Brake Tests

141 (b ) That the brake rigging be designed as far as practicable, so that the horizontal force from the cylinder to the truck will pass-through a line at a distance above the rail, corresponding to that of the resisting force of the car body. If the dead levers are anchored to the truck, there should be no vertical spacing between the top connections to the live lever and the pulling forces at the center plates on the car body, or if the dead levers are anchored to the car body, the anchor on the car should be the same distance above the rail as the top connection to the live lever. 1his is to avoid the lifting of the brake rigging during applications, which is a source of loss. If the relationship between “action and reaction between truck and car body is as outlined above, the effect on the former, so far as concerns the force action, or shifting of wheel weights will be the same irrespective of whether the dead levers are anchored to the truck or car body. Brake beams and heads should provide for a uni- form application of the pressure on the brake shoes. 307. (D) To insure a constant actual percentage of braking force, or what is frequently termed “constant brake rigging efficiency,” the brake levers should be of such lengths and the total truck leverage should be so proportioned, that the longitudinal movement of the levers will not bring about undesired or inefficient angles of the lines of action through the various pull rods, and that the angle of individual levers will not be such as to permit the shifting of badly worn pins in their respective holes, to change the leverage ratio when tires are turned or shoes are worn, and the brake beam hangers should be of such length and so located that the change in angle of hangers, due to shoe wear and tire turning, will not affect the normal shoe pressure (tlie pressure acting at an angle of 90 degrees from the wheel tangent, or in the direction of the center of the axle). The inclination of the hangers of inside hung brakes should conform to the requirements of the proper force distribution with respect to inertia effect in so far as such compensation does not introduce other- wise objectionable features. 308. (E) Uniform piston travel, irrespective of cylinder pressure, is a matter of importance in controlling heavy cars, because of the fact that the auxiliary reservoirs must be of a size suitable for a definite piston travel, and where the travel varies appreciably with the cylinder pressure, there will be an undesired loss in braking effect, when high braking forces are required or too high a braking force will be developed in a given time, when light applications are made at low speeds. 309. (F) It has been clearly demonstrated in laboratory and road tests, that the total shoe wear in dissipating a given amount of energy, is largely a function of shoe pressures and temperatures, rather than