Vehicle Brake Performance Evaluation

An effort was made to evaluate accurately truck air brake performance balance at low application pressures by means of comparing drum temperatures. This procedure produced excellent results, and is a fast, practical method for evaluating brake performance of combination vehicles. The drum, hub, and wheel assemblies used in this evaluation were all the same type and weight. The s-cam used was a 16-1/2 X 7 in. and the wedge was 15 X 7 in. Mixed combinations of these types were tested.

It was found that s-cam brakes are more effective when used on drive axles than when used on trailing axles. A tractor protection valve with a built-in pressure increase of 33% to the trailer brakes was installed to compensate for the more effective drive axle brakes and this provided the desired braking balance.