The working system is double-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 working brake system fails, the second circuit is used, which ensures that the car stops with sufficient efficiency.
A vacuum booster is included in the hydraulic drive. All cars are equipped with anti-lock brakes (ABS) with a subsystem of exchange rate stability (ESP).
Parking brake system - with a cable drive to the brake mechanisms of the rear wheels. By request, the car can be equipped with an electric parking brake.
Pic. 1. Front wheel brake: 1 - brake hose; 2 - air release valve; 3 - caliper guide pin (covered with a protective cover); 4 - guide pads; 5 - brake caliper; 6 - brake disc; 7 - brake pads (the outer pad is not visible, as it is closed by the caliper)
Front wheel brakes disk, with automatic adjustment of the gap between the pads 7 (pic. 1) and disk 6, with a floating bracket. The movable bracket is formed by a caliper 5 with a single-piston working cylinder. The shoe guide 4 is bolted to the steering knuckle. The movable bracket is bolted to the guide pins 3 installed in the holes of the guide shoe. The guide pins are grease lubricated 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, the optimal clearance between the pads and the ventilated disc is maintained. When braking, the piston, under the influence of fluid pressure, presses the inner pad against the disc, as a result of the reaction force, the caliper moves on the fingers and the outer pad is also pressed against the disc, while the pressing force of the pads is the same. When releasing the piston, due to the elasticity of the sealing ring, it is retracted from the pad and a small gap is formed between the pads and the disc.
Pic. 2. Brake master cylinder with reservoir: 1 - the main brake cylinder; 2 – a tank of the main brake cylinder; 3 - brake fluid level sensor; 4 – tank fastening screw; 5 - connecting bushings; 6 – a sealing ring of a flange of the main brake cylinder
Master brake cylinder 1 (pic. 2) type «tandem» The hydraulic brake actuator 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.
Tank 2 is installed on the main cylinder through rubber connecting bushings 5, the internal cavity of which is divided by partitions into three compartments. Each compartment feeds one of the brake master cylinder chambers and the clutch release master cylinder.
When you press the brake pedal, the pistons of the main brake cylinder begin to move, the working edges of the cuffs cover the compensation holes, the chambers and the reservoir are separated and the brake fluid is forced out.
Brake fluid level sensor 3 is installed in the upper half of the tank body. If the fluid level falls below the permissible level, the warning lamp for a malfunctioning brake system lights up in the instrument cluster. The connection of the main brake cylinder with the vacuum brake booster is sealed with a rubber ring 6.
Pic. 3. Vacuum booster
vacuum booster (pic. 3), installed between the pedal mechanism and the main brake cylinder, when braking due to rarefaction in the engine intake pipe through the rod and piston of the first chamber of the main cylinder, it creates an additional force proportional to the force from the pedal.
On the Opel Astra J car, in order to guarantee the maximum vacuum value in the vacuum booster at all engine operating modes, an additional electric vacuum pump is installed, connected by a hose to the check valve of the main hose from the booster to the intake pipe.
A non-return valve is installed in the hose connecting the vacuum booster to the intake pipe. It holds the vacuum in the booster as it drops down the intake pipe.
The peculiarity of the Opel Astra J vacuum booster check valve is that it serves as a tee for connecting hoses from the intake pipe and the vacuum pump, and also acts as an electrically driven switching device, 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 not be sufficient for efficient operation of the amplifier. In this mode, the check valve closes the hose to the intake pipe and fully opens the hose to the vacuum pump.
Pic. 4. Rear wheel brake: 1 - brake caliper; 2 - brake disc; 3 - guide pads; 4 - brake pads; 5 - caliper guide pins; 6 - brake hose; 7 - air release valve; 8 – parking brake drive mechanism; 9 – a plug of the place of installation of the solenoid of the electric drive of the parking brake (electric drive installed on request)
Rear wheel brakes disc, with automatic clearance adjustment, are almost similar in design to the brake mechanisms of the front wheels. Brake pads 4 (pic. 4) powered by a single hydraulic working cylinder. The optimal clearance between the disc and the pads is maintained according to the same principle as the brake mechanisms of the front wheels. The difference between the rear wheel brake mechanism and the front brake mechanism is in a non-ventilated brake disc and in an additional parking brake drive mechanism. A feature of the Opel Astra J car is the ability to install an electric parking brake controlled by a button located on the lining of the floor tunnel instead of a lever. In this case, instead of plugs 9, solenoids are installed on the lower brackets of the guide pads of both brake mechanisms, which move the calipers when power is applied and thereby brake the car in the parking lot.
Parking brake, driven mechanically, consists of a lever, traction with an equalizer and an adjusting device, two rear cables and mechanisms on the rear wheels. The spreading lever of the parking brake drive mechanism 8, mounted on the rear wheel disc brake caliper, is acted upon by the rear drive cable. The parking brake drive mechanism acts directly on the brake pads 4 of the working brake mechanism. Moving, the expanding levers move the pistons of the brake cylinders, then through them they shift the inner brake pads until they stop at the brake discs and, having received a hard stop, move the calipers together with the outer pads, also pressing them against the discs and blocking the discs.
The parking brake lever, fixed between the front seats on the floor tunnel, is connected to a rod, combined with an equalizer, having a threaded shank for adjusting the tension of the cables. The front tips of the rear cables are connected to the equalizer.
The parking brake does not require special care. During current repairs, check the degree of wear of its parts, make sure that the teeth of the sector and the pawl are in good condition. Replace excessively worn parts.
If a break in the sheaths or wires of the cables is found, replace them with new ones.
Anti-Lock Braking System (ABS) with a subsystem of exchange rate stability (ESP) described in sect. Security systems (see Anti-Lock Braking System).
Hydraulic brake system united into a single whole by metal tubes and hoses. The system is filled with a special brake fluid of at least DOT-4 class, which must be replaced periodically. The procedure for replacing the brake fluid is described in subsection Brake Fluid Replacement.
Checking the brake system is described below (see Checking the brake system).
Helpful Hints
Some drivers, in an effort to wear out the parking brake cables less, try to use them less often. Such «saving» leads to the opposite result: the cable, rarely moving in the shell, gradually loses mobility, it jams, as a result, the cable breaks. Therefore, use the parking brake whenever necessary.
If the brake pedal always starts to vibrate when braking, most likely the brake discs are warped. Unfortunately, in such a situation, they only need to be changed, and both at once. Periodically appearing and disappearing vibration of the pedal during hard braking accompanies the operation of the anti-lock brake system and is not a sign of a malfunction.
If the car starts to pull to the side when braking, check the working cylinders: they may need to be replaced.
If there is a knock in the front suspension that disappears when braking, check the tightness of the caliper mounting bolts.
After replacing the brake pads, before driving, be sure to press the brake pedal several times - the pistons in the working cylinders should fall into place.
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