Vacuum brake booster
- Check all hoses and connections. All unused connectors of the vacuum system must be closed with plugs. Hoses and their connections must be properly secured, in good condition, free of holes and deformed areas. Inspect the valve on the vacuum brake booster for damage.
- Check hydraulic brake system for leaks or low brake fluid.
- With the automatic transmission in the PARK position, stop the engine and apply the parking brake. Depress the brake pedal several times to release the vacuum in the system. With the engine off and no vacuum in the system, depress the brake pedal and hold it down. Start the engine. If the vacuum system is working, with continuous foot pressure, the brake pedal will tend to move down. If no movement is felt, the brake booster system is not working.
- Disconnect the vacuum hose from the vacuum brake booster. At the end of the hose on the side of the vacuum brake booster, when the engine is idling and the automatic transmission is in the PARK position, there must be a vacuum equal to the vacuum in the intake manifold. Ensure that all unused vacuum connections are properly plugged, hose connections are properly secured, and vacuum hoses are in good condition. After checking for vacuum (equal to the vacuum in the intake manifold), supplied to the vacuum brake booster, connect the vacuum hose to the vacuum brake booster and repeat steps 3. If no downward movement of the brake pedal is felt, install a new brake booster.
- Let the engine run for at least 10 seconds at high idle. Stop the engine and let the car sit still for 10 minutes. Then depress the brake pedal with a force of approximately 89 N. Pedal perception (applying the brakes) should be the same as when the engine is running. If the brake pedal feels tight (no amplification), install a new valve and then recheck. If the brake pedal still feels tight, install a new brake booster. If there is a feeling when you move the brake pedal "sponges", BLEED the brake system. For more information refer to: Bleeding the brake system (206-00 Brake System - General Information, General Procedures) / Bleeding the brake system under pressure (206-00 Brake System - General Information, General Procedures).
Master brake cylinder
Usually, the first and main sign of the presence of any malfunction in the brake system is the nature of the perception of the brake pedal. When diagnosing the condition of the master brake cylinder, check the nature of the perception of the pedal, as a sign of a malfunction in the brake system. Check the activation of the brake system warning lamp and the level of brake fluid in the reservoir of the hydraulic brake drive.
Normal states
The following conditions are considered normal and do not indicate that the master cylinder needs to be repaired.
- Modern brake systems do not have the same stiff brake pedal as they did in the past. If there is a complaint of low pedal force, compare the pedal force with that of another vehicle of the same model and year of manufacture.
- The brake fluid level will drop as the brake pads wear.
Abnormal conditions
Changes in how the brake pedal feels or moves are signs of a problem with the brake system. When diagnosing problems in the brake system, a change in the nature of the perception of the brake pedal, the inclusion of a warning lamp and a low level of brake fluid are considered a sign of problems. The following conditions are considered abnormal and indicate that the brake master cylinder needs to be repaired.
NOTE: Before performing any diagnostics, verify that the brake system warning light is working.
- The pedal goes down too fast. The reason for this may be external or internal leakage.
- The pedal goes down too slowly. The reason for this may be external or internal leakage.
- The brake pedal drops too low or feels "sponges" when pressing the pedal. This condition can be caused by a lack of brake fluid in the brake reservoir, a blockage in the reservoir cap vents, or air in the hydraulic system.
- Increased effort on the brake pedal. This could be caused by a stuck or foreign object in the pedal or pedal linkage, a defective check valve, or insufficient booster vacuum.
- The rear brakes are locked with a light pedal pressure. This can be caused by damaged brake pads, partial activation of the parking brake, a damaged ABS sensor, or a bad bearing.
- Erratic effort on the brake pedal. This condition can be caused by the brake booster or improperly installed brake pads.
- The control lamp of brake system burns. This could be caused by a low fluid level or a damaged float.
Leaks without pressure
Any reduction in the amount of fluid in the brake fluid reservoir can be caused by two types of external leaks (no pressure).
- Type 1: There may be an external leak in the brake fluid reservoir cap resulting from improper gasket and cap installation. Reinstall cover and gasket.
- Type 2: External leakage may occur at the sealing area of the brake reservoir mount. Repair such leakage by installing new seals and verify that the brake fluid reservoir mounting bolt is correctly installed.
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