Drum Brake System: Adjustments

Fig. 5 Brake adjustment with gauge:

Some models use a new front and rear brake backing plate which omits the adjusting slot for manual brake adjustment. The backing plates have a partially stamped knock-out slot for use ONLY when the brake drums cannot be removed in a normal manner. The open slot is then covered with a rubber plug as used in the past to prevent contamination of the brakes.
When servicing a vehicle requiring a brake adjustment, the metal knock-out plugs should NOT be removed. Rather the drums should be removed and brakes inspected for a malfunction.
Although the brakes are self-adjusting, an initial adjustment will be necessary after a brake repair, such as relining or replacement. The initial adjustment can be obtained by the new procedure which follows:
1. Use the brake shoe adjustment gauge shown in Fig. 10 to obtain the drum inside diameter as shown. Tighten the adjusting knob on the gauge to hold this setting.
2. Place the opposite side of the gauge over the brake shoes and adjust the shoes by turning the adjuster screw until the gauge just slides over the linings. Rotate the gauge around the lining surface to assure proper lining diameter adjustment and clearance.
3. Install brake drum and wheel. Final adjustment is accomplished by making several firm reverse stops, using the brake pedal.

Fig. 5 Rear Drum Type Brakes:

SELF-ADJUSTING BRAKES
These brakes, Fig. 11 have self-adjusting shoe mechanisms that assure correct lining-to-drum clearances at all times. The automatic adjusters operate only when the brakes are applied as the car is moving rearward.
Although the brakes are self-adjusting, an initial adjustment is necessary after the brake shoes have been relined or replaced, or when the length of the star wheel adjuster has been changed during some other service operation.
Frequent usage of an automatic transmission forward range to halt reverse vehicle motion may prevent the automatic adjusters from functioning, thereby inducing low pedal heights. Should low pedal heights be encountered, it is recommended that numerous forward and reverse stops be made until satisfactory pedal height is obtained.
If a low pedal condition cannot be corrected by making numerous reverse stops (provided the hydraulic system is free of air) it indicates that the self-adjusting mechanism is not functioning. Therefore, it will be necessary to remove the brake drum, clean, free up and lubricate the adjusting mechanism. Then adjust the brake, being sure the parking brake is fully released.