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Twin-steer BigJ tractive unit

9th September 1966
Page 72
Page 72, 9th September 1966 — Twin-steer BigJ tractive unit
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rr WO chassis will provide the main interest on the stand of Guy Motors Ltd., at the Commercial Motor Show. These will be a twin-steer tractive unit for 32 tons gross train weight and a 26-tons six-wheeler designed for export markets which has automatic transmission and a new-design two-spring rear bogie. On another show chassis Guy will use MGM Spring Brakes to provide the secondary and parking brakes.

The Guy Big J was introduced at the last Commercial Show and there are to be five chassis from this range at this one. Completing the proposed exhibits there is to be a Guy Arab Mark V single-deck passenger chassis. Four of the Big Js on the Guy stand will have the Cummins V6 engine and one will be fitted with the latest Gardner 6LKXB, 180 b.h.p. unit. The new Gardner will be in the twin-steer tractive unit which is basically a Guy eight-wheeler with the rear bogie removed, the frame shortened and a 10-ton capacity hub-axle fitted.

Each front axle has a capacity of 5 tons and Hydrosteer power steering is fitted; the double-acting ram acts on the relay lever in the steering linkage. Braking on this new model is by a dual-circuit air-pressure system with the driving axle and the front axle on one circuit and an independent circuit to the second front axle. Multidiaphragmfactuators are fitted to both front axles and provide for the secondary system in conjunction with the auxiliary line to the semi-trailer; the hand brake is mechanical to the driving axle with air assistance.

Guy has never previously produced a two-spring rear bogie and the unit on the 26-ton-gross six-wheeler has been designed with poor road 'conditions in mind such as are often met in overseas markets. The axles have hypoid-bevel primary reductions at the centre and epicyclic secondary reduction in the hubs. The drive to the bogie enters the first axle and is transferred to the hypoid gears through spur gearing and then continues through the casing to the second axle centre. A third differential is included in the transmission line and this can be "lacked-out". Each of the driving axles is located in the chassis by three radius rods, two of which are set below the casings and one above. A cross tube carries the single semi-elliptic springs on each side and the ends of the springs are free to slide in their mountings.

Wheelbase of the show model will be 15 ft. 9.5 in. and it will have left-hand steering. A sleeper cab will be mounted on the chassis and another way in which the export characteristic of the vehicle will be illustrated is that Trilex cast-spoke wheels will be used.

Although the six-wheeler will have an SRM fully automatic transmission this is not specifically offered as an option by Guy because, unfortunately, Bristol Siddeley who had the licence to make this Swedish transmission unit gave it up two or three weeks ago. But Guy will be showing its interest in automatic transmission and no doubt will be offering this feature later.

With the use of MGM spring brakes— on a 30-ton gross four-wheel tractive unit— Guy has gone away from its usual practice on the Big J of having split circuits for brake operation. The brakes on this show model will be on a single circuit and this has been done because of the fail-safe characteristics of spring brakes. The MGM units provide for the secondary-brake requirement as well as parking and as usual with this type of fitting a "gated" hand control is provided. The spring brakes perform in exactly the same way whether the secondary or "parking" position is selected but in the former case the "auxiliary" line to the semi-trailer is pressurized through an inverter valve as air is exhausted from behind the holding-off springs.

The remaining two goods chassis to be exhibited by Guy will be a 20-ton gross sixwheeler and a 24-ton gross train weight two-axle tractive unit. Like the 26-ton sixwheeler and the 30-ton gross tractive unit these will have Cummins V6 9.63-litre engines but the 24-ton tractive unit will have the derated version giving 170 b.h.p. as against 192 b.h.p.

A feature of the 20-ton six-wheeler is that it will be fitted with a new-design heavy-duty hypoid-bevel double-drive rear bogie each axle of which has capacity of 8 tons. The leading axle carries a single helical-reduction gear train giving in effect double reduction to both axles and a lockable third differential is fitted. The 24-ton tractive unit will be used to illustrate the accessibility afforded to the engine when the floor is removed. Both the drivers and passengers seats are mounted on the floor panel and after taking these out the panel itself can be removed by unscrewing nine bolts.

Completing the exhibits there is to be the Guy Arab Mark V front-engined bus chassis which is sold as a single decker for export markets. The show chassis will be one of an order for the China Motor Bus Co. Ltd., Kowloon, Hong Kong, and has a 15 ft. wheelbase. The engine is a Gardner 6LX, the transmission a Daimler Diamatic fourspeed semi-automatic gearbox. A.J.P.W.


Locations: Kowloon

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