Features of the brake system

The Chevrolet Cruze is equipped with two independent brake systems: working and parking. The first, equipped with a hydraulic drive, provides braking when the car is moving, the second slows down the car in the parking lot. 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 left front and right rear.

If one of the circuits of the service brake system fails, another circuit is used to stop the vehicle with sufficient efficiency.

The main brake cylinder 23 is included in the hydraulic drive (pic. 9.1), vacuum booster 5, hydroelectronic module 22 of the anti-lock braking system, brake mechanisms of the front and rear wheels together with working cylinders, pipelines.




Parking brake system with cable drive on the brake mechanisms of the rear wheels.

Brake mechanism of the front wheel disc, with automatic adjustment of the gap between the pads 10 (pic. 9.2) and disk 1, with a floating bracket. The movable bracket is formed by a caliper 11 with a single-piston working cylinder. The shoe guide 2 is bolted to the steering knuckle. The caliper is attached with bolts 4 and 7 to the guide pins installed in the holes of the guide pads. The guide pins are grease lubricated and protected by rubber boots. A piston with a sealing ring is installed in the cavity of the wheel cylinder. Due to the elasticity of this ring, an optimal clearance is maintained between the pads and the ventilated disc, the surface of which is protected by the brake shield. 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 the piston is released, due to the elasticity of the sealing ring, a small gap is formed between the pads and the disc.




Master brake cylinder 4 (pic. 9.3) 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 brakes, the second to the left front and right rear.



Tank 2 is installed on the main cylinder through rubber connecting bushings, 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.

The brake fluid level sensor 1 is installed in the tank housing. If the fluid level falls below the permissible level, the warning lamp for a malfunctioning brake system lights up in the instrument cluster.


The vacuum booster 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, creates an additional force proportional to the force from the pedal.

A non-return valve is adopted 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 vacuum brake booster is the most common type of booster that is used in the brake system of a modern car. It creates additional force on the brake pedal due to vacuum. The use of an amplifier greatly facilitates the work of the vehicle's braking system and thereby reduces driver fatigue.

Structurally, the vacuum booster forms a single unit with the main brake cylinder.

Note: Replacing the vacuum booster is not described in this section due to the fact that during this operation it is necessary to remove the ABS hydro-electronic unit. Work on the removal of the hydro-electronic unit is recommended to be carried out in specialized service centers.

The brake mechanism of a back wheel is disk, with automatic adjustment of a backlash. Brake pads 9 and 10 (pic. 9.4) 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 disc working brake mechanism of the rear wheel is combined with the parking brake mechanism. The inner cavity of the brake disc also serves as the parking brake disc.

The mechanically actuated parking brake consists of a lever, an adjusting device, two rear cables and brakes on the rear wheels.

Anti-Lock Braking System (ABS) consists of wheel speed sensors, brake pedal switch, hydroelectronic control module (HECU) and signal lamp in the instrument cluster. The anti-lock braking system is also equipped with a self-diagnosis system that detects malfunctions of system components.

ABS is used to regulate the pressure in the brake mechanisms of all wheels when braking in difficult road conditions, preventing the wheels from locking.

The ABS system provides the following benefits:

• avoiding obstacles with a higher degree of safety, including during emergency braking;
• shortening the braking distance during emergency braking while maintaining roadholding and vehicle controllability. including turning.

In the event of a system failure, functions for diagnosing and maintaining operation in case of system failures are provided.

The hydroelectronic control module receives information about vehicle speed, direction of travel and road conditions from wheel speed sensors, steering wheel angle sensor, throttle position sensor. After the ignition is switched on, the control unit supplies voltage to the wheel speed sensors. The sensors use the Hall effect, they generate an output signal in the form of rectangular pulses. The signal changes in proportion to the rotational speed of the sensor's pulse ring mounted on the wheel drive outer joint housing.

Based on this information, the control unit determines the optimal wheel braking mode.

There are the following modes of operation of the anti-lock braking system:

• normal braking mode. During normal braking, the solenoid valve is de-energized, the inlet valve is open, the outlet valve is closed. When the brake pedal is pressed, pressurized brake fluid is supplied to the working cylinder through the solenoid valve and actuates the wheel brakes. When the brake pedal is released, the brake fