# Brake Operating System

## Basic Operating Principles

Hydraulic systems are used to actuate the brakes of all modern automobiles. The system transports the power required to force the frictional surfaces of the braking system together from the pedal to the individual brake units at each wheel. A hydraulic system is used for two reasons.

First, fluid under pressure can be carried to all parts of an automobile by small pipes and flexible hoses without taking up a significant amount of room or posing routing problems.

Second, a great mechanical advantage can be given to the brake pedal end of the system, and the foot pressure required to actuate the brakes can be reduced by making the surface area of the master cylinder pistons smaller than that of any of the pistons in the wheel cylinders or calipers.

The master cylinder consists of a fluid reservoir along with a double cylinder and piston assembly. Double type master cylinders are designed to separate the front and rear braking systems hydraulically in case of a leak. The master cylinder coverts mechanical motion from the pedal into hydraulic pressure within the lines. This pressure is translated back into mechanical motion at the wheels by either the wheel cylinder (drum brakes) or the caliper (disc brakes).

Steel lines carry the brake fluid to a point on the vehicle's frame near each of the vehicle's wheels. The fluid is then carried to the calipers and wheel cylinders by flexible tubes in order to allow for suspension and steering movements.

In drum brake systems, each wheel cylinder contains two pistons, one at either end, which push outward in opposite directions and force the brake shoe into contact with the drum.

In disc brake systems, the cylinders are part of the calipers. At least one cylinder in each caliper is used to force the brake pads against the disc.

All pistons employ some type of seal, usually made of rubber, to minimize fluid leakage. A rubber dust boot seals the outer end of the cylinder against dust and dirt. The boot fits around the outer end of the piston on disc brake calipers, and around the brake actuating rod on wheel cylinders.

The hydraulic system operates as follows: When at rest, the entire system, from the piston(s) in the master cylinder to those in the wheel cylinders or calipers, is full of brake fluid. Upon application of the brake pedal, fluid trapped in front of the master cylinder piston(s) is forced through the lines to the wheel cylinders. Here, it forces the pistons outward, in the case of drum brakes, and inward toward the disc, in the case of disc brakes. The motion of the pistons is opposed by return springs mounted outside the cylinders in drum brakes, and by spring seals, in disc brakes.

Upon release of the brake pedal, a spring located inside the master cylinder immediately returns the master cylinder pistons to the normal position. The pistons contain check valves and the master cylinder has compensating ports drilled in it. These are uncovered as the pistons reach their normal position. The piston check valves allow fluid to flow toward the wheel cylinders or calipers as the pistons withdraw. Then, as the return springs force the brake pads or shoes into the released position, the excess fluid reservoir through the compensating ports. It is during the time the pedal is in the released position that any fluid that has leaked out of the system will be replaced through the compensating ports.

Dual circuit master cylinders employ two pistons, located one behind the other, in the same cylinder. The primary piston is actuated directly by mechanical linkage from the brake pedal through the power booster. The secondary piston is actuated by fluid trapped between the two pistons. If a leak develops in front of the secondary piston, it moves forward until it bottoms against the front of the master cylinder, and the fluid trapped between the pistons will operate the rear brakes. If the rear brakes develop a leak, the primary piston will move forward until direct contact with the secondary piston takes place, and it will force the secondary piston to actuate the front brakes. In either case, the brake pedal moves farther when the brakes are applied, and less braking power is available.

All dual circuit systems use a switch to warn the driver when only half of the brake system is operational. This switch is usually located in a valve body which is mounted on the firewall or the frame below the master cylinder. A hydraulic piston receives pressure from both circuits, each circuit's pressure being applied to one end of the piston. When the pressures are in balance, the piston remains stationary. When one circuit has a leak, however, the greater pressure in that circuit during application of the brakes will push the piston to one side, closing the switch and activating the brake warning light.

In disc brake systems, this valve body also contains a metering valve and, in some cases, a proportioning valve. The metering valve keeps pressure from traveling to the disc brakes on the front wheels until the brake shoes on the rear wheels have contacted the drums, ensuring that the front brakes will never be used alone. The proportioning valve controls the pressure to the rear brakes to lessen the chance of rear wheel lock-up during very hard braking.

Warning lights may be tested by depressing the brake pedal and holding it while opening one of the wheel cylinder bleeder screws. If this does not cause the light to go on, substitute a new lamp, make continuity checks, and, finally, replace the switch as necessary.

