Drum Brake System: Service and Repair

Fig. 1 Drum Brake Assembly.:

Fig. 2 Drum Brake Assembly.:

REMOVAL

1. Raise and support rear of vehicle, then remove tire and wheel assembly.
2. Remove brake drum. If brake lining is dragging on brake drum, back off brake adjustment by rotating adjustment screw. Refer to individual car chapter for procedure. If brake drum is rusted or corroded to axle flange and cannot be removed, lightly tap axle flange to drum mounting surface with a suitable hammer.
3. Install suitable wheel cylinder clamp over ends of wheel cylinder to retain pistons in bore.
4. On type 1 brakes, Fig 1, remove parking brake lever retaining clip.
5. On both types, Figs. 1 and 2, remove adjuster lever spring, primary and secondary shoe return springs using a suitable pair of brake spring pliers.
6. Remove shoe guide plate, if equipped and adjuster cable and guide plate.
7. Using suitable tool, compress hold-down springs, then remove spring retainers, hold-down springs and pins.
8. Separate springs and remove from backing plate.
9. On type 2 brake, disengage parking brake lever from secondary shoe.
10. On all types, remove parking brake lever from cable.
11. Separate all components from brake shoes.
12. Clean dirt from brake drum, backing plate and all other components. Do not use compressed air or dry brush to clean brake parts. Many brake parts contain asbestos fibers which, if inhaled, can cause serious injury. Clean brake parts with a water soaked rag or a suitable vacuum cleaner to minimize airborne dust.

Brake Adjustment Gauge:

INSTALLATION

1. Lightly lubricate backing plate shoe contact surfaces with suitable brake lube.
2. On type 1 brakes, assemble parking brake lever to secondary shoe and secure with spring washer and retaining clip. Crimp ends of clip with suitable pliers. On type 2 brakes, engage parking brake lever tang with secondary shoe.
3. Position brake shoes on backing plate, primary (short lining) shoe facing front of vehicle and secondary (long lining) facing rear. Secure brake shoes with hold-down springs, pins and retainers.
4. Install parking brake link and spring between shoes.
5. Loosen parking brake adjustment nut, then install parking brake cable on parking brake lever.
6. Install shoe guide plate and adjuster cable eyelet on anchor. Ensure adjuster cable crimp faces out.
7. Ensure parking brake link is properly positioned between brake shoes and wheel cylinder links are engaged in shoe web.
8. Using suitable brake spring pliers, install primary return spring from brake shoe to anchor, then secondary return spring from brake shoe to anchor.
9. On all types, remove wheel cylinder clamp installed during removal of brake shoes.
10. Tighten adjuster screw assembly to thread limit and back off 1/2 turn.
11. Install adjuster screw assembly between shoes. Ensure toothed wheel is on secondary shoe side. Adjuster screw assemblies are stamped R (right) and L (left). To ensure proper adjuster operation, they must be installed on their respective sides.
12. Hook adjuster cable hook into adjuster lever hole, then position adjuster spring hook in large hole in primary shoe web. Using suitable brake spring pliers, install adjuster spring in adjuster lever hole.
13. Ensure adjuster cable is properly seated in cable guide, then pull adjuster lever, cable and adjuster spring down and towards the rear, engaging lever pivot hook in the large hole of secondary shoe web.
14. After installation, check adjuster operation by pulling adjuster cable between cable guide and adjuster lever towards secondary shoe sufficiently to lift adjuster lever past one tooth on adjuster screw assembly. The adjuster lever should snap into position behind the next tooth, then upon release of adjuster cable, rotate toothed wheel one notch. If operation is not satisfactory, recheck installation.
15. Ensure brake shoe upper ends are seated against anchor pin and shoe assemblies are centered on backing plate. If not, back off parking brake adjustment.
16. Using suitable brake drum to shoe gauge, Fig. 3, measure brake drum inside diameter. Adjust brake shoes to dimension obtained on outside portion of gauge using adjuster screw.
17. Install brake drum, wheel and tire assembly.
18. If any hydraulic brake connections have been opened, perform system brake bleeding procedures.
19. Adjust parking brake. Refer to individual car chapter for procedures.
20. Inspect all hydraulic lines and connections for leakage and repair as necessary.
21. Check master cylinder fluid level and replenish as necessary.
22. Check brake pedal for proper feel and return.
23. Lower vehicle and road test. Do not severely apply brakes immediately after installation of new brake linings or permanent damage may occur to linings, and/or brake drums may become scored. Brakes must be used moderately during first several hundred miles of operation to ensure proper burnishing of linings.