side of the engine and linked up to the induction system in the normal manner, and pulls by means of a cable upon the foot-brake pedal, from which the braking power is conveyed through the existing crossshaft and the compensator mounted on the driving-axle case. So that the trailing wheels will be braked along with the other four wheels when the pedal'is depressed, an extra lever is fitted to each foot-brake camshaft on the driving axle, and from this lever an enclosed cable transmits the power to each trailiug-wheel brake. The cable can be simply adjusted at either end, further adjustment being provided by a choice of three holes drilled on the front-end lever above referred to. The handbrake arrangement is undisturbed but for a step in the camshaft, so that it shall clear the front of the balance beam on each side.
The cables employed, as well as the joints, seem to be amply strong for their work, and, with the Dewandre cylinder and large friction area, it
would seem that the braking problems common with this type of vehicle have been boldly tackled. A particularly good point is the use of enclosed cables for the trailing-wheel brakes, this definitely preventing trouble due to articulation.
The bogie-axle centres are at a distance of 3 ft. 5 ins., this bringing the wheels as far apart as is practicable. As one of our illustrations shows, good articulation is obtained without stress on frame or components.
The price for supplying the parts and carrying out the conversion is £105.