Файл: 92FWD_5.pdf

GENERAL INFORMATION

The piston boots are of the push-on type and prevent moisture from entering the wheel cylinder.

To perform service operations or inspections of the rear wheel brake cylinders. It will be necessary to remove the cylinders from the support plate and disassemble on the bench.

CAUTION: Wheel cylinders with cup expanders must have cup expanders after any service procedures (reconditioning or replacement).

SERVICE PROCEDURES

REMOVING WHEEL CYLINDERS FROM BRAKE SUPPORT PLATES

With brake drums removed, inspect the wheel cylinder boots for evidence of a brake fluid leak. Then block the brake pedal in the stroke position, and visually check the boots for cuts, tears, or heat cracks. If any of these conditions exist, the wheel cylinders should be completely cleaned, inspected and new parts installed. (A slight amount of fluid on the boot may not be a leak, but maybe preservative fluid used at assembly.)

(1)In case of a leak, remove brake shoes, (replace if soaked with grease or brake fluid.)

(2)Disconnect brake tube from wheel cylinder (Fig.

1).

(3)Remove the rear wheel cylinder attaching bolts (Fig. 1). Then pull wheel cylinder assembly off the brake support plate (Fig. 2).

DISASSEMBLING WHEEL CYLINDERS

To disassemble the wheel cylinders, (Fig. 3) proceed as follows:

(1)Pry boots away from cylinders and remove.

(2)Press IN on one piston to force out opposite piston, cup and spring (with cup expanders). Then using a soft tool such as a dowel rod, press out the cup and piston that remain in the wheel cylinder.

(3)Wash wheel cylinder, pistons, and spring in clean brake fluid or alcohol; (DO NOT USE ANY PETROLEUM BASE SOLVENTS) clean thoroughly and blow dry with compressed air. Inspect cylinder bore and piston for scoring and pitting. (Do not use a rag as lint from the rag will stick to bore surfaces.)

Fig. 1 Brake Tube Disconnected

Fig. 2 Remove or Install Wheel Cylinder

Wheel cylinder bores and pistons that are badly scored or pitted should be replaced. Cylinder walls that have light scratches, or show signs of corrosion, can usually be cleaned with crocus cloth, using a circular motion. Black stains on the cylinder walls are caused by piston cups and will not impair operation of cylinder.

ASSEMBLING WHEEL CYLINDERS

Before assembling the pistons and new cups in the wheel cylinders, dip them in clean brake fluid. If the boots are deteriorated, cracked or do not fit tightly on the pistons or the cylinder casting, install new boots.

(1)Coat cylinder bore with clean brake fluid.

(2)Install expansion spring with cup expanders in cylinder. Install cups in each end of cylinder with open end of cups facing each other (Fig. 3).

(3)Install piston in each end of cylinder having the flat face of each piston contacting the flat face of each cup, already installed (Fig. 3).

(4)Install a boot over each end of cylinder. Be careful not to damage boot during installation.

INSTALLING WHEEL CYLINDERS

(1)Apply Mopart Gasket In-A-Tube or equivalent sealant around wheel cylinder mounting surface (Fig. 4).

(2)Install wheel cylinder onto brake support, and

tighten the wheel cylinder to brake support plate attaching bolts to 8 NIm (75 in. lbs.).

Fig. 4 Apply Sealant on Support Plate

(3)Attach hydraulic brake tube to wheel cylinder, and tighten tube to wheel cylinder fitting to 17 NIm (145 in. lbs.).

(4)Install brake shoes on support plate.

(5)Install rear brake drum onto rear hub. Install

rear wheel and tire assembly, tighten wheel stud nuts to 129 NIm (95 ft. lbs.).

(6)Adjust the rear brakes, (See Adjusting Service Brakes) in Service Adjustments section in this group of the service manual.

(7)Bleed the entire brake system. See (Bleeding Brake System) in Service Adjustments section in this group of the service manual.

Fig. 1 Removing Adjuster Lever Spring

Using a suitable tool such as an aircraft type hose clamp, install the clamp over the retainer on the end of the parking brake cable (Fig. 2). Compress cable housing retainer and start housing out of support plate (Fig. 2). Remove clamp when retainer is free from the park brake cable mounting hole in the rear brake support plate. Alternate method is to slide a 14 mm box wrench over housing end fitting compressing the three fingers.

Fig. 2 Removing Park Brake Cable From Support

Plate

Remove attaching bolts and washers and separate brake support and spindle from rear support trailing arm.

INSTALLATION

Insert parking brake cable and housing into support plate.

Install support plate, spindle and gasket between support plate and spindle on to rear suspension member. Tighten support plate attaching bolts to 71 NIm (53 ft. lbs.) torque.

Attach cable to parking brake lever.

Connect brake tube to wheel cylinder. Tighten brake tube to wheel cylinder fitting to 17 NIm (145 in. lbs.).

Install brake drum and wheel. Adjust and bleed service brakes. Adjust parking brake.

GENERAL INFORMATION

Most models not equipped with an Anti-Lock braking system have a combination hydraulic system control valve in the brake hydraulic system (Fig. 1). The valve is attached to the frame rail below the master cylinder.

rear are part of another. Both systems are routed through, but hydraulically separated by a Pressure Differential Switch. The function of the Pressure Differential Switch is to alert the driver of a malfunction in the brake system.

If hydraulic pressure is lost in one system, the warning light switch will activate a red light on the instrument panel, when the brake pedal is depressed. At this point the brakes require service. However, since the brake systems are split diagonally the vehicle will retain 50% of its stopping capability in the event of a failure in either half.

The warning light switch is the latching type. It will automatically center itself after the repair is made and the brake pedal is depressed.

The instrument panel bulb can be checked each time the ignition switch is turned to the start position or the parking brake is set.

NON-ABS PROPORTIONING UNIT OPERATION

The proportioning valve section operates by transmitting full input pressure to the rear brakes up to a certain point. This is called the split point. Beyond this point it reduces the amount of pressure increase to the rear brakes according to a certain ratio.

Fig. 1 Brake Combination Valve And Warning

Switch Location

The control valve assembly combines a warning switch with a dual proportioning valve (Fig. 2).

Proportioning valves balance front to rear braking by controlling at a given ratio, the increase in rear system hydraulic pressure above a preset level. Under light pedal application, the valve allows full hydraulic pressure to the rear brakes.

There is only one valve assembly in each vehicle, see Valve Application Chart. During any service procedures identify valve assemblies by part number as well as split point (PSI) and slope.

PRESSURE DIFFERENTIAL WARNING LIGHT SWITCH

The hydraulic brake system, on non-ABS vehicles, is split diagonally. The left front and right rear brakes are part of one system. And the right front and left

Fig. 2 Switch and Valve Assembly

On light pedal applications equal brake pressure will be transmitted to the front and rear brakes. On