FRONT DISC BRAKES
Disc brakes are not adjustable. They are, in effect, self adjusting during normal operation. For details on how the disc brakes operate, please refer to the operating principles found earlier in this section.
REAR DRUM BRAKES
See Figure 1
Normal adjustments of the rear drum brakes are automatic and are made during the reverse applications of the brakes. The following procedure should be used ONLY if the linings have been replaced.
- Raise and support the rear of the vehicle safely using jackstands.
- Using a punch and a hammer on the rear of the backing plates, knock out the lanced metal areas near the starwheel assemblies on each plate. The metal areas may already have been removed and covered with rubber adjustment plugs, if so remove the plugs by grasping and pulling with a pair of pliers.
After knocking out the lanced metal areas from the backing plate, the wheels must be removed and all of the metal pieces discarded, then the wheels should be reinstalled for adjustment.
- Insert a suitable brake adjustment tool such as J-4735 or equivalent, into the breaking plate slots and engage the lowest possible tooth on the starwheel. Move the end of the brake tool downward to move the starwheel upward and expand the adjusting screw. Repeat this operation until the wheels can JUST be turned by hand. This is a position immediately before the brakes lock.
The brake drag should be equal at both wheels.
- Back off the adjusting screws 24 notches (clicks). By the time you have backed off the adjustment 12 clicks, the brakes should have no drag. If a heavy drag is still present, the parking brake cable is likely in need of adjustment.
- Make sure both sides of the brakes are properly adjusted. When backing off the brakes on the other side, the adjusting lever must be backed off the same number of turns to prevent side-to-side brake pull.
- After the brakes are adjusted, install a rubber hole cover into each of the the backing plate slots. To complete the brake adjustment operation, make several stops while backing the truck to fully equalize the adjustment.
- Road test the vehicle.
BRAKE PEDAL TRAVEL
See Figure 2
The brake pedal travel is the distance the pedal moves toward the floor from the fully released position. On most vehicles covered by this manual it is not adjustable, but checking the distance will give an indication of system condition. Inspection should be made using 100 lbs. (445 N) of pressure on the brake pedal, when the brake system is Cold. On power brake equipped vehicles, be sure to pump the brakes at least 5 times to remove vacuum from the booster before making the check.
To check the travel, first measure the distance from the top of the released pedal to the bottom of the steering wheel, then depress the pedal (using 100 lbs. of force) and re-measure the distance. The difference between the 2 measurements (pedal travel) should be approximately 4 3 / 4 in. (120mm) for manual brakes or 2 1 / 2 in. (61mm) for power brakes.
If the pedal travel is excessive, check the pedal and the hydraulic brake system for wear or damage and repair, as necessary. If no damage can be found on early model vehicles adjustment may be possible. Check the pedal pushrod for an adjuster nut. If equipped with an adjustable pushrod and no damage or wear was found in the brake system, adjust the travel as follows:
- From under the dash, remove the pushrod-to-pedal clevis pin and separate the pushrod from the brake pedal.
- Loosen the pushrod adjuster locknut, then adjust the pushrod.
- After the correct travel is established, reverse the removal procedure and check for proper operation.