1. start

9. CAUTION: Proper precaution should be taken to prevent any asbestos that may be present in the brake system from becoming airborne. Removal of the brake drum should occur inside a sealed vacuum enclosure equipped with a HEPA filter or washed with water or solvent. Figure 75–1 A liquid soaking solvent, such as brake cleaner, should be used to wet the linings. The purpose of wetting the lining material while the drum is still on the vehicle is to prevent the possibility of asbestos from the lining becoming airborne. Asbestos is only hazardous when asbestos dust is airborne and is breathed in during brake system service.

12. Figure 75–2 Tinnerman nuts are used at the vehicle assembly plant to prevent the brake drum falling off until the wheels can be installed. These sheet-metal retainers can be discarded after removal. Continued

15. Figure 75–4 If the brake shoes have worn into the brake drum, the adjuster can be backed in after removing the access plug. After removing the plug, use another wire or screwdriver to move the adjusting lever away from the starwheel, then turn the starwheel with a brake adjusting tool, often called a brake “spoon.” (Courtesy of Allied Signal Automotive Aftermarket) NOTE: Be sure to reinstall the adjuster opening plugs. These plugs help keep water and debris out of the brakes.

21. Figure 75–8 A typical rusting backing plate shoe pad. This can cause the brakes to squeak when the shoes move outward during a brake application and again when the brake pedal is released. Continued

26. Figure 75–12 Cracked brake lining must be replaced.

28. Figure 75–13 Brake lining worn at the top edge near the anchor pin is one indication that the return (retracting) springs are weak. Continued

34. Figure 75–15 Exploded view of a typical wheel cylinder. Note how the flat part of the cups touch the flat part of the piston. The cup expander and spring go between the cups. Continued

36. Figure 75–16 Many wheel cylinders are bolted to the support plate (backing plate). The O-ring seal helps keep water and dirt out of the drum brake. Continued

37. Figure 75–17 (a) Some wheel cylinders are simply clipped to the backing plate. Continued

38. Figure 75–17 (b) This special tool makes it a lot easier to remove the wheel cylinder clip. A socket (1 1/8 in., 12 point) can be used to push the clip back onto the wheel cylinder. Continued

43. NOTE: Even though the wheel cylinder is not leaking, many brake experts recommend replacing or rebuilding the wheel cylinder every time new replacement linings are installed. Any sludge build-up in the wheel cylinder can cause the wheel cylinder to start to leak shortly after a brake job. When the new thicker replacement linings are installed, the wheel cylinder piston may be pushed inward enough to cause the cup seals to ride on a pitted or corroded section of the wheel cylinder. As the cup seal moves over this rough area, the seal can lose its ability to maintain brake fluid pressure and an external brake fluid leak can occur. Figure 75–18 When new, thicker materials are installed, the pistons and cups are forced back into the wheel cylinder and pushed through the sludge that is present in every cylinder.

47. NOTE: Many technicians preassemble the primary and secondary shoes with the connecting (lower retracting) spring as a unit before installing them onto the backing plate. Figure 75–20 Preassembly of the starwheel adjuster with its connecting spring often helps when reassembling a drum brake. Figure 75–21 Sometimes it is necessary to cross the shoes when preassembling the starwheel adjuster and connecting spring. (Courtesy of Allied Signal Automotive Aftermarket)

51. Figure 75–23 Notice that the brake shoe is not contacting the anchor pin. This often occurs when the parking brake cable is stuck or not adjusted properly. Continued

53. Figure 75–25 Place the gauge over the shoes and adjust the brakes until they contact the inside of the gauge. Continued

68. end