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ROAD AND WORKSHOP by HANDYMAN
Page 64
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Misuse of Trailer Air-brake Hand Control
IN a previous article we described how .1. a 10-ton semi-trailer, equipped with foot-controlled vacuum brakes only, developed tail swing caused by a lack of thought in loading overlength steel bundles—and how on a maximum capacity outfit with air brakes this swing could have been held in check by the use of the air-brake hand control. The value of this hand-operated valve lies in the fact that. it provides gradual control in both application and release. This ability to control the trailing axles separately marks a big step forward in semi-trailer operation.
It can be stated with little fear of contradiction that the almost non-stop use of articulation right through the long winter of 1962-63 could hardly have been possible without the steadying influence of this hand control to trailed wheels. The swing mentioned in connection with the incorrectly loaded 10-ton trailer can also set up with any trailer on icy or snowbound roads. It can, all too often, end with that expensive incident "jack-knifing ".
However, this danger is now considerably reduced—if not removed altogether —by skilled use of the hand control and its drogue-like effect on the trailer. Nevertheless, even with such a contribution to vehicle safety and ease of handling, there are snags, or should I say, loopholes for misuse.
The remarkable degree of control now available can bring its own particular brand of expense. I refer now to the steering-column-mounted trailer brake handle, its ready, finger-tip control over four large brake assemblies, and the fact that the driver need do little more than move one hand a short distance to turn loose almost all the stopping power he needs. This is a wonderful feature, but unfortunately one prone to misuse with four drums instead of eight taking the full brunt of 24 tons at speeds up to 60 m.p.h.
So much so, that many engineers are now changing trailer brake drums at 40,000 miles or less—drums that are burned blue and cracked through every few inches of their circumference. This particular feature or theory had to be proved one way or the other to get to grips with this new expense. There was only one way to go about it, take a few rides in the passenger seat.
It is rather difficult to commend and yet criticize at the same time, and whilst acknowledging the undoubted skill and ability of each man at the wheel, the fact remained that whilst steering and driving axle drums were barely warm, the trailing axle drums were, in several instances, blazing hot.