Description and operation

Brake system

Description

This vehicle is equipped with front disc brakes and rear drum brakes. The front disc brakes consist of single piston calipers and ventilated rotors. The rear brakes are dual brake shoe, internal expanding units with cast brake drums. The parking brake mechanism is cable operated and connected to the rear brake secondary shoes. Power brake assist is standard equipment. A vacuum operated power brake booster is used for all applications.

Two antilock brake systems are used on this vehicle.

A rear wheel antilock (rwal) brake system is standard. An all-wheel antilock brake system (abs) is available as an option.

Service warnings & cautions

Description

Warning: dust and dirt accumulating on brake parts during normal use may contain asbestos fibers from production or aftermarket linings. Breathing excessive concentrations of asbestos fibers can cause serious bodily harm. Exercise care when servicing brake parts. Do not clean brake parts with compressed air or by dry brushing. Use a vacuum cleaner specifically designed for the removal of asbestos fibers from brake components.

Follow practices prescribed by the occupational safety and health administration and the environmental protection agency for the handling, processing, and disposition of dust or debris that may contain asbestos fibers.

CAUTION: Never use gasoline, kerosene, alcohol, motor oil, transmission fluid, or any fluid containing mineral oil to clean the system components. These fluids damage rubber cups and seals. Use only fresh brake fluid or Mopar brake cleaner to clean or flush brake system components. These are the only cleaning materials recommended. If system contamination is suspected, check the fluid for dirt, discoloration, or separation into distinct layers. Also check the reservoir cap seal for distortion. Drain and flush the system with new brake fluid if contamination is suspected.

CAUTION: Use Mopar brake fluid, or an equivalent quality fluid meeting SAE/DOT standards J1703 and DOT 3. Brake fluid must be clean and free of contaminants.

Use fresh fluid from sealed containers only to ensure proper antilock component operation.

CAUTION: Use Mopar multi-mileage or high temperature grease to lubricate caliper slide surfaces, drum brake pivot pins, and shoe contact points on the backing plates. Use multi-mileage grease or GE 661 or Dow 111 silicone grease on caliper slide pins to ensure proper operation.

Brake pedal

DESCRIPTION

A suspended-type brake pedal is used. The pedal is attached to the pedal support bracket with a pivot pin and bushings. The booster push rod is attached to the pedal with a clip. The pedal, bushings, pivot pin and support bracket are all serviceable components.

OPERATION

The brake pedal is attached to the booster push rod. When the pedal is depressed, the primary booster push rod is depressed which move the booster secondary rod. The booster secondary rod depress the master cylinder piston.

Stop lamp switch

DESCRIPTION

The plunger type stop lamp switch is mounted on a bracket attached to the brake pedal support.

CAUTION: The switch can only be adjusted during initial installation. If the switch is not adjusted properly a new switch must be installed.

OPERATION

The brake lamp switch is used to for the brake lamp, speed control and brake sensor circuits. The brake lamp circuit is open until the plunger is depressed. The speed control and brake sensor circuits is closed until the plunger is depressed.

Red brake warning lamp

DESCRIPTION

A red warning lamp is used for the service brake portion of the hydraulic system. The lamp is located in the instrument cluster.

OPERATION

The red warning light alerts the driver if a pressure differential exists between the front and rear hydraulic systems or the parking brakes are applied.

The lamp is turned on momentarily when the ignition switch is turn to the on position. This is a self test to verify the lamp is operational.

Power brake booster

DESCRIPTION

All models use a tandem diaphragm, power brake booster

NOTE: The power brake booster is not a repairable component. The booster must be replaced as an assembly if diagnosis indicates a malfunction has occurred.

OPERATION

The booster unit consists of a single housing divided into two by a tandem diaphragm. The outer edge of the diaphragm is secured to the housing. The booster push rod, which connects the booster to the brake pedal and master cylinder, is attached to the center of the diaphragm. A check valve is used in the booster outlet connected to the engine intake manifold.

Power assist is generated by utilizing a combination of vacuum and atmospheric pressure to boost brake assist.

Master cylinder

DESCRIPTION

A two-piece master cylinder is used on all models.

The cylinder body containing the primary and secondary pistons is made of aluminum. The removable fluid reservoir is made of nylon reinforced with glass fiber. The reservoir stores reserve brake fluid for the hydraulic brake circuits. The reservoir is the only serviceable component.

The fluid compartments of the nylon reservoir are interconnected to permit fluid level equalization.

However, the equalization feature does not affect circuit separation in the event of a front or rear brake malfunction. The reservoir compartments will retain enough fluid to operate the functioning hydraulic circuit.

Care must be exercised when removing/installing the master cylinder connecting lines. The threads in the cylinder fluid ports can be damaged if care is not exercised. Start all brake line fittings by hand to avoid cross threading.

The cylinder reservoir can be replaced when necessary.

However, the aluminum body section of the master cylinder is not a repairable component.

NOTE: If diagnosis indicates that an internal malfunction has occurred, the aluminum body section must be replaced as an assembly.

OPERATION

The master cylinder bore contains a primary and secondary piston. The primary piston supplies hydraulic pressure to the front brakes. The secondary piston supplies hydraulic pressure to the rear brakes.

Combination valve

The combination valve contains a pressure differential valve and switch and a proportioning valve.