The hydraulic system may be checked for leaks by applying pressure to the pedal gradually and steadily. If the pedal sinks very slowly to the floor, the system has a leak. This is not to be confused with a springy or spongy feel due to the compression of air within the lines. If the system leaks, there will be a gradual change in the position of the pedal with a constant pressure.

Check for leaks along all lines and at wheel cylinders. If no external leaks are apparent, the problem is inside the master cylinder.

### DISC BRAKES

Instead of the traditional expanding brakes that press outward against a circular drum, disc brake systems utilize a disc (rotor) with brake pads positioned on either side of it. An easily-seen analogy is the hand brake arrangement on a bicycle. The pads squeeze onto the rim of the bike wheel, slowing its motion. Automobile disc brakes use the identical principle but apply the braking effort to a separate disc instead of the wheel.

The disc (rotor) is a casting, usually equipped with cooling fins between the two braking surfaces. This enables air to circulate between the braking surfaces making them less sensitive to heat buildup and more resistant to fade. Dirt and water do not drastically affect braking action since contaminants are thrown off by the centrifugal action of the rotor or scraped off the by the pads. Also, the equal clamping action of the two brake pads tends to ensure uniform, straight line stops. Disc brakes are inherently self-adjusting. There are three general types of disc brake:

- A fixed caliper.
- A floating caliper.
- A sliding caliper.

The fixed caliper design uses two pistons mounted on either side of the rotor (in each side of the caliper). The caliper is mounted rigidly and does not move.

The sliding and floating designs are quite similar. In fact, these two types are often lumped together. In both designs, the pad on the inside of the rotor is moved into contact with the rotor by hydraulic force. The caliper, which is not held in a fixed position, moves slightly, bringing the outside pad into contact with the rotor. There are various methods of attaching floating calipers. Some pivot at the bottom or top, and some slide on mounting bolts. In any event, the end result is the same.

### DRUM BRAKES

Drum brakes employ two brake shoes mounted on a stationary backing plate. These shoes are positioned inside a circular drum which rotates with the wheel assembly. The shoes are held in place by springs. This allows them to slide toward the drums (when they are applied) while keeping the linings and drums in alignment. The shoes are actuated by a wheel cylinder which is mounted at the top of the backing plate. When the brakes are applied, hydraulic pressure forces the wheel cylinder's actuating links outward. Since these links bear directly against the top of the brake shoes, the tops of the shoes are then forced against the inner side of the drum. This action forces the bottoms of the two shoes to contact the brake drum by rotating the entire assembly slightly (known as servo action). When pressure within the wheel cylinder is relaxed, return springs pull the shoes back away from the drum.

Most modern drum brakes are designed to self-adjust themselves during application when the vehicle is moving in reverse. This motion causes both shoes to rotate very slightly with the drum, rocking an adjusting lever, thereby causing rotation of the adjusting screw. Some drum brake systems are designed to self-adjust during application whenever the brakes are applied. This on-board adjustment system reduces the need for maintenance adjustments and keeps both the brake function and pedal feel satisfactory.

### POWER BOOSTERS

Virtually all modern vehicles use a vacuum assisted power brake system to multiply the braking force and reduce pedal effort. Since vacuum is always available when the engine is operating, the system is simple and efficient. A vacuum diaphragm is located on the front of the master cylinder and assists the driver in applying the brakes, reducing both the effort and travel he must put into moving the brake pedal.

The vacuum diaphragm housing is normally connected to the intake manifold by a vacuum hose. A check valve is placed at the point where the hose enters the diaphragm housing, so that during periods of low manifold vacuum brakes assist will not be lost.

Depressing the brake pedal closes off the vacuum source and allows atmospheric pressure to enter on one side of the diaphragm. This causes the master cylinder pistons to move and apply the brakes. When the brake pedal is released, vacuum is applied to both sides of the diaphragm and springs return the diaphragm and master cylinder pistons to the released position.

If the vacuum supply fails, the brake pedal rod will contact the end of the master cylinder actuator rod and the system will apply the brakes without any power assistance. The driver will notice that much higher pedal effort is needed to stop the car and that the pedal feels harder than usual.

#### Vacuum Leak Test

1. Operate the engine at idle without touching the brake pedal for at least one minute.
2. Turn off the engine and wait one minute.
3. Test for the presence of assist vacuum by depressing the brake pedal and releasing it several times. If vacuum is present in the system, light application will produce less and less pedal travel. If there is no vacuum, air is leaking into the system.

