Initial Inspection and Diagnostic Overview

Principles of Operation

Hydraulic Brake System
Applying the brake pedal uses lever action to push a rod into the brake booster, which through the use of vacuum, boosts the force of the rod and then transmits this force into the master cylinder. This produces hydraulic pressure in the master cylinder. On vehicles not equipped with anti-lock brake systems (ABS), the hydraulic pressure is transmitted by brake fluid through the brake hoses/tubes to the individual brake calipers or wheel cylinders. On vehicles equipped with ABS, the hydraulic pressure is transmitted by brake fluid through the brake hoses/tubes to the ABS hydraulic control unit (HCU), which then distributes that pressure to the individual brake calipers or wheel cylinders. The brake calipers or wheel cylinders use hydraulic pressure to apply the pads or shoes. The application of the brake pads or shoes will cause the rotation of the wheels to slow or stop depending on how much brake pressure is applied. The parking brakes carry out the same function except that they are mechanically actuated by a cable that connects only to the rear brakes.

Adjustable Pedals
The brake pedal position is changed in phase with the accelerator pedal. The system is adjusted by pressing the dash-mounted switch that powers the adjustable pedal motor mounted on the accelerator pedal assembly. The 2-way motor operates backward (toward the driver) or forward (away from the driver) to adjust the accelerator pedal directly and the brake pedal through the drive cable attached to the brake pedal assembly.

Inspection and Verification

WARNING: If equipped with fire suppression system, refer to Important Safety Warnings.

WARNING: Use of any brake fluid other than the approved DOT 3 will cause permanent damage to brake components and will render the brakes inoperative. Failure to follow these instructions may result in personal injury.

WARNING: Carefully read cautionary information on product label. For EMERGENCY MEDICAL INFORMATION seek medical advice. In the USA or Canada on Ford/Motorcraft products call: 1-800-959-3673. For additional information, consult the product Material Safety Data Sheet (MSDS) if available. Failure to follow these instructions may result in personal injury.

CAUTION: Blistering or swelling of rubber brake components can indicate contamination of the brake fluid by a petroleum-based substance. Contaminated rubber components in the hydraulic brake system must be replaced and the entire hydraulic brake system must be flushed with clean brake fluid to prevent recontamination.

CAUTION: Do not spill brake fluid onto painted or plastic surfaces. If spilled, wipe up immediately before damage to the painted or plastic surface occurs.

NOTE: Always check the fluid level in the brake master cylinder reservoir before carrying out the test procedures. If the fluid level is not at the correct level, clean the reservoir cap before removing, then add clean, specified brake fluid.

NOTE: Prior to carrying out any diagnosis, make sure the red brake warning indicator is functional.


The first indication that something may be wrong in the brake system is a change in the feeling through the brake pedal. The red brake warning indicator in the instrument cluster and the brake fluid level in the brake master cylinder reservoir are also indicators of system concerns.

If a wheel is locked and the vehicle must be moved, open a bleeder screw at the locked wheel to let out enough fluid to relieve the pressure. Close the bleeder screw. This bleeding operation may release the brakes but will not correct the cause of the trouble. If this does not relieve the locked wheel condition, repair the locked components before proceeding.

Inspect all hoses and connections. All unused vacuum connectors should be capped. Make sure hoses and their connections are correctly secured and in good condition with no holes, soft or collapsed areas.

Road Test
The technician should have a thorough knowledge of the brake system operation and accepted general braking guidelines in order to detect any problems.

Select a road that is reasonably smooth and level. Gravel or bumpy roads are not suitable because the surface does not allow the tires to grip the road equally. Avoid crowned roads.

A key factor in evaluating brake concerns is the deceleration rate. This varies from vehicle to vehicle and with changes in operating conditions. It is evident how well the brakes are working after just a few applications.

Brake Pads

NOTE: It is not required to install new brake pads if friction material properties are within guidelines. It is also not required to install new brake pads when the brake discs are machined.
^ Remove the brake pads.
^ Inspect and measure the thickness of the brake pad friction material.
- Install new brake pads if the thickness of the friction material is less than 3.0 mm (0.118 inch).
- Compare all 4 front or rear pads for uneven wear. Install new brake pads if the thickness of the friction material varies from pad to pad by more than 2.0 mm (0.079 inch).
- Install new brake pads if there are missing chunks or cracks in the lining through to the backing plate.
- If the friction material shows taper wear (for example, the thickness varies by more than 3.0 mm [0.118 inch] in any direction) verify the caliper guide pins are functioning correctly.

Brake Discs

CAUTION: Using an impact tool without a torque socket will lead to unevenly tightened lug nuts. This causes brake disc on-vehicle lateral runout and brake roughness.

NOTE: It is generally not required to install new brake discs to address noise issues.

