DESCRIPTION
Brake system is hydraulically actuated using a tandem master cylinder and a Master Vac power brake unit. Front brakes are single piston, floating disc type. Rear brakes are leading-trailing, shoe/drum type. Drum brake are actuated by dual piston wheel cylinder. Parking brake is cable and lever operated, actuating shoes of rear drum.
ADJUSTMENT
PEDAL HEIGHT
Pedal height is measured from top of pedal pad to floor, should be 5.9-6.3". If adjustment is required, disconnect battery ground cable and stop lamp switch wiring harness. Remove stop lamp switch from bracket, then rotate master cylinder push rod until proper pedal height is obtained. Install stop lamp switch, then adjust clearance between switch housing (not actuating pin) and brake pedal tab to .02-.04". Tighten lock nuts and connect stoop lamp switch wiring harness.
FRONT DISC BRAKE PADS
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| Fig. 1 Assembled View of Rear Drum Brake Assembly |
Disc brakes are self-adjusting.
REAR BRAKE SHOES
Rear brake have a self-adjusting mechanism. No in-service adjustment is required. Initial adjustment may be necessary after changing brake lining. Pull adjuster mechanism out of star. Rotate star until shoes just contact drum. Final adjustment will be accompanied with self-adjuster mechanism.
PARKING BRAKE
Apply parking brake two notches from fully released position. Loosen equalizer check nut and adjust front jam nut until a light to moderate drag is felt when rear wheels are rotated forward. Tighten nuts securely, release parking brake lever, and ensure no drag is present.
HYDRAULIC SYSTEM BLEEDING
NOTE - Make sure engine is running while bleeding brakes. This will prevent damage to push rod.
Attach a bleed tube to wheel cylinder bleeder screw and immerse opposite end of tube in a container partially filled with brake fluid. Open bleeder screw 3/4 turn, depress pedal, close bleeder screw before bottom of pedal stroke, and allow pedal to return slowly. Continue operation until no air bubbles are seen in discharged fluid. Bleed wheel cylinder closest to master cylinder first, then repeat procedure at remaining cylinders, ending with cylinder furthest from master cylinder.
REMOVAL & INSTALLATION
FRONT DISC BRAKE PADS & BRAKE CALIPER ASSEMBLY
Removal - Raise and support vehicle. Remove tire and wheel. Take out caliper pin stops and remove stops. Remove caliper off support, take out stop plates, then suspend caliper from frame with wire. Remove pads and shims. Mark pad location for reassembly, if necessary. Separate anti-rattle spring from support.
Inspection - Replace disc pads when thickness is reduced to .039" (1 mm). Always replace pads in axle sets. Check caliper, supports and adaptors for distortion or cracking. Inspect inside caliper cavity for leaks. Replace any parts found defective.
Installation - To install, reverse removal procedures and note the following: Original pads must be installed according to index marks. Install pads to support with wear indicators facing LOWER SIDE. Make sure brake lubricant is applied to sliding portion of caliper
FRONT DISC BRAKE ROTOR
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| Fig. 2 Exploded View of Front Disc Brake Atty |
Removal - Raise and support vehicle. Remove tire and wheel. Remove caliper assembly. Remove grease cap, nut, and outer bearing. Pull hub and rotor assembly from vehicle, it is not necessary to separate hub and rotor, except to replace either component.
Inspection - Adjust all play out of wheel bearings and inspect rotor runout using a dial gauge. If runout exceeds .005" (.13 mm), replace or resurface. Check parallelism at four or more points. Value obtained must not exceed .005" (.001 mm) in 360 degrees. Make all measurements at same distance from edge of rotor.
Installation - To install, reverse removal procedure and note the following: Adjust wheel bearings.
REAR BRAKE SHOES
Removal - Remove tire and wheel. Remove tension from parking brake cable, remove retaining screws and remove brake drum. NOTE - Mark drum for reassembly reference. Remove return springs, hold-down springs, and self-adjuster assembly. Separate primary and secondary brake shoes, adjuster mechanism, return spring, and parking brake strut. Separate brake lever and rear cable, and remove lever from secondary shoe.
Installation - Install parking brake lever to secondary shoe and rear cable to lever. Connect brake shoes together with return spring and place adjuster screw into position, making sure star wheel is nearest secondary shoe. Install parking brake strut with spring on primary shoe end, then fit shoes to wheel cylinder push rods. Install hold-down springs, self-adjuster assembly, and return springs.
WHEEL CYLINDER
Removal - With brake drum removed, disconnect brake shoe return springs. Disconnect hydraulic line and bolts retaining cylinder to backing plate. Disengage cylinder push rod(s) from brake shoe(s) and remove cylinder.
Installation - Reverse removal procedure and bleed hydraulic system.
MASTER CYLINDER
Removal - Disconnect battery ground cable. Disconnect hydraulic lines at master cylinder and cover ends to prevent entry of dirt. Remove bracket bolt at front end of cylinder, and nuts retaining cylinder to power unit, then remove master cylinder and gasket from power unit.
