The brake system is the most important link in the vehicle's safety system. It includes the service brake system and the parking brake. Maintenance and repair of brake system components requires accuracy and precision. If you do not have the necessary experience, it is better to entrust these operations to car service specialists.
The service brake system is designed to reduce the vehicle speed up to its complete stop and to keep the vehicle from rolling during short stops on a slope. All Astra-H and Zafira-B models are equipped with a hydraulic brake system with vacuum booster. It includes a master brake cylinder, a vacuum brake booster and disc brake mechanisms of the front and rear wheels. To increase reliability, the hydraulic drive of the brake mechanisms is divided into 2 independently functioning circuits, each of which is connected to diagonally located wheels of the vehicle. One brake circuit is connected to the calipers of the right front and left rear wheels, the second - to the calipers of the front left and rear right wheels. In the event of failure of one brake circuit, the second continues to operate in the previous mode, providing adequate braking of the vehicle. Failure of any of the circuits leads to a decrease in braking efficiency and is accompanied by the activation of the corresponding indicator lamp on the instrument panel (see Chapter "Controls and operating techniques", Section 16).
Fluid pressure for both circuits is created in the master brake cylinder (MBC) when the brake pedal is pressed. The MBC is mounted on the brake booster servo assembly, which is secured to the rear bulkhead of the engine compartment. A reservoir with a reserve of brake fluid is located on top of the cylinder. It is common for both the service brake system drive and the clutch drive (with appropriate equipment).
To create the required pressure in the hydraulic circuit, it is necessary to apply significant force to the brake pedal. A vacuum booster is used to facilitate control of the brake system.
On petrol models, when the brake pedal is pressed, a one-way valve opens, and one of the two air chambers of the servo drive is connected to the engine's air intake tract. Due to the movement of the air flow in the intake tract, a vacuum is created in the servo drive chamber. In the other chamber of the servo drive, the air pressure is higher and under its influence, the membrane connected to the master cylinder rod begins to move and creates the necessary additional force.
On diesel models, a special vacuum pump is used to create a vacuum in the servo drive chamber. It is mounted on the engine head and driven by the timing camshaft.
Note: On 1.7L diesel engines, the vacuum pump is mounted on the back of the generator and is driven by its shaft.
Brake pads with friction linings are the executive component of the braking system - the braking efficiency depends on their condition and the condition of the brake discs. For each car model, taking into account the configuration, pads of the corresponding brand are intended; installing other pads can lead to a change in the handling characteristics of the car, a decrease in braking efficiency and, ultimately, to an accident. Some tips and techniques for braking are given in Chapter "Controls and operating techniques".
Precautionary measures
When servicing vehicle brake components, there are some special precautions that should be taken:
- a) Use only the correct grade of hydraulic fluid to fill the brake system (see Chapter 1);
- b) Brake shoe/pad friction linings may contain asbestos, which is harmful to health. Avoid inhaling brake dust, and do not blow it off with compressed air. Never use gasoline or petroleum-based solvents to clean brake system components - use only branded cleaning agents:
- c) Ensure that all required tolerances and tightening forces are observed. When servicing components, use only serviceable tools. If in doubt, seek help from specialists. Remember that proper functioning of the brakes is the key to traffic safety;
- d) At the slightest sign of malfunction of the braking system, operation of the vehicle must be suspended!
- e) When servicing any part of the system, proceed carefully and methodically, scrupulously maintaining cleanliness. If you are not sure of the functionality of the components, replace them as a set for both brake mechanisms of each axle. Use only spare parts from well-known manufacturers.
Upon completion of maintenance and repair work on brake systems, the following points must be checked each time:
- Are the brake hoses securely fastened?
- Are the brake hoses and lines in the holders?
- Are the bleed valves tightened?
- Is there enough brake fluid in the system?
- With the engine running, check the tightness of the service brake system. To do this, press the brake pedal with a force of 200 to 300 N (20-30 kg) and hold for 30 seconds - the brake pedal should not fall or sink.
Finally, carry out test braking on the road when there are no vehicles on it.
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