8/15/2023 0 Comments Pushrod and slack adjuster“Recognizing the need for vastly improved driver air brake education, particularly in the United States,” the company’s “Air Brake Interactive Quick Study” courses function well for individual operators. Dangerously undependable brake performance will result from distorted drums, weak return springs, improper lining, poor adjustment, or grease or dirt on the lining.ĭrums must never be turned or worn beyond the manufacturer’s specification.“We’ve addressed the issue of not adjusting auto-slacks countless times in several of our programs,” Duross said. Drums worn thin will build up heat too quickly. The thickness of the drums determines the amount of heat they are able to absorb and dissipate to the atmosphere. The brake linings generate heat from friction with the brake drum surface. The twisting action of the brake cam shaft and ‘S’ cam forces the brake shoes and linings against the drums. The brake linings also lose their effectiveness with overheating. Brake lining must give uniform output of brake effort with minimum fade at high temperature.įading or a reduction in braking effort occurs when the heated drums expand away from the brake linings. The material used depends on the braking requirements of the vehicle. A front axle assembly has the brake chamber and slack adjuster mounted on the backing-plate because of the steering action.īrake lining material is attached to the shoes. The diagram below illustrates a common type of brake assembly used on truck rear axles and trailer axles. NOTE: Detailed brake adjustment procedures are outlined in Section VI. Automatic slack adjusters must be checked regularly to ensure that correct adjustment is being maintained. Some systems have automatic slack adjusters which adjust automatically to compensate for brake lining wear, thus maintaining the correct clearance between the brake lining and drum. The more often the driver checks the ‘slack’, the less the probability of brake failure Vehicles rarely ‘lose’ their brakes because of loss of air it is usually a loss of adjustment. Some slack adjusters use a spring loaded internal check ball to lock the adjustment. A locking device, which may be a spring loaded collar over the head of the adjusting bolt, must be depressed when the wrench is slipped over the bolt head. When the brakes are fully applied, the angle between the push rod and the arm of the slack adjuster should be no more than 90 degrees (a right angle) On this type of slack adjuster, the adjusting worm bolt is turned until the brake linings touch the drums and then backed off, normally 1/4 to 1/2 a turn. The diagram illustrates a common type of slack adjuster, showing the worm adjusting gear. If this condition is allowed to occur, the brakes will not be effective at all. If too much slack develops, the diaphragm will eventually ‘bottom’ in the brake chamber. If the slack adjusters are not adjusted within the limitations, effective braking is reduced and brake lag time is increased. This slack occurs as the brake linings wear. When the air is exhausted, the spring in the brake chamber returns the diaphragm and push rod to the released position.Īs indicated by its name, the slack adjuster is also the means of adjusting the ‘slack’ or free play in the linkage between the push rod and the brake shoes. This converts the pushing motion of the push rod from the brake chamber to a twisting motion of the brake camshaft and ‘S’ cams. The push rod is connected by a clevis and pin to a crank arm type lever called a ‘slack adjuster’. The air pushes against the diaphragm and the push rod. Air pressure is fed through an inlet port. A brake chamber is usually mounted on the axle, near the wheel that is to be equipped for braking. If the diaphragm is completely ruptured, brakes become ineffective.įront brake chambers are usually smaller than rear brake chambers because the front axles carry less weight than the rear axles. If a leak occurs in the diaphragm, air is allowed to escape, reducing the effectiveness of the brake chamber. The force exerted by this motion depends on air pressure and diaphragm size. Air pressure pushing against the diaphragm causes it to move away from the pressure, forcing the push rod outward against the slack adjuster. Maintenance and Servicing of the Air Brake SystemĪ brake chamber is a circular container divided in the middle by a flexible diaphragm.Schedule SX, Off-Highway Trailer with Spring Brake.L-75 Off-Highway System, Combination with Schedule X Trailer.Manually Operated Trailer Supply Valves.Dual Control Valve and Reservoir System.
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