How To Replace Air Brake Chambers
1. CAGE SERVICE SPRING. Park your truck or trailer on a level surface, chock the wheels and apply the parking brake. Position a locking pliers against the mounting housing of the failed air chamber and securely clamp it on the pushrod to prevent movement. Release the parking brakes.
2. CAGE PARKING SPRING. Remove the caging tool, also called a T bolt, from the storage tube on the Brake chamber . Remove the plastic inspection plug from the front of the spring-brake’s dome, or pressure cap. Shine a light inside the dome to locate the spring’s caging-tool hole. Insert the tool into the hole and turn it slightly until the T end hooks into the spring’s corresponding notches. Slip a flat washer over the tool’s bolt end and thread on a nut until it rests against the washer. Do not tighten the nut with a wrench unless you’re unable to use the vehicle’s air pressure for the caging process. When the spring is fully caged, the bolt should protrude about 31/4 inches from the dome. If air pressure is unavailable, you’ll need to crank down the nut with a wrench. In this event, do not exceed 35 pounds-feet of torque once the spring is caged. Reapply the parking brakes.
3. REMOVE AIR HOSES. (This procedure is unnecessary if you’re simply installing a new service diaphragm or mounting housing.) Mark the hoses to ensure proper reassembly, then loosen and remove them. Often the hoses will have a swivel fitting at one end and a crimped-on pipe fitting at the other. Remove both hoses at their swivel fittings. If either of these fittings is permanently bonded with corrosion, however, cut and replace the attached hose.
4. REMOVE SPRING-BRAKE CHAMBER. (This procedure is unnecessary if you’re replacing the mounting hosing and spring brake chamber.) Loosen the clamp holding the spring brake chamber to the mounting housing and tap it free with a hammer. Lift the chamber out of the clamp.
5. REMOVE MOUNTING HOUSING. (This and the following procedure are unnecessary if you’re only replacing the spring-brake chamber.) Pull the pin(s) connecting the pushrod clevis to the slack adjuster. Remove the nuts holding the mounting housing to the axle bracket. Use a steel brush to scrub accumulated corrosion and dirt from the bracket’s mating surface, then apply a coat of rust-inhibiting paint.
6. PREP AND INSTALL NEW MOUNTING HOUSING. While the old service spring is still caged, measure the pushrod length between the clevis and the outer surface of the mounting housing. Cage the new service spring by placing it on the floor – open side down – and standing on the housing while attaching a locking pliers to the pushrod. A jam nut should be installed on the new pushrod. Spin the nut down near the housing’s surface. Cut the pushrod so its length matches that of the old one. Use the jam nut to open any damaged pushrod threads. Install a new clevis and secure it with the jam nut. Mount the housing to the axle bracket and torque the nuts to the manufacturer’s specs. Connect the clevis and slack adjuster, and make sure they form a 90-degree angle when fully applied.
7. PREP AIR CHAMBER MATING SURFACE. (This and the following procedure are unnecessary on sealed chambers or complete kit replacements.) Inspect the mating surface of the chamber being reused. Use a steel brush or Emory cloth to scrub accumulated corrosion and dirt from the mating surface. Always replace clamps, bolts and diaphragms that have been in service more than a month, regardless of their appearance. These items are cheap and not worth the risk of failure.
8. INSTALL SPRING BRAKE CHAMBER. Loosely connect two band-clamp halves with one bolt. Lay a new diaphragm bowl-like inside the spring-brake chamber’s open end. Keeping the diaphragm in place with your fingertips, center the chamber on the mounting housing. Drape the clamp over the top of the chambers’ mating surface and gently tap it down. Repeat the procedure with the clamp’s bottom half and thread in its second bolt. Rotate the chamber for optimum access to the air-hose ports and fittings. Closely inspect the clamp to ensure it’s properly positioned all around the chamber, then tighten the bolts equally – moving from one to the other – until the clamp ends are 1/4 to 1/2 inch apart. Apply no more than 25 pounds-feet of torque to them.
9. APPLY AIR, UNCAGE AND LISTEN. Brush a thin coat of thread sealer on each end of your hose fittings and attach them to the proper ports. Release the parking brake and remove the caging tool from the air chamber’s dome. With an assistant using the brake pedal to apply 80 to 100 pounds of air pressure, remove the locking pliers from the pushrod. Listen for leaks. Lacking a helper, you can squirt soapy water on the mating surface then apply pedal pressure. Any leak will quickly generate a lot of bubbles. If the diaphragm hasn’t sealed, you’ll need to repeat steps 1, 2 and 8, locating the trouble spot in the process. Finish by installing the dome’s dust cap and securing the air hoses with plastic ties so they don’t rub against any hard surfaces.
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