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Ford Kuga
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Brake System - General Information » Brake System
Brake Booster Functional Test

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 check valve on the brake booster for damage.

Brake Booster Operation Check

1. Check the hydraulic brake system for leaks or low fluid.

2. With the transaxle in the NEUTRAL position, stop the engine and apply the parking brake.

Apply the brake pedal several times to exhaust all the vacuum in the system.

3. With the engine turned off and the vacuum in the system exhausted, apply the brake pedal and hold it down. Start the engine. If the vacuum system is operating, the brake pedal will tend to move downward under constant foot pressure. If no motion is felt, the vacuum booster system is not functioning.

4. 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 transaxle in the NEUTRAL position. 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, install a new brake booster.

5. Operate the engine a minimum of 10 seconds at approximately 1200 rpm. Stop the engine and let the vehicle stand for 10 minutes. Then, apply the brake pedal with approximately 89 N (20 lb) force. The pedal feel (brake application) should be the same as that noted with the engine operating. If the brake pedal feels hard (no power assist), install a new vacuum check valve and then repeat the test. 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: (206-00 Brake System - General Information) Brake System Bleeding (General Procedures), Brake System Pressure Bleeding (General Procedures), Component Bleeding (General Procedures).

Brake Master Cylinder

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

Normal Conditions

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

  • Modern brake systems are not designed to produce as hard a pedal effort as in the past.

    Complaints of light pedal efforts should be compared to pedal efforts of another vehicle, of the same model and year.

  • During normal operation of the brake pedal, the fluid level in the reservoir will rise during brake pedal application and fall during release. The net fluid level (i.e., after brake pedal application and release) will remain unchanged.
  • A trace of brake fluid will 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.
  • The fluid level will fall with brake shoe and lining wear.

Abnormal Conditions

NOTE: Prior to performing 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 with the braking system. The diagnostic procedure and techniques use brake pedal feel, warning indicator illumination and low brake fluid level as indicators in diagnosing braking system concerns. The following conditions are considered abnormal and indicate that the brake master cylinder is in need of service.

  • The brake pedal goes down fast. This could be caused by an external or internal leak.
  • The brake pedal eases down slowly. This could be caused by an external or internal leak.
  • The brake pedal is low and or feels spongy. This condition may be caused by no fluid in the brake master cylinder reservoir, reservoir cap vent holes clogged or air in the hydraulic system.
  • The brake pedal effort is excessive. This may be caused by a bind or obstruction in the pedal or linkage, clogged fluid control valve or insufficient booster vacuum.
  • The rear brakes lock up during light pedal force.

    This may be caused by incorrect tire pressures, grease or fluid on the brake shoes and linings, damaged brake shoes and linings, incorrectly adjusted parking brake, or damaged or contaminated brake pressure control valves.

  • The brake pedal effort is erratic. This condition could be caused by a brake booster malfunction, extreme caliper piston knock back or incorrectly installed brake shoes and linings.
  • The red brake warning indicator is ON. This may be caused by low fluid level, ignition wire routing too close to the fluid level indicator assembly, or float assembly damage.

Bypass Condition Test

1. Check the fluid in the brake master cylinder reservoir. Fill the brake master cylinder reservoir if low or empty.

2. Observe the fluid level in the brake master cylinder reservoir. If after several brake applications, the fluid level remains the same, measure the wheel turning torque required to rotate the wheels with the brakes applied as follows: Place the transaxle in the NEUTRAL position.

Raise and support the vehicle. REFER to: (100-02 Jacking and Lifting) Jacking (Description and Operation), Lifting (Description and Operation).

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

REFER to: Brake Master Cylinder - 2.5L Duratec (147kW/200PS) - VI5 (206-06 Hydraulic Brake Actuation, Removal and Installation).

Non-Pressure Leaks

Any empty brake master cylinder reservoir condition may be caused by two types of non-pressure external leaks.

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

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

    More about «Brake System»:

    Inspection and Verification

    Road Test

    Pinpoint Tests

    Component Tests

    Brake System Check

    Brake Booster Functional Test

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