The combination valve/proportioning valve are not repairable and must be replaced as an assembly.

PRESSURE DIFFERENTIAL SWITCH

The pressure differential switch is connected to the brake warning lamp. The switch is triggered by movement of the switch valve. The purpose of the switch is to monitor fluid pressure in the separate front/rear brake hydraulic circuits.

A decrease or loss of fluid pressure in either hydraulic circuit will cause the switch valve to shuttle forward or rearward in response to the pressure differential. Movement of the switch valve will push the switch plunger upward. This closes the switch internal contacts completing the electrical circuit to the warning lamp. The switch valve may remain in an actuated position until repair restores system pressures to normal levels.

PROPORTIONING VALVE

The proportioning valve is used to balance frontrear brake action at high decelerations. The valve allows normal fluid pressure during moderate braking.

The valve only controls fluid pressure during high decelerations brake stops, when a percentage of rear weight is transferred to the front wheels.

Front disc brakes

DESCRIPTION

The calipers are a single piston type. The calipers are free to slide laterally, this allows continuous compensation for lining wear.

OPERATION

When the brakes are applied fluid pressure is exerted against the caliper piston. The fluid pressure is exerted equally and in all directions. This means pressure exerted against the caliper piston and within the caliper bore will be equal (Fig. 1).

Fig. 1 Brake Caliper Operation

1 - CALIPER

2 - PISTON

3 - PISTON BORE

4 - SEAL

5 - INBOARD SHOE

6 - OUTBOARD SHOE

Fluid pressure applied to the piston is transmitted directly to the inboard brake shoe. This forces the shoe lining against the inner surface of the disc brake rotor. At the same time, fluid pressure within the piston bore forces the caliper to slide inward on the mounting bolts. This action brings the outboard brake shoe lining into contact with the outer surface of the disc brake rotor.

In summary, fluid pressure acting simultaneously on both piston and caliper, produces a strong clamping action. When sufficient force is applied, friction will attempt to stop the rotors from turning and bring the vehicle to a stop.

Application and release of the brake pedal generates only a very slight movement of the caliper and piston. Upon release of the pedal, the caliper and piston return to a rest position. The brake shoes do not retract an appreciable distance from the rotor. In fact, clearance is usually at, or close to zero. The reasons for this are to keep road debris from getting between the rotor and lining and in wiping the rotor surface clear each revolution.

The caliper piston seal controls the amount of piston extension needed to compensate for normal lining wear.

During brake application, the seal is deflected outward by fluid pressure and piston movement (Fig. 2).

When the brakes (and fluid pressure) are released, the seal relaxes and retracts the piston.

The amount of piston retraction is determined by the amount of seal deflection. Generally the amount is just enough to maintain contact between the piston and inboard brake shoe.

Fig. 2 Lining Wear Compensation By Piston Seal

1 - PISTON

2 - CYLINDER BORE

3 - PISTON SEAL BRAKE PRESSURE OFF

4 - CALIPER HOUSING

5 - DUST BOOT

6 - PISTON SEAL BRAKE PRESSURE ON

Drum brakes

DESCRIPTION

Drum brakes on all models are dual shoe, internal expanding units with an automatic self adjusting mechanism (Fig. 3). Nine inch and eleven inch brakes are used.

OPERATION

When the brake pedal is depressed hydraulic pressure pushes the rear wheel cylinder pistons outward.

The wheel cylinder push rods then push the brake shoes outward against the brake drum. When the brake pedal is released return springs attached to the brake shoes pull the shoes back to there original position.

Fig. 3 Brake Assembly

1 - SUPPORT PLATE

2 - RETURN SPRING

3 - ANCHOR PLATE

4 - RETURN SPRING

5 - CABLE GUIDE

6 - PARKING BRAKE LEVER

7 - ADJUSTER CABLE AND SPRING

8 - SHOE RETAINER, SPRING AND PIN

9 - SECONDARY SHOE AND LINING

10 - LEVER SPRING

11 - ADJUSTER LEVER

12 - ADJUSTER SCREW ASSEMBLY

13 - SHOE SPRING

14 - PRIMARY SHOE AND LINING

15 - PARKING BRAKE STRUT AND SPRING

Parking brakes

DESCRIPTION

The rear drum brake shoes serve as the parking brakes. The parking brakes are operated by a system of cables and levers attached to the rear brake secondary shoes.

OPERATION

The shoes make contact with the brake drum surface by a cable and lever mechanism attached to the secondary brake shoe. The front parking brake cable is connected to the parking brake pedal and to the rear cables. An intermediate cable is used on some vehicles to connect the front and rear cables.

The parking brake pedal assembly is mounted on the driver side cowl panel. The front cable is directly attached to the assembly. The pedal assembly contains a spring loaded mechanism to hold the pedal in the applied position. A rod and spring are used to release the ratchet mechanism and return the pedal to normal position.

Brake hoses and lines

DESCRIPTION

Flexible rubber hose is used at both front brakes and at the rear axle junction block. Double walled steel tubing is used to connect the master cylinder to the major hydraulic braking components and then to the flexible rubber hoses. Double inverted style and ISO style flares are used on the brake lines.

OPERATION

The hoses and lines transmit the brake fluid hydraulic pressure to the calipers and or wheel cylinders.