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General Procedures > < Brake System - 2.0L Duratec-RS (Zetec)

Focus RS 2003 (09.2002-)

Brake System - General Information - Brake System—2.0L Duratec-RS (Zetec) Focus RS 2003 (09/2002-)
Diagnosis and Testing

Principles of Operation

The brake system operates by transferring effort applied to the brake pedal by the driver, to the brakes at each wheel.

The braking effort is distributed to each wheel, using a hydraulic system. The system is assisted using a vacuum brake booster that reduces pedal effort and increases hydraulic pressure. The parking brake operates on the rear wheels and is applied using a hand operated control.

Inspection and Verification

  1. Verify the customers concern, carrying out a road test with the customer if necessary. REFER to Section  100-00 General Information.
  1. Visually inspect for obvious signs of mechanical damage.

Visual Inspection Chart

Mechanical
  • Tire Pressure(s)
  • Wheels and tires
  • Fluid leak from brake line(s)
  • Fluid level
  • Fluid contamination
  1. If an obvious cause for an observed or reported concern is found, correct the cause (if possible) before proceeding to the next step.
  1. If the cause is not visually evident, verify the symptom and refer to the Symptom Chart.

Symptom Chart

Symptom Possible Sources Action
The brakes pull or drift
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Brake pads.
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CHECK and INSTALL new components as necessary. REFER to Section  206-03 Front Disc Brake / 206-04 Rear Disc Brake.
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Brake disc.
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CHECK and INSTALL new components as necessary. REFER to Section  206-03 Front Disc Brake / 206-04 Rear Disc Brake.
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Brake caliper.
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CHECK and INSTALL new components as necessary. REFER to Section  206-03 Front Disc Brake / 206-04 Rear Disc Brake.
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Rear brake adjustment.
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CHECK the automatic adjustment. REFER to Section  206-05 Parking Brake and Actuation.
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Wheel alignment angles.
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CHECK the wheel alignment angles. REFER to Section  204-00 Suspension System - General Information.
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Brake disc shield bolts.
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TIGHTEN or INSTALL new brake disc shield bolts. REFER to Section  206-04 Rear Disc Brake.
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Wheel bearing.
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CHECK or INSTALL a new wheel bearing. REFER to Section  204-01 Front Suspension.
The red brake warning indicator is always on
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Brake master cylinder primary piston cup.
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INSTALL a new brake master cylinder. REFER to Section  206-06 Hydraulic Brake Actuation.
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Parking brake control.
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RELEASE and ADJUST the parking brake. REFER to Section  206-05 Parking Brake and Actuation.
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Brake fluid level sensor.
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REFER to WDS.
Vibration when brakes are applied
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Brake pads.
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CHECK and INSTALL new components as necessary. REFER to Section  206-03 Front Disc Brake / 206-04 Rear Disc Brake.
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Brake disc.
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CHECK and INSTALL new components as necessary. REFER to Section  206-03 Front Disc Brake / 206-04 Rear Disc Brake.
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Brake caliper.
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CHECK and INSTALL new components as necessary. REFER to Section  206-03 Front Disc Brake / 206-04 Rear Disc Brake.
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Wheel bearings.
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CHECK or INSTALL a new wheel bearing. REFER to Section  204-01 Front Suspension / 204-02 Rear Suspension.
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Wheel balance.
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CHECK and BALANCE the wheels and tires as necessary.
The pedal goes down fast
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Air in the brake system.
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BLEED the brakes. REFER to Section  206-00 Brake System - General Information.
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Brake master cylinder.
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Carry out the brake master cylinder component test in this section.
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Brake disc.
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CHECK and INSTALL new components as necessary. REFER to Section  206-03 Front Disc Brake / 206-04 Rear Disc Brake.
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Brake pads.
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CHECK and INSTALL new components as necessary. REFER to Section  206-03 Front Disc Brake / 206-04 Rear Disc Brake.
The pedal eases down slowly
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Air in the brake system.
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BLEED the brakes. REFER to Section  206-00 Brake System - General Information.
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Brake master cylinder.
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Carry out the brake master cylinder component test in this section.
The pedal is low or feels spongy
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Air in the brake system.
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BLEED the brakes. REFER to Section  206-00 Brake System - General Information.
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Brake pads.