#### System Operation Test

1. With the engine OFF, pump the brake pedal until the supply vacuum is entirely gone.
2. Put light, steady pressure on the brake pedal.
3. Start the engine and let it idle. If the system is operating correctly, the brake pedal should fall toward the floor if the constant pressure is maintained.

Power brake systems may be tested for hydraulic leaks just as ordinary systems are tested.

WARNING
Clean, high quality brake fluid is essential to the safe and proper operation of the brake system. You should always buy the highest quality brake fluid that is available. If the brake fluid becomes contaminated, drain and flush the system, then refill the master cylinder with new fluid. Never reuse any brake fluid. Any brake fluid that is removed from the system should be discarded.

## Brake Light Switch

### REMOVAL & INSTALLATION

#### 1997-98 F-250HD, F-350 and F-Super Duty

Exploded view of the brake light switch

Click to enlarge

1. Lift the locking tab on the switch connector and disconnect the wiring.
2. Remove the hairpin retainer, slide the stop lamp switch, pushrod and nylon washer off of the pedal. Remove the washer, then the switch by sliding it up or down.

On trucks equipped with speed control, the spacer washer is replaced by the dump valve adapter washer.

3. To install the switch, position it so that the U-shaped side is nearest the pedal and directly over/under the pin.
4. Slide the switch up or down, trapping the master cylinder pushrod and bushing between the switch side plates.
5. Push the switch and pushrod assembly firmly towards the brake pedal arm. Assemble the outside white plastic washer to the pin and install the hairpin retainer.

CAUTION
Don't substitute any other type of retainer. Use only the Ford specified hairpin retainer.

6. Assemble the connector on the switch.
7. Check stop lamp operation.

CAUTION
Make sure that the stop lamp switch wiring has sufficient travel during a full pedal stroke!

#### F-150, F-250, Expedition and Navigator; 1999-00 F-250SD, F-350, and F-Super Duty Models

Brake pedal position switch removal— F-150, F-250, Expedition and Navigator; 1999-00 F-250SD, F-350, and F-Super Duty Models

1. Disconnect the negative battery cable.
2. Disconnect the brake pedal position switch.
3. Remove the self-locking pin.
4. Remove the brake pedal position switch from the brake master cylinder push rod.
5. Remove the brake master cylinder push rod spacer.
6. Remove the brake master cylinder push rod bushing.
7. The installation is the reverse of the removal.

## Master Cylinder

### REMOVAL & INSTALLATION

#### 1997-98 F-250HD, F-350 and F-SuperDuty

Master cylinder mounting—1997-98 F-250HD, F-350 and F-SuperDuty

Click to enlarge

1. With the engine OFF, depress the brake pedal several times to expel any vacuum.
2. Disconnect the fluid level warning switch wire.
3. Disconnect the hydraulic system brake lines at the master cylinder.
4. Remove the master cylinder retaining nuts and remove the master cylinder.

To install:

5. Position the master cylinder assembly on the booster and install the retaining nuts. Tighten the nuts to 18-25 ft. lbs. (25-34 Nm).
6. Connect the hydraulic brake system lines to the master cylinder.
7. Connect the wiring.
8. Bleed the master cylinder.

#### F-150, F-250, Expedition and Navigator

Detach the fluid level electrical harness connector

Click to enlarge

If equipped with speed control, detach the brake pressure switch electrical harness connector

Click to enlarge

Use a suitable size flare nut wrench to ...

... loosen the brake line fittings at the master cylinder

Plug the brake lines and inlet ports of the master cylinder

Remove the 2 retaining nuts and position the RABS valve out of the way

Remove the 2 retaining nuts and ...

... remove the master cylinder from the brake booster

1. Disconnect the negative battery cable.
2. Detach the fluid level electrical harness connector from the master cylinder reservoir.
3. If equipped with speed control, detach the brake pressure switch electrical harness connector.
4. Disconnect and plug 2 brake lines at the brake master cylinder ports.
5. If the vehicle is equipped with rear anti-lock brakes, remove 2 retaining nuts and position the RABS valve out of the way using care not to damage the brake lines.
6. Remove the 2 brake master cylinder retaining nuts and remove the master cylinder.

To install:

7. Bench bleed the brake master cylinder before installation.
8. Place the brake master cylinder to the power brake booster. Install 2 retaining nuts and tighten to 21 ft. lbs. (29 Nm).
9. If equipped, install the RABS valve and 2 retaining nuts. Tighten to 15-21 ft. lbs. (21-29 Nm).
10. Unplug and connect 2 brake lines to the brake master cylinder ports and tighten the fittings to 11-15 ft. lbs. (15-20 Nm).
11. If equipped, connect the brake pressure switch electrical harness connector.
12. Connect the electrical harness connector to the low fluid level warning switch.
13. Fill the brake master cylinder with clean DOT 3 or equivalent brake fluid from a closed container.
14. Bleed the entire brake system following the proper procedure.
15. Road test the vehicle and check for proper brake system operation.

#### 1999-00 F-250SD, F-350 and F-Super Duty

##### EXCEPT HYDRO-MAX

1. Disconnect the negative battery cable.
2. Remove the air cleaner housing.
3. Detach the fluid level sensor connector.
4. Detach the brake pressure switch connector, if so equipped.
5. Disconnect the brake tubes.
6. Remove the bolts retaining the power steering tubes to the bracket.
7. Remove the brake master cylinder nuts.
8. Remove the power steering tube retaining bracket.
9. Remove the brake master cylinder.

To install:

10. The installation is the reverse of the removal.

##### WITH HYDRO-MAX

WARNING
Do not depress the brake pedal while the hydraulic fluid supply line is disconnected. The inlet pressure port check ball may be dislodged which will result in a non-functional backup system.

1. Disconnect the negative battery cable.
2. Remove the support bracket bolt and nut.
3. Disconnect the brake tubes.
4. Remove the ground wire nut and the ground wire.
5. Remove the four master cylinder retaining nuts.
6. Remove the master cylinder.

To install:

7. The installation is the reverse of the removal.

### BENCH BLEEDING

WARNING
All new master cylinders should be bench bled prior to installation. Bleeding a new master cylinder on the vehicle is not a good idea. With air trapped inside, the master cylinder piston may bottom in the bore and possibly cause internal damage.

1. Secure the master cylinder in a bench vise using soft jaws.
2. Remove the master cylinder reservoir cap.
3. Manufacture or purchase bleeding tubes and install them on the master cylinder as illustrated.
4. Fill the master cylinder reservoir with clean, fresh brake fluid until the level is within 0.25 in. of the reservoir top.

Ensure the bleeding tubes are below the level of the brake fluid, otherwise air may get into the system making your bleeding efforts ineffective.

5. Use a blunt tipped rod (a long socket extension works well) to slowly depress the master cylinder piston. Make sure the piston travels full its full stroke.
6. As the piston is depressed, bubbles will come out of the bleeding tubes. Continue depressing and releasing the piston until all bubbles cease.
7. Refill the master cylinder with fluid.
8. Remove the bleeding tubes.
9. Install the master cylinder reservoir cap.
10. Install the master cylinder on the vehicle.

## Power Brake Booster

### REMOVAL & INSTALLATION

#### F-150, F-250, Expedition and Navigator

Brake booster assembly— F-150, F-250, Expedition and Navigator; 1999-00 F-Super Duty models with vacuum assisted booster

Click to enlarge

1. Remove the master cylinder.
2. Disconnect the power brake booster hose.
3. Remove the stoplight switch self-locking pin.
4. Slide the stoplight switch and booster push rod off the brake pedal pin.
5. Remove the bulkhead sound insulator.
6. Remove the power brake booster nuts and remove the booster.

To install:

7. The installation is the reverse of the removal.

#### 1997-98 F-250HD, F-350 and F-Super Duty

##### WITH HYDROBOOST BRAKES

Hydro-Boost system on the F-Super Duty chassis cab

Click to enlarge

Hydro-Boost system on the F-Super Duty commercial stripped chassis

Click to enlarge

Hydro-Boost system on the F-Super Duty motor home chassis

Click to enlarge

CAUTION
Do not depress the brake pedal with the master cylinder removed!

1. Depress the brake pedal several times with the engine off to exhaust the pressure in the accumulator.
2. Remove the master cylinder from the Hydro-Boost unit. Do not disconnect the brake lines from the master cylinder! Position the master cylinder out of the way.
3. Disconnect the 3 hydraulic lines from the Hydro-Boost unit.
4. Disconnect the pushrod from the brake pedal.
5. Remove the booster mounting nuts and lift the booster from the firewall.

