Usually, the biggest challenge is loosening the old slack’s grip on the S-camshaft. Without difficulties, slack adjusters can be swapped in less than 30 minutes, not counting time spent chasing parts or drinking coffee. The benefits of extended longevity are something to consider the next time a scale master directs you to a waiting inspection lane.ĥ.Ě well-greased 10-spline S-camshaft without the slack. This valve functions in the same manner as the treadle valve except that the handle is turned, rather than depressed, to operate the valve.“If proper maintenance is routinely done, there is no reason that a slack adjuster shouldn’t last as long as the vehicle it’s mounted to,” says Gary Ganaway at ArvinMeritor. 7-48) provides the operator with control of the trailing load at all times. The independent trailer control valve (fig. If cleaning does not remedy the malfunction, the valve must be replaced. This prevents moisture in the air system from causing corrosion and freezing of the valve. After cleaning, the internal parts should be lubricated with Vaseline before reassembly. Should the valve malfunction, it can be disassembled and cleaned. Maintenance of the treadle valve consists of periodic lubrication of the hinge and roller. Further depression of the treadle valve increases the forces above the diaphragm and correspondingly increases the delivered air pressure until a new balanced position is reached. This action allows the inlet valve to close but also keeps the exhaust valve closed, thereby obtaining a balanced position.
As the air pressure increases below the diaphragm, it overcomes the force above the diaphragm and the diaphragm raises slightly. Continued movement opens the inlet valve and air pressure from the reservoir flows through the valve and into the delivery lines to apply the brakes.
When the treadle valve is depressed, force is transmitted to the pressure regulating spring and diaphragm that is moved downward and contacts the exhaust valve and closes it. 7-47) controls the air pressure delivered to the brake chambers. In the following paragraphs we will discuss each valve in more detail. These valves are as follow:Ĭombined-limiting and quick-release valve These valves either apply or release airįrom the brakes and work together to ensure control and safe braking application.
There are numerous brake valves used in an air brake system. When the brakes are released, the brake shoe return spring pulls the shoes back to a DISENGAGED position. Friction of the brake lining against the drum stops the turning movement of the wheel. The movement of the cam forces the brake shoes against the brake drum. expanding the brake shoes so that the slack caused by brake lining wear is eliminated and the slack adjuster arm travel is returned to the correct setting. This action rotates the worm gear, camshaft, and cam. Turning the adjusting screw makes the brake adjustments necessary to maintain proper slack adjuster arm travel (shoe and drum clearance). The entire slack adjuster rotates as a lever with the brake camshaft, as the brakes are applied or released. Air pressure, admitted to the brake chamber when the brake pedal is depressed, moves the slack adjuster toward the position indicated by the dotted lines. 7-46) function as adjustable levers and provide a means of adjusting the brakes to compensate for wear of linings. The pushrod length should be adjusted so that the angle between the center line of the slack adjuster and the brake chamber pushrod is 90 degrees when the pushrod is extended to the center of its working stroke. adjust the brakes so that pushrod travel is as short as possible without the brakes dragging. Check the pushrod travel periodically, and when necessary'. When performing maintenance of the brake system, check the brake chamber alignment to avoid binding action. After the shoes reach the fully released position, the return springs acting on the diaphragm causes it to return to its original position in the chamber. When the pedal is released, air is forced from the brake chamber by the brake shoe return spring acting on the linkage. brake camshaft, and cam to apply the brakes. Because the yoke on the end of the pushrod is connected to the slack adjuster, this movement rotates the slack adjuster. When the brake pedal is actuated, air under pressure enters the brake chamber behind the diaphragm and forces the pushrod out against the return spring force. 7-45) converts the energy of the compressed air into mechanical force to operate the brakes.
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