Inspection and Verification - Hydraulic Brake System

WARNING: This page is about a different car, the 2010 Lincoln Town Car. However, it is still accessible from the selected car via links, so may be relevant.

WARNING: Do not use any fluid other than clean brake fluid meeting manufacturer's specification. Additionally, do not use brake fluid that has been previously drained. Following these instructions will help prevent system contamination, brake component damage and the risk of serious 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 serious personal injury.

NOTE: 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, specified brake fluid to prevent recontamination.

NOTE: 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. Refer to INSTRUMENTATION, MESSAGE CENTER, AND WARNING CHIMES article.

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.

Verify the customer concern.

Visually inspect for obvious signs of mechanical or electrical damage.

VISUAL INSPECTION CHART

Mechanical	Electrical
Brake master cylinder Brake master cylinder reservoir Brake booster Brake booster check valve Brake booster vacuum hose Brake hoses and tubes Brake caliper Brake caliper piston seals Brake caliper guide pins Brake disc Brake pads Brake pedal linkage Wheel bearings Tires	Parking brake switch Brake fluid level switch Wiring, terminals or connectors

If an obvious cause for an observed or reported concern is found, correct the cause (if possible) before proceeding to the next step.
If the cause is not visually evident, go to Symptom Chart - Brake System or Go to Symptom Chart - Noise, Vibration and Harshness (NVH) .
For low or spongy brake pedal concerns:
- check for fluid leaks. Repair as necessary.
- check and, if necessary, refill the brake master cylinder reservoir with clean, specified brake fluid.
- 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 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.

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 specifications. It is also not required to install new brake pads when the brake discs are machined.

Remove the brake pads. Refer to FRONT DISC BRAKE article for front disc brakes or REAR DISC BRAKE article for rear disc brakes.
Inspect and measure the thickness of the brake pad friction material. Refer to Specifications in this service information.
- If there are missing chunks or cracks in the lining through to the backing plate, install new brake pads. Refer to FRONT DISC BRAKE article for front disc brakes or REAR DISC BRAKE article for rear disc brakes.
- If the thickness of the friction material is less than the specified thickness, install new brake pads. Refer to FRONT DISC BRAKE article for front disc brakes or REAR DISC BRAKE article for rear disc brakes.
- If the friction material shows taper wear that is not within specifications, verify the caliper guide pins are functioning correctly. Refer to Brake Caliper Guide Pins in this service information.

Brake Discs

NOTE: 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. Refer to FRONT DISC BRAKE article for front disc brakes or REAR DISC BRAKE article for rear disc brakes.
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, refer to Specifications in this service information.
- If the brake disc is cracked or otherwise damaged, install new a brake disc. Refer to FRONT DISC BRAKE article for front disc brakes or REAR DISC BRAKE article for rear disc brakes.
- If any thickness measurement is less than the minimum specification, install a new brake disc. Refer to FRONT DISC BRAKE article for front disc brakes or REAR DISC BRAKE article for rear disc brakes.
- If the diagnosis has revealed vibration in the steering wheel, seat or pedal while braking that varies with vehicle speed, machine the brake disc. 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 specification. Refer to Specifications and Brake Disc Machining .

Brake Calipers

Inspect the brake calipers for the following:

Brake fluid leaks. Refer to Brake System Leak Check and Non-Pressure Leaks.
Boots and seals for tears or cracks.
Caliper pistons for binding and corrosion.
Guide pins for correct operation. Refer to Brake Caliper Guide Pins in this service information.

Brake Caliper Guide Pins

NOTE: Do not use power tools for caliper guide pin bore cleaning. Damage to the bore may result.

NOTE: The guide pins are part of the anchor plate.

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, install a new brake caliper anchor plate. Refer to FRONT DISC BRAKE article for the front brake caliper anchor plate or REAR DISC BRAKE article for the rear brake caliper anchor plate.

If the lining is not within specifications, install new brake pads. Refer to FRONT DISC BRAKE article for front disc brakes or REAR DISC BRAKE article for rear disc brakes.

Brake Hoses and Tubes

NOTE: Never use copper tubing. It is subject to fatigue, cracking and corrosion, which may 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 with a new 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. Refer to Brake System Bleeding .

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

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

Non-Pressure Leaks

Two parts of the brake system that could have a brake fluid loss that does not appear when the system is under pressure are the brake master cylinder reservoir and the brake caliper under the following conditions:

Reservoir

Missing or poorly-fitted brake master cylinder filler cap
Missing or damaged brake master cylinder filler cap gasket
Punctured or otherwise damaged brake master cylinder reservoir
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 serviceable and must be installed new as part of a new reservoir assembly. Refer to Brake Fluid Reservoir in HYDRAULIC BRAKE ACTUATION article.

Caliper

Foreign material in the caliper piston seal groove
Punctured or otherwise damaged caliper piston seal

The brake caliper piston seals are not serviceable and must be installed new as part of a new brake caliper. Refer to FRONT DISC BRAKE article for front disc brakes or REAR DISC BRAKE article for rear disc brakes.

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 fall during brake application and rise 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 - Brake System for abnormal condition diagnosis.

Brake Booster

Inspect the brake booster:

for excessive corrosion or damage.
vacuum connections for leakage.
vacuum hoses for kinks or leakage.
check valve for correct operation.

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 preform the brake system diagnosis. Refer to PARKING BRAKE AND ACTUATION article.