CAUTION
The booster should never be carried by the accumulator. The accumulator contains high pressure nitrogen and can be dangerous if mishandled! If the accumulator is to be disposed of, do not expose it to fire or other forms of incineration! Gas pressure can be relieved by drilling a 1/16 in. (1.5mm) hole in the end of the accumulator can. Always wear safety goggles during the drilling!

6. Installation is the reverse of removal. Tighten the booster mounting nuts to 25 ft. lbs. (34 Nm); the master cylinder nuts to 25 ft. lbs. (34 Nm); connect the hydraulic lines, refill and bleed the booster as follows:
   1. Fill the pump reservoir with Dexron®II ATF.
   2. Disconnect the coil wires and crank the engine for several seconds.
   3. Check the fluid level and refill, if necessary.
   4. Connect the coil wires and start the engine.
   5. With the engine running, turn the steering wheel lock-to-lock twice. Shut off the engine.
   6. Depress the brake pedal several times to discharge the accumulator.
   7. Start the engine and repeat Step 6e.
   8. If foam appears in the reservoir, allow the foam to dissipate.
   9. Repeat Step 6e as often as necessary to expel all air from the system.

The system is, in effect, self-bleeding and normal vehicle operation will expel any further trapped

##### WITH VACUUM ASSISTED BOOSTER

Brake booster assembly—1997-98 F-250HD, F-350 and F-Super Duty wit vacuum assist

Click to enlarge

1. Disconnect the brake light switch wires.
2. Support the master cylinder from below, with a prop of some kind.
3. Loosen the clamp and remove the booster check valve hose.
4. Remove the wraparound clip from the booster inboard stud.
5. Remove the master cylinder from the booster. Keep it supported. It will not be necessary to disconnect the brake lines.
6. Working inside the truck below the instrument panel, disconnect the booster valve operating rod from the brake pedal assembly.
7. Remove the 4 bracket-to-dash panel attaching nuts.
8. Remove the booster and bracket assembly from the dash panel, sliding the valve operating rod out from the engine side of the dash panel.

To install:

9. Mount the booster and bracket assembly on the dash panel by sliding the valve operating rod in through the hole in the dash panel, and installing the attaching nuts. Tighten the nuts to 18-25 ft. lbs. (24-34 Nm).
10. Connect the manifold vacuum hose to the booster.
11. Install the master cylinder. Tighten the nuts to 18-25 ft. lbs. (24-34 Nm).
12. Install the wraparound clip.
13. Connect the stop light switch wires.
14. Working inside the truck below the instrument panel, connect the pushrod and stoplight switch.

#### 1999-00 F-250SD, F-350 and F-Super Duty

##### WITH HYDRO-BOOST BRAKES

Hydro-boost brake booster assembly

WARNING
The power brake booster should not be carried by the accumulator, nor should it ever be dropped on the accumulator. Check the snap ring on the accumulator for proper seating before the power brake booster is used. The accumulator contains high-pressure nitrogen gas and can be dangerous if mishandled.

1. With the engine off, depress the brake pedal several times to discharge the accumulator.
2. Disconnect the negative battery cable.
3. Remove the left side battery.
4. Remove the air cleaner housing.
5. Remove the brake pressure switch electrical connector.
6. Disconnect the power steering pressure hoses.
7. Disconnect the power steering return line hose.
8. Remove the three power steering line clamp bolts.
9. Remove the brake master cylinder nuts.
10. Remove the power steering hose mounting bracket and the brake master cylinder, and position aside.
11. Remove the fuse panel cover.
12. Remove the stoplight switch self-locking pin.
13. Remove the stoplight switch and the brake booster push rod from the brake pedal pin.
14. Remove the power brake booster nuts, and remove the power brake booster.

To install:

CAUTION
If the accumulator is to be disposed of, it must not be exposed to excessive heat. Before discarding the accumulator, drill a 1/16 inch (1.6-mm) diameter hole in the end of the accumulator can to relieve the gas pressure. Always wear safety glasses when performing this operation.

15. The installation is the reverse of the removal.
16. Install new Teflon® seals on the power steering pressure fittings.

