The working system is dual-circuit, with a diagonal connection of the brake mechanisms of the front and rear wheels. One hydraulic drive circuit ensures the operation of the right front and left rear brake mechanisms, the other - the left front and right rear.
If one of the circuits of the service brake system fails, the second circuit is used, ensuring that the vehicle stops with sufficient efficiency.
The hydraulic drive includes a vacuum booster. All cars are equipped with an anti-lock braking system (ABS) with an electronic stability program (ESP).
Parking brake system - with cable drive to the brake mechanisms of the rear wheels. An electric parking brake drive can be installed on the car upon request.
Fig. 1. Front wheel brake mechanism: 1 – brake hose; 2 – air release valve; 3 – caliper guide pin (covered with a protective cover); 4 – shoe guide; 5 – brake caliper; 6 – brake disc; 7 – brake pads (the outer pad is not visible as it is covered by the caliper)
Front wheel brakes disc, with automatic adjustment of the gap between the pads 7 (Fig. 1) and the disk 6, with a floating bracket. The movable bracket is formed by the support 5 with a single-piston working cylinder. The guide 4 of the pads is attached with bolts to the steering knuckle. The movable bracket is fastened with bolts to the guide pins 3 installed in the holes of the guide of the pads. The guide pins are lubricated with consistent grease and protected by rubber boots. A piston with a sealing ring is installed in the cavity of the working cylinder. Due to the elasticity of this ring, an optimal gap is maintained between the pads and the ventilated disk. When braking, the piston, under the influence of fluid pressure, presses the inner pad to the disk, as a result of the reaction force, the caliper moves on the pins and the outer pad is also pressed to the disk, while the pressing force of the pads is the same. When releasing the brakes, the piston is moved away from the pad due to the elasticity of the sealing ring, and a small gap is formed between the pads and the disc.
Fig. 2. Master brake cylinder with reservoir: 1 – main brake cylinder; 2 – master brake cylinder reservoir; 3 – brake fluid level sensor; 4 – screw for fastening the tank; 5 – connecting bushings; 6 – sealing ring of the brake master cylinder flange
Master brake cylinder 1 (Fig. 2) of the "tandem" type of hydraulic brake drive consists of two separate chambers connected to independent hydraulic circuits. The first chamber is connected to the right front and left rear brake mechanisms, the second - to the left front and right rear.
A reservoir 2 is installed on the master cylinder via rubber connecting bushings 5, the internal cavity of which is divided by partitions into three sections. Each section supplies one of the chambers of the master brake cylinder and the master cylinder of the clutch release drive.
When you press the brake pedal, the pistons of the master brake cylinder begin to move, the working edges of the cuffs cover the compensation holes, the chambers and the reservoir are separated and the displacement of the brake fluid begins.
The brake fluid level sensor 3 is installed in the upper half of the reservoir body. When the fluid level drops below the permissible level, the brake system malfunction indicator lamp lights up in the instrument cluster. The connection between the master brake cylinder and the brake booster is sealed with a rubber ring 6.
Fig. 3. Vacuum amplifier
Vacuum booster (Fig. 3), installed between the pedal mechanism and the main brake cylinder, during braking, due to the vacuum in the engine intake pipe through the rod and piston of the first chamber of the main cylinder, creates additional force proportional to the force from the pedal.
In order to guarantee the maximum vacuum value in the vacuum booster in all engine operating modes, the Opel Astra J is additionally equipped with an electric vacuum pump connected by a hose to the check valve of the main hose from the booster to the intake pipe.
A check valve is installed in the hose connecting the vacuum booster to the intake pipe. It maintains the vacuum in the booster when it drops in the intake pipe.
The peculiarity of the Opel Astra J vacuum booster check valve is that it serves as a tee for connecting the hoses from the intake pipe and the vacuum pump, and also performs the function of a switching device with an electric drive, connecting these hoses to the vacuum booster in turn depending on the operating conditions of the car. At high loads and a large throttle opening angle, the vacuum in the intake pipe is small and may be insufficient for the effective operation of the booster. In this mode, the check valve closes the hose to the intake pipe and completely opens the hose to the vacuum pump.
Fig. 4. Rear wheel brake mechanism: 1 – brake caliper; 2 – brake disc; 3 – shoe guide; 4 – brake pads; 5 – caliper guide pins; 6 – brake hose; 7 – air release valve; 8 – parking brake drive mechanism; 9 – plug for installation location of the electric parking brake solenoid (electric drive is installed upon request)
Rear wheel brakes disc, with automatic clearance adjustment, are practically identical in design to the front wheel brake mechanisms. Brake pads 4 (Fig. 4) are driven by one hydraulic working cylinder. The optimum clearance between the disc and the pads is maintained according to the same principle as that of the front wheel brake mechanisms. The difference between the rear wheel brake mechanism and the front brake mechanism is in the non-ventilated brake disc and in the additional parking brake drive mechanism. A special feature of the Opel Astra J is the ability to install an electric parking brake drive controlled by a button located on the floor tunnel lining instead of a lever. In this case, solenoids are installed on the lower brackets of the guide pads of both brake mechanisms instead of plugs 9, which move the calipers when power is supplied and thereby brake the car when parked.
Parking brake mechanism, driven mechanically, consists of a lever, a rod with an equalizer and an adjusting device, two rear cables and mechanisms on the rear wheels. The rear drive cable acts on the release lever of the parking brake drive mechanism 8, mounted on the caliper of the rear wheel disc brake mechanism. The parking brake drive mechanism acts directly on the brake shoes 4 of the service brake mechanism. When moving, the release levers move the pistons of the brake cylinders, then through them they shift the inner brake shoes until they stop against the brake discs and, having received a rigid stop, they move the calipers together with the outer shoes, also pressing them against the discs and blocking the discs.
The parking brake actuator lever, secured between the front seats on the floor tunnel, is connected to a rod combined with an equalizer, which has a threaded tailpiece for adjusting the tension of the cables. The front ends of the rear cables are connected to the equalizer.
The parking brake does not require special maintenance. During routine repairs, check the degree of wear of its parts, make sure that the sector teeth and pawl are in good condition. Replace excessively worn parts.
If any breaks in the cable sheaths or wires are detected, replace them with new ones.
Anti-lock braking system (ABS) with electronic stability program (ESP) described in the section Security systems (see Anti-lock braking system).
Hydraulic brake system is united into a single whole by metal tubes and hoses. The system is filled with a special brake fluid of a class not lower than DOT-4, which must be replaced periodically. The procedure for replacing the brake fluid is described in the subsection Replacing brake fluid.
Checking the brake system is described below (see Checking the brake system).
Useful tips
Some drivers, trying to wear out the parking brake cables less, try to use them less often. Such "savings" lead to the opposite result: the cable, rarely moving in the casing, gradually loses mobility, it jams, and as a result the cable breaks. Therefore, use the parking brake in all cases when it is necessary.
If the brake pedal always starts to vibrate when braking, the brake discs are most likely warped. Unfortunately, in this situation, they only need to be replaced, and both at once. Periodically appearing and disappearing vibration of the pedal during sharp braking accompanies the operation of the anti-lock braking system and is not a sign of a malfunction.
If the car starts to pull to one side when braking, check the wheel cylinders: they may need to be replaced.
If a knocking noise appears in the front suspension that disappears when braking, check the tightness of the caliper mounting bolts.
After replacing the brake pads, before starting to move, be sure to press the brake pedal several times - the pistons in the working cylinders should fall into place.
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