REAR DRUM BRAKES
The rear drum brakes on your vehicle are self-adjusting. The only adjustments necessary should be an initial adjustment, which is performed after new brake shoes have been installed or some type of service work has been done on the rear brake system.
After any brake service, obtain a firm brake pedal before moving the vehicle. Adjusted brakes must not drag. The wheel must turn freely. Be sure the parking brake cables are not adjusted too tightly. A special brake shoe gauge, Tool D81L-1103-A or equivalent, is necessary for making an accurate adjustment after installing new brake shoes. The special gauge measures both the drum diameter and the brake shoe setting.Vehicles Equipped with 7 in. (178mm) Brakes
Pivot the adjuster quadrant until the third or fourth notch from the outer end of the quadrant meshes with the knurled pin on the adjuster strut. Install the hub and drum.Vehicles Equipped with 8 in. (203mm) Brakes
Measure and set the special brake gauge to the inside diameter of the brake drum. Lift the adjuster lever from the star-wheel teeth. Turn the star-wheel until the brake shoes are adjusted out to the shoe setting fingers of the brake gauge. Install the hub and drum.
Complete the adjustment by applying the brakes several times. After the brakes have been properly adjusted, check their operation by making several stops from varying forward speeds.
FRONT DISC BRAKES
Front disc brakes require no adjustment. Hydraulic pressure maintains the proper pad-to-disc contact at all times. If for any reason the brake pressure changes, check the brake fluid level or pad width.Brake Pedal
The correct adjustment of the brake pedal height, free-play and reserve distance is critical to the correct operation of the brake system. These 3 measurements interrelate and should be performed in sequence.Brake Pedal Reserve
- Operate the engine at idle with the transmission in either PARK or NEUTRAL.
- Depress the brake pedal lightly 3 to 4 times.
- Allow 15 seconds for vacuum to replenish the booster.
- Apply the brake pedal until it stops moving downward.
- Hold pedal in applied position and raise engine idle to approximately 2000 rpm.
- Release the accelerator pedal and observe that the brake pedal moves downward as the engine returns to normal idle speed.
The additional movement of the brake pedal is the result of the increased engine manifold vacuum which exerts more force on the brake booster during engine rundown.
If the pedal does not move downward, check one or both of the following:
- Check the one-way valve between the brake booster and the manifold. This valve is usually white in color, and is found in-line with the vacuum hose, near the booster. Remove the valve, and blow air through both ends of it. If the valve functions properly, air will pass through in only one direction. If air passes through in both directions, or will not pass at all, the valve should be replaced.
- If the one-way valve is functioning properly, the rod length on the booster pump may be too long. To check and adjust this you will need to remove the master cylinder from the vehicle. Refer to the master cylinder procedure for more details. With the master cylinder removed, the rod length on the booster can be checked and/or adjusted. Refer to brake booster adjustment information for a detailed procedure.
See Figure 1
- Insert a slender, sharp pointed prod through the carpet and sound deadener to dash panel metal. Measure the distance to the center of brake pedal pad on the side of the pedal pad nearest the accelerator pedal.
- If the position of the pedal is not within specification, check brake pedal for missing, worn or damaged bushings, or loose attaching bolts, and replace if necessary.
- If pedal free height is still out of specification, check brake pedal, booster or master cylinder to be sure the correct components are installed. Replace components as necessary.
See Figure 2
- With engine running and the transmission in PARK or NEUTRAL, block the wheels and release the parking brake.
- Install brake pedal effort gauge 021-00001 or equivalent on the brake pedal.
- Secure steel measuring tape to the brake pedal. Measure and record the distance from the brake pedal free height position to the reference point which is at the 6:00 position on the steering wheel rim.
- With the steel tape hooked to the brake pedal, depress the brake pedal. Apply 25 lbs. (11.2 Nm) of load to the center of the pedal. Maintain the pedal load and measure the distance from the brake pedal to the fixed reference point on the steering wheel rim, which is parallel to the center-line of the steering column.
- If pedal travel is more than the maximum specification on vehicles with self-adjusting drum brakes, make several reverse stops with the vehicle, with a forward stop before each to adjust the brakes. If these several stop/start attempts do not work, try another series of stop/start.
- On self-adjusting drum brake vehicles, if the previous step did not bring the travel within specification, Remove the brake drums and visually check the adjuster. Check the brake lining for wear or damage. Replace any worn parts.
- If the previous step does not resolve the problem, check the brake pedal assembly for missing or loose attachments.
- If brake travel is still not within specification, bleed the brake system.