##### WITH VACUUM ASSISTED BOOSTER

Brake booster assembly— F-150, F-250, Expedition and Navigator; 1999-00 F-Super Duty models with vacuum assisted booster

1. Disconnect the negative battery cable.
2. Remove the air cleaner housing.
3. Remove the brake master cylinder nuts.
4. Position the brake master cylinder aside.
5. Disconnect the booster vacuum hose.
6. Disconnect the power distribution box auxiliary relay and set aside.
7. Remove the fuse panel cover.
8. Remove the stoplight switch self-locking pin.
9. Remove the stoplight switch and the brake booster push rod from the brake pedal pin.
10. Remove the power brake booster nuts.
11. Remove the power brake booster.

To install:

12. The installation is the reverse of the removal.

##### WITH HYDRO-MAX BRAKES

Hydro-max brake booster assembly

1. Disconnect the negative battery cable.
2. Remove the support bracket bolt and nut.
3. Remove the ground wire nut and the ground wire.
4. Remove the four master cylinder nuts.
5. Position the master cylinder aside.
6. Remove the electric motor relay bolt.
7. Detach the flow switch electrical connector.
8. Remove the steering column cover.
9. Remove the stoplight switch self-locking pin.
10. Remove the stoplight switch and the brake booster push rod from the brake pedal.
11. Detach the electric pump and motor assembly electric connector.
12. Disconnect the hydraulic fluid return hose.
13. Remove the hydraulic fluid supply line nut.
14. Remove the Hydro-Max booster nuts, and remove the Hydro-Max booster.
15. The installation is the reverse of the removal.

Start the hydraulic fluid supply line before tightening the Hydro-Max nuts and bolts.

## Diesel Engine Vacuum Pump

### REMOVAL & INSTALLATION

Vacuum pump mounting—7.3L diesel engine

Click to enlarge

1. Disconnect the negative battery cable.
2. Drain and recycle the engine coolant.
3. Remove the drive belt.
4. Remove the upper radiator hose clamps and upper radiator hose.
5. Disconnect the coolant reservoir hose at the radiator.
6. Remove the fan shroud, fan blade and fan clutch. Refer to Section 3.
7. Remove the vacuum pump pulley using pulley remover T69L-10300-B or equivalent.
8. Remove the vacuum pump retaining bolts.
9. Disconnect the vacuum pump hose and remove the vacuum pump.

To install:

10. The installation is the reverse of the removal.
11. Fill the engine with the proper mixture of coolant and water. Bleed the system.

## Proportioning Valve

### REMOVAL & INSTALLATION

#### 1997-98 F-Super Duty Only

Setting the correct indexing height for the height sensing proportioning valve

Click to enlarge

A common height sensing proportioning valve—F-Super Duty models

Click to enlarge

If the linkage is disconnected from the valve, the proper setting of the valve will be lost and a new valve will have to be installed. The new valve will have the shaft preset and secured internally. If the shaft of the new valve turns freely, DO NOT USE IT!—The valve cannot be repaired or disassembled. It is to be replaced as a unit.—If the linkage is damaged or broken and requires replacement, a new sensing valve will also be required.

1. Raise and support the rear end on jackstands.
2. Raise the frame to obtain a clearance of 6 5/8 in. (168.3mm) between the bottom edge of the rubber jounce bumper and the top of the axle tube—on BOTH sides of the axle. The is the correct indexing height for the valve.
3. Remove the nut holding the linkage arm to the valve and disconnect the arm.
4. Remove the bolt holding the flexible brake hose to the valve.
5. Disconnect the brake line from the valve.
6. Remove the 2 mounting bolts and remove the valve from its bracket.

To install:

7. Place the new valve on the bracket and tighten the mounting bolts to 12-18 ft. lbs. (16-24 Nm).
8. Install the brake hose, using new copper gaskets and tighten the bolt to 28-34 ft. lbs. (38-46 Nm).
9. Attach the brake line to the lower part of the valve.
10. Connect the linkage arm to the valve and tighten the nut to 8-10 ft. lbs. (11-13 Nm).
11. Bleed the brakes.

When servicing axle or suspension parts which would require disconnection of the valve, instead, remove the 2 nuts that attach the linkage arm to the axle cover plate. This will avoid disconnecting the valve and avoid having to replace the valve.

## Brake Hoses and Lines

Metal lines and rubber brake hoses should be checked frequently for leaks and external damage. Metal lines are particularly prone to crushing and kinking under the vehicle. Any such deformation can restrict the proper flow of fluid and therefore impair braking at the wheels. Rubber hoses should be checked for cracking or scraping; such damage can create a weak spot in the hose and it could fail under pressure.