^ Remove the brake disc.
^ Inspect the brake discs and measure the brake disc thickness in a minimum of 4 places around the circumference of the brake disc. Record the measurements.
- Install new brake discs if any thickness measurement is less than the minimum specification.
- Install new brake discs if cracked.
- Machine the brake discs if the diagnosis has revealed vibration in the steering wheel, seat or pedal while braking. Heavily scored brake discs, similar to that caused by pads worn down to the backing plate, should also be machined. In order to machine, discs must be above the minimum thickness to machine specification.

Brake Caliper
Inspect the brake calipers for:
^ brake fluid leaks.
^ boots and seals for tears or cracks.
^ caliper piston for binding and corrosion.
^ guide pins for correct operation.

Brake Caliper Guide Pins

CAUTION: Do not use power tools for caliper guide pin bore cleaning.

The guide pins should slide with a reasonable amount of hand force. If the brake pads show taper wear or the guide pins are difficult to move, then carry out the following steps.

NOTE: If a guide pin kit is not available, install a new caliper assembly.

^ Disassemble the guide pins.
^ Use a wire brush, rolled-up sandpaper or emery cloth to remove all corrosion and foreign material from the caliper guide pin bores. Clean remaining foreign material from the bores with brake parts cleaner and compressed air.
^ Install new brake pads if the lining is not within specifications.
^ Assemble the caliper guide pins using new caliper seals, boots and guide pins. Use an ample amount of grease to lubricate the bores and guide pins.

Brake Hoses and Tubes

CAUTION: Never use copper tubing. It is subject to fatigue, cracking and corrosion, which could result in brake tube failure.

^ Double-wall steel tubing is used throughout the brake hydraulic system. All brake tube fittings must be correctly double flared to provide strong, leakproof connections. When bending tubing to fit the underbody or rear axle contours, be careful not to kink or crack the tube.
^ If a section of the brake tube is damaged, the entire section must be installed new with a tube of the same type, size, shape and length.
^ When installing the hydraulic brake tubing, hoses or connectors, tighten all connections to specifications. After installation, bleed the brake system.
^ The wet appearance on the outer cover of rubber brake hoses is called "sweating." This is a normal condition for neoprene rayon braid hose and is not a sign of leakage or cause to install a new hose.

Install a new flexible brake hose if the hose shows signs of softening, cracking or other damage.

When installing a new brake hose or tube, position the hose or tube to avoid contact with other vehicle components.

Non-Pressure Leaks

NOTE: The wet appearance on the outer cover of rubber brake hoses is called "sweating." This is a normal condition for neoprene rayon braid hose. The sweating condition is not evidence of a brake fluid leak and will not result in a loss of pressure in the system.

The only part of the brake system that could have a brake fluid loss that does not appear when the system is under pressure is the brake master cylinder reservoir under the following conditions:
^ Missing or poorly-fitted brake master cylinder filler cap
^ Punctured or otherwise damaged brake master cylinder reservoir
^ Missing or damaged brake master cylinder filler cap gasket
^ Missing, damaged or poorly-fitted sealing grommets between the brake master cylinder and the brake master cylinder reservoir

The brake master cylinder reservoir grommets are not repairable and must be installed new as part of a new brake master cylinder reservoir.

Brake Master Cylinder - Normal Conditions
The following conditions are considered normal and are not indications that the brake master cylinder is in need of service.
Condition 1: During normal operation of the brake master cylinder, the fluid level in the brake master cylinder reservoir will rise during brake application and fall during release. The net fluid level (such as after brake application and release) will remain unchanged.
Condition 2: A trace of brake fluid will exist on the booster shell below the master cylinder mounting flange. This results from the normal lubricating action of the master cylinder bore and seal.
Condition 3: Fluid level will decrease with pad wear.

Brake Master Cylinder - Abnormal Conditions
Changes in brake pedal feel or travel are indicators that something could be wrong in the brake system. GO to Symptom Chart for abnormal condition diagnosis. Symptom Related Diagnostic Procedures

Brake Booster
Inspect the brake booster for the following:
^ Excessive corrosion or damage
^ Vacuum connections for leakage
^ Vacuum hoses for kinks or leakage
^ Brake booster check valve for correct operation

Changes in the brake pedal feel or travel are indicators that something could be wrong in the brake system. GO to Symptom Chart for abnormal condition diagnosis. Symptom Related Diagnostic Procedures

Parking Brake
Check the operation of the parking brake system with the vehicle on a hoist and the parking brake control fully released. Check for any damaged cables and install new components as necessary. Check the rear brake adjustment or carry out the brake system diagnosis.

Visual Inspection Chart:

For low or spongy brake pedal concerns:
^ check for fluid leaks. Repair as necessary.
^ check and, if necessary, refill the brake master cylinder reservoir.
^ bleed the brake system and retest the brake pedal feel.
^ if the brake pedal is still low or feels spongy, check the brake pedal mounting for looseness and correct installation. Check the power brake booster and the brake master cylinder for loose mounting. Correct as necessary and retest the system for normal operation.

For a slow or incomplete brake pedal return concern:
^ inspect for binding, damage, correct installation or interference at the brake pedal.
^ check the power brake booster for binding, damage and correct installation.