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Mastiff six-wheeler by Primrose
Page 48
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• Six-wheeler versions of the BMC Mastiff 16-ton range of trucks are now available and can be ordered through British Leyland's truck and bus division, These three-axle models will be conversions to the four-wheelers by Primrose Third Axle Co. Ltd., Blackburn, Lancs, which has similar manufacturing arrangements with Seddon. The conversion has a list price of £689 in standard form which is added to the basic price of the Mastiff making the total price for the complete chassis about £3,500.
With the conversion, the Mastiff is plated for 22 tons gross weight, except for a short-wheelbase model which is limited to 20 tons. All are single-drive models.
Wheelbases of 19ft 5in., 17ft 4in. and 14ft 3in. are offered, these being based on the 17ft 3in., 15ft 2in. and 12ft 1in. wheelbase Mastiff models. They allow body lengths of 29ft 6in., 26ft and 20ft respectively although when the shortest wheelbase is ordered as a tipper, the maximum recommended body length is 18ft 3.5in. To give adequate strength for the higher loads, the Primrose conversion includes extending and sleeving the chassis with 12in. deep, 0.25in. thick pressed-steel channels for its whole loadcarrying length. Cross-members span the full depth of the frame's side-members.
A four-spring balance-beam suspension is used for the tandem bogie, using shackle pins and spring brackets from the Mastiff design. To assist traction in slippery conditions, Primrose offers an air bellows which temporarily imposes extra weight on the driving axle and lifts the trailing axle.
The brakes of the trailing axle are simple cam-expanded units, 7in. wide by 15.5in. diameter as on the Mastiff's driving axle. The actuating diaphragms are piped from the Westinghouse load-sensing valve linked to the driving axle so there is still a split between the front and rear brakes.