Any time the lines are removed or disconnected, extreme cleanliness must be observed. Clean all joints and connections before disassembly (use a stiff bristle brush and clean brake fluid); be sure to plug the lines and ports as soon as they are opened. New lines and hoses should be flushed clean with brake fluid before installation to remove any contamination.

### REMOVAL & INSTALLATION

1. Disconnect the negative battery cable.
2. Raise and safely support the vehicle on jackstands.
3. Remove any wheel and tire assemblies necessary for access to the particular line you are removing.
4. Thoroughly clean the surrounding area at the joints to be disconnected.

Use a brush to clean the fittings of any debris

5. Place a suitable catch pan under the joint to be disconnected.
6. Using two wrenches (one to hold the joint and one to turn the fitting), disconnect the hose or line to be replaced.

Use two wrenches to loosen the fitting. If available, use flare nut type wrenches

7. Disconnect the other end of the line or hose, moving the drain pan if necessary. Always use a back-up wrench to avoid damaging the fitting.
8. Disconnect any retaining clips or brackets holding the line and remove the line from the vehicle.

If the brake system is to remain open for more time than it takes to swap lines, tape or plug each remaining clip and port to keep contaminants out and fluid in.

Any gaskets/crush washers should be replaced with new ones during installation

Tape or plug the line to prevent contamination

To install:

9. Install the new line or hose, starting with the end farthest from the master cylinder. Connect the other end, then confirm that both fittings are correctly threaded and turn smoothly using finger pressure. Make sure the new line will not rub against any other part. Brake lines must be at least 1/2 in. (13mm) from the steering column and other moving parts. Any protective shielding or insulators must be reinstalled in the original location.

WARNING
Make sure the hose is NOT kinked or touching any part of the frame or suspension after installation. These conditions may cause the hose to fail prematurely.

10. Using two wrenches as before, tighten each fitting.
11. Install any retaining clips or brackets on the lines.
12. If removed, install the wheel and tire assemblies, then carefully lower the vehicle to the ground.
13. Refill the brake master cylinder reservoir with clean, fresh brake fluid, meeting DOT 3 specifications. Properly bleed the brake system.
14. Connect the negative battery cable.

## Bleeding Brake System

Bleeder valve location—drum brakes

Click to enlarge

Place a wrench onto the bleeder valve, connect a hose and carefully open the bleeder valve to bleed the brakes—drum brakes

Place a wrench onto the bleeder valve, connect a hose and carefully open the bleeder valve to bleed the brakes—disc brakes

Click to enlarge

When any part of the hydraulic system has been disconnected for repair or replacement, air may get into the lines and cause spongy pedal action (because air can be compressed and brake fluid cannot). To correct this condition, it is necessary to bleed the hydraulic system so to be sure all air is purged.

When bleeding the brake system, bleed one brake cylinder at a time, beginning at the cylinder with the longest hydraulic line (farthest from the master cylinder) first. ALWAYS Keep the master cylinder reservoir filled with brake fluid during the bleeding operation. Never use brake fluid that has been drained from the hydraulic system, no matter how clean it is.

The primary and secondary hydraulic brake systems are separate and are bled independently. During the bleeding operation, do not allow the reservoir to run dry. Keep the master cylinder reservoir filled with brake fluid.

1. Clean all dirt from around the master cylinder fill cap, remove the cap and fill the master cylinder with brake fluid until the level is within 1/4 in. (6mm) of the top edge of the reservoir.
2. Clean the bleeder screws at all 4 wheels. The bleeder screws are located on the back of the brake backing plate (drum brakes) and on the top of the brake calipers (disc brakes).
3. Attach a length of rubber hose over the bleeder screw and place the other end of the hose in a glass jar, submerged in brake fluid.
4. Open the bleeder screw 1/2-3/4 turn. Have an assistant slowly depress the brake pedal.
5. Close the bleeder screw and tell your assistant to allow the brake pedal to return slowly. Continue this process to purge all air from the system.
6. When bubbles cease to appear at the end of the bleeder hose, close the bleeder screw and remove the hose. Tighten the bleeder screw to the proper torque:

- Check the master cylinder fluid level and add fluid accordingly. Do this after bleeding each wheel.
- Repeat the bleeding operation at the remaining 3 wheels, ending with the one closet to the master cylinder.
- Fill the master cylinder reservoir to the proper level.