Self-tracking, trailing third axle
Page 48
If you've noticed an error in this article please click here to report it so we can fix it.
• Third axle conversions in which a selftracking axle is added behind the driving axle of a four-wheel goods vehicle are now available from Primrose Third Axle Co. Ltd. Primrose conversions have previously had the self-tracking axle ahead of the driving axle. With the new design less cost is involved where a long body is to be employed as repositioning of the driving axle is not required.
Two versions of the latest conversion system are available. In one, the added axle has leaf-spring suspension linked to that of the driving axle through load-compensating rocker beams. In this case the chassis frame is flitched for almost its full length as well as being extended to the rear. A conversion of this type adds £824 to the chassis price when 10.00-20 tyres are fitted.
As an alternative, the self-tracing axle can have air suspension when it is located by two quarter-elliptic leaf springs and a Panhard rod. Load compensation between the axles and the correct braking distribu tion are automatically taken care of by a pair of Westinghouse load-sensing valves. There are fewer alterations with the air suspension and the conversion price is £38 less than with the leaf springs.
With the air-sprung version, extra load can be put on the driving axle temporarily to help traction in difficult conditions and this is done by exhausting air from the bellows. This can also be done with the four-spring bogie by using the Primrose Hi-lift load-transfer system which adds £105 to the price.
The self-tracking axle used by Primrose is an adaption of the Italian Ceschi design.