Installation - Reverse removal procedure, bleed hydraulic system and adjust pedal height if necessary
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| Fig. 3 Master Cylinder Reservoir, Body and Piston Assembly |
POWER BRAKE UNIT
Removal - Disconnect battery ground cable. Disconnect hydraulic lines at master cylinder and cover ends to prevent entry of dirt. Remove bolts attaching bracket to master cylinder and fender and remove bracket. Disconnect vacuum line at power unit and place out of way. Disconnect brake pedal return spring and push rod. Remove nuts attaching power unit to firewall and remove power unit and master cylinder as an assembly.
Installation - Reverse removal procedure, bleed hydraulic system, and adjust pedal height if necessary.
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| Fig. 4 Exploded View of Power Brake Assembly |
OVERHAUL
FRONT DISC BRAKE CALIPER
Disassembly - Remove flex hose from caliper. Using pointed, but blunt instrument, remove seal from caliper. Place a block of wood between piston and caliper cavity wall, then apply enough compressed air pressure to force piston from cylinder.Remove and discard piston ring seal.
Installation - Replace dust seal and piston seal. Check cylinder bore for wear, scuffing or corrosion. Inspect cylinder piston for damage or wear. Never attempt to refinish piston. Replace any parts found defective.
Assembly - Lubricate piston seal and insert into caliper bore. Carefully insert piston into caliper assembly. Install dust seal to piston and caliper. Fit seal ring into dust seal.
WHEEL CYLINDER
Disassembly - Remove boots from cylinder ends. Remove pistons and cups. Remove expander springs, if equipped.
NOTE - Front wheel cylinder pistons and cups are services as an assembly
Cleaning & Inspection - Clean all parts in clean brake fluid. NOTE - Do not use mineral based solvents. Impact cylinder bore and pistons for rust, corrosion, or other damage; replace parts or cylinder as necessary. Measure clearance between piston and cylinder bore; if clearance exceeds .006", replace wheel cylinder assembly.
Reassembly - Lubricate cylinder bore with clean brake fluid. Install spring expander into bore, then install new cups with flat surfaces toward inside. NOTE - Do not lubricate pistons or cups before installation. Press new boots onto cylinder.
MASTER CYLINDER
Disassembly - Remove reservoir caps, plates and strainers and drain brake fluid. Place cylinder in a vise and remove reservoirs. Remove connector bolt, connector and gaskets from rear outlet, then withdraw end plug, gasket, check valve, return spring and spring seat. Remove check valve assembly from front outlet. Push in on primary piston, remove stop bolt and snap ring and remove primary and secondary piston assemblies.
Cleaning & Inspection - Wash all parts in clean brake fluid and dry using compressed air. Blow out all passages, orifices and valve holes. If slight rust is found, polish clean with crocus cloth or emery paper. Inspect cylinder bore for scoring, pitting, or other damage. Check clearance between pistons and cylinder bore. If greater than .006", replace cylinder. NOTE - Manufacturer recommends replacing rubber parts whenever master cylinder has been disassembled.
Reassembly - Lubricate cylinder bore and all parts with clean brake fluid, reverse disassembly procedure, and note the following: Ue all new gaskets and seals when reassembling. When reassembly is complete, bench bleed master cylinder as follows: Install plugs in all outlet parts of cylinder, fill reservoirs with clean brake fluid, and press in and out on primary piston until air bubbles are no longer seen in fluid.
POWER BRAKE UNIT
Disassembly - 1) Remove master cylinder reservoir and drain remaining brake fluid from cylinder. Scribe alignment marks on front and rear shells to assure reassembly in original position. Clamp flange of master cylinder in a vise with power unit up. Loosen push rod clevis lock nut and remove clevis lock nut, then remove push rod boot.
2) Place suitable wrench (J-9504) over rear shell mounting studs. Press down on wrench while rotating counterclockwise and remove rear shell, piston rod, power piston, return spring and spring retainer. Remove nuts and lock washers and separate master cylinder and power unit front shell, then remove and discard gasket.
3) Pry retainer off power piston and remove air silencer and filter, then remove rubber diaphragm from piston. Rotate power piston until push rod retainer slot is down, then press in on rod, allowing retainer to fall out of power piston. Remove push rod assembly and reaction disc. NOTE - Do not disassemble push rod assembly; if defective, replace complete assembly.
4) If rear shell is defective, pry out seal retainer and remove spacer and seal asembly. If front seal is defective, pry out retainer and remove seal. If vacuum check valve is defective remove using a twisting motion, then remove grommet.
Cleaning & Inspection - Clean all parts in denatured alcohol and blow dry with compressed air. NOTE - Do not clean parts with a mineral based solvent. Inspect inside surface of front adn rear shell for wear or damage. If slight rust is found on inside surface, polish clean with crocus cloth or fine emery cloth. Inspect all parts for cracks, nicks, distortion or other damage and replace as necessary.
Reassembly - Reverse disassembly procedure and note the following: Apply a coat of silicone grease to parts before installation. When assembling front shell to rear shell, ensure marks made at disassembly are aligned, when reassembly is completed, remove master cylinder from power unit. Place suitable gauge (J-24568) over piston rod so that legs rest on master cylinder mounting surface. Piston rod should touch cutout portion of gauge. If rod must be adjusted, hold rod at serrated portion and turn threaded end. NOTE - Push rod must be bottomed in power unit before making adjustment.
