Pushrod and slack adjuster9/16/2023 ![]() ![]() ![]() ![]() Once properly installed, automatic slack adjusters should not need manual adjustment. It is not uncommon to find that the brakes on one or the other axle have been mistakenly backed off, creating a serious safety hazard.Īfter adjusting, verify that there is sufficient clearance by again pulling or prying on the slack adjuster arm, and re–measuring the free stroke, remember that ½ inch is ideal.Īutomatic slack adjusters are entirely different than the manual types. It is common, especially on tandem axle units, for the adjusting bolts on one axle to adjust in one direction, while the other axle requires an opposite turn. Be sure the locking sleeve re–engages the bolt so that the adjustment will not back off. If the brake has no dust shields, or if you can see the brake shoes and linings through an inspection slot, you can visually verify that the linings have contacted the drum.īacking off the adjusting bolt about 1⁄ 3 of a turn should establish correct running clearance between the lining and drum. This indicates that the brake linings have contacted the brake drum. Once the proper direction is established, continue turning until solid resistance is met. The adjusting bolt is being turned in the wrong direction. If when turning the adjusting bolt, the slack adjuster is pulling the pushrod out of the chamber, stop. The push rod and the slack adjuster arm should never move away from the brake chamber while turning the adjusting bolt. If you are turning in the right direction, the cam will rotate in the same direction that it would if the brakes were being applied, as shown by the arrow on the cam end in the diagram below. The camshaft will rotate slightly as the bolt is being turned. With a wrench of the proper size, usually a 9/!^ inch, depress the locking sleeve and turn the adjusting bolt while watching the end of the camshaft. Watch to ensure that you are tightening and not loosening the slack adjustment. Most manual slack adjusters have a spring–loaded locking sleeve that must be pressed in and held so the adjusting bolt can be turned.ĭepending upon the orientation of the slack adjuster, the correct direction to turn the adjusting bolt may be clockwise or counterclockwise. While checking air brakes look for other brake component wear and excessive play including: The difference between measurements is called the chamber applied stroke. ![]() Measure the distance between the mark and the face of the brake chamber.Apply and hold a full brake application (90 to 100 psi).With the engine off, make a series of brake applications to reduce the reservoir pressure to between 90 to 100 psi.With the brakes released, make a mark where the pushrod exits the brake chamber.The applied stroke method is the preferred method and is also a method recommended by commercial fleet maintenance supervisors. If the red marking on the pushrod (at the chamber face) is visible, it indicates that the brake is dangerously out of adjustment and it needs immediate attention. If the pushrod travel becomes excessive, the marking will show.ĭon’t wait until the red marking is exposed before adjusting the brakes. New air brake chamber pushrods have a marking (usually red) to indicate when brake adjustment must be done immediately. There are two methods of checking for correct adjustment, but the measurements that indicate the need for adjustment are different. Turn the engine off so that you can listen for air leaks. The air system should be at full pressure and the spring parking brakes released. Be sure that the vehicle is safely parked with the wheels blocked. However, brakes can still be adjusted very accurately with the wheels on the ground using one of the following methods. S–Cam Brake–Incorrectly Adjusted and Cold Brake Drumĭrivers seldom have the luxury of having the use of a pit and hydraulic jacks so that brake adjustment can be done with wheels off the ground. This could result in brake fade under moderate to heavy braking, or on a downhill. On long downgrades, the expansion of hot brake drums can cause a total loss of braking and result in a runaway.Įven incorrectly adjusted brakes may seem to work when brakes are lightly applied. If an unforeseen event required the driver to make a sudden stop, the brake chamber could bottom out, and braking power would be greatly reduced. Cast iron brake drums expand when heated, causing the air chamber to stroke further and further as the temperature rises. ![]()
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