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CHECK and INSTALL new components as necessary. REFER to Section  206-03 Front Disc Brake / 206-04 Rear Disc Brake.
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Brake booster
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CARRY out the brake booster component test in this section.
Brake lockup during light brake pedal force
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Brake pads.
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CHECK and INSTALL new components as necessary. REFER to Section  206-03 Front Disc Brake / 206-04 Rear Disc Brake.
*
Brake caliper.
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CHECK and INSTALL new components as necessary. REFER to Section  206-03 Front Disc Brake / 206-04 Rear Disc Brake.
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Brake disc.
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CHECK and INSTALL new components as necessary. REFER to Section  206-03 Front Disc Brake / 206-04 Rear Disc Brake.
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Brake booster
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CARRY out the brake booster component test in this section.
Excessive/erratic brake pedal travel
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Brake pads.
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CHECK and INSTALL new components as necessary. REFER to Section  206-03 Front Disc Brake / 206-04 Rear Disc Brake.
*
Brake disc.
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CHECK and INSTALL new components as necessary. REFER to Section  206-03 Front Disc Brake / 206-04 Rear Disc Brake.
*
Wheel bearings.
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CHECK or INSTALL a new wheel bearing. REFER to Section  204-01 Front Suspension / 204-02 Rear Suspension.
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Brake booster
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CARRY out the brake booster component test in this section.
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Brake pedal
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REPAIR or INSTALL a new brake pedal and bracket. REFER to Section  206-06 Hydraulic Brake Actuation.
Brakes drag
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Brake booster.
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CARRY out the brake booster component test in this section.
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Brake caliper.
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CHECK and INSTALL new components as necessary. REFER to Section  206-03 Front Disc Brake / 206-04 Rear Disc Brake.
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Parking brake control.
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CHECK and INSTALL new components as necessary. REFER to Section  206-05 Parking Brake and Actuation.
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Parking brake cable.
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CHECK and INSTALL new components as necessary. REFER to Section  206-05 Parking Brake and Actuation.
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Brake pedal
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REPAIR or a INSTALL new brake pedal and bracket. REFER to Section  206-06 Hydraulic Brake Actuation.
Excessive brake pedal effort
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Brake booster.
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CARRY out the brake booster component test in this section.
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Brake pads.
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CHECK and INSTALL new components as necessary. REFER to Section  206-03 Front Disc Brake / 206-04 Rear Disc Brake.
*
Brake pedal
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REPAIR or a INSTALL new brake pedal and bracket. REFER to Section  206-06 Hydraulic Brake Actuation.
Slow or incomplete brake pedal return
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Brake booster.
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CARRY out the brake booster component test in this section.
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Brake master cylinder.
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Carry out the brake master cylinder component test in this section.
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Brake pedal
*
REPAIR or a INSTALL new brake pedal and bracket. REFER to Section  206-06 Hydraulic Brake Actuation.

Component Tests

Brake Booster

  1. Inspect all hoses and connections. All unused vacuum connectors should be capped. Hoses and their connections should be correctly secured and in good condition with no holes and no collapsed areas. Inspect the brake booster check valve for damage.
  1. Check the hydraulic brake system for leaks or low fluid.
  1. With the transmission in NEUTRAL, stop the engine and operate the parking brake. Operate the brake pedal several times to exhaust all vacuum in the system.
  1. With the engine turned OFF and all vacuum in the system exhausted, operate the brake pedal and hold it down. Start the engine. If the vacuum system is operating, the brake pedal will tend to move downwards under constant foot pressure. If no motion is felt, the vacuum booster system is not functioning.
  1. Remove the vacuum hose from the brake booster. Manifold vacuum should be available at the brake booster end of the hose with the engine at idle speed and the transmission in NEUTRAL. Make sure that all unused vacuum outlets are correctly capped, hose connectors are correctly secured and vacuum hoses are in good condition. When it is established that manifold vacuum is available to the brake booster connect the vacuum hose to the brake booster and repeat Step 3. If no downward movement of the brake pedal is felt, the vacuum booster system is not functioning.
  1. Run the engine for a minimum of 10 seconds at fast idle. Stop the engine and let the vehicle stand for 10 minutes. Then, operate the brake pedal with approximately 89 N (20 lb) of force. The pedal feel (brake applications) should be the same as noted with the engine running. If the brake pedal feels hard (no power assist), install a new check valve and then repeat the testing. If the brake pedal still feels hard, install a new brake booster. If the brake pedal movement feels spongy, bleed the brake system. Refer to General Procedures.

Brake Master Cylinder

Usually, the first and strongest indicator of anything wrong in the brake system is a feeling through the brake pedal. In diagnosing the condition of the brake master cylinder, check brake pedal feel as evidence of a brake concern. Check for brake warning indicator illumination and the brake fluid level in the brake fluid reservoir.

Normal Conditions

The following conditions are considered normal and are not indications that the brake master cylinder is in need of repair.

  • New brake systems are not designed to produce as hard a pedal effort as in the past. Complaints of light pedal effort should be compared to pedal efforts of another vehicle, same model and year.
  • During normal operation of the brake master cylinder, the brake fluid level in the reservoir will rise during brake application and fall during release. The net brake fluid level (after brake application and release) will remain unchanged.
  • A trace of brake fluid exists on the brake booster shell below the master cylinder mounting flange. This results from the normal lubricating action of the master cylinder bore end seal.
  • Brake fluid level will fall with brake pad wear.

Abnormal Conditions

NOTE:
NOTE:Before carrying out any diagnosis, make sure the brake system warning indicator is functional.

Changes in brake pedal feel or travel are indicators that something could be wrong in the brake system. The diagnostic procedure and techniques are brake pedal feel, brake warning indicator illumination and low brake fluid level as indicators in diagnosing brake system concerns. The following conditions are considered abnormal and indicate that the brake master cylinder is in need of repair.

  • Brake pedal goes down fast. This could be caused by an external or internal leak.
  • Brake pedal eases down slowly. This could be caused by an external or internal leak.
  • Brake pedal is low or feels spongy. This condition may be caused by no fluid in the brake master cylinder reservoir, brake fluid reservoir cap vent holes blocked or air in the hydraulic system.
  • Brake pedal effort is excessive. This may be caused by a bind or obstruction in pedal or linkage, blocked fluid control valve or insufficient brake booster vacuum.
  • Rear brakes lock up during light pedal force. This may be caused by grease or fluid on brake pads, damaged brake pads, incorrectly adjusted parking brakes, damaged or contaminated brake pressure control valve.
  • Brake pedal effort erratic. This condition could be caused by the brake booster being inoperative, extreme brake caliper piston knock back or incorrectly installed brake pads.
  • Brake warning indicator is always ON. This may be caused by low fluid level, ignition wire routing too close to the fluid level indicator, or float assembly damage.

Bypass Condition Test

  • Check the brake fluid level in the brake fluid reservoir. Fill the brake fluid reservoir to the MAX mark if low or empty.
  • Observe the brake fluid level in the brake fluid reservoir. If after several brake applications, the brake fluid level remains the same, measure the wheel turning torque required to rotate the wheels with the brakes applied as follows:

Place the transmission in NEUTRAL and raise and support the vehicle. REFER to Section  100-02 Jacking and Lifting.

Apply the brakes with a mimimum of 445 N (100 lb) and hold approximately 15 seconds. With the brakes still appied, exert a torque on the front wheels of 10.1 Nm (75 lb/ft). If either wheel rotates, install a new brake master cylinder.

Non-Pressure Leaks

Any empty brake fluid reservoir condition may be the result of two types of non-pressure external leaks.

Type 1: An external leak may occur at the brake fluid reservoir cap because of incorrect positioning of the gasket and cap.

Reposition of the gasket and cap.

Type 2: An external leak may occur at the brake fluid reservoir mounting seals. Repair such a leak by installing new seals.

General Procedures > < Brake System - 2.0L Duratec-RS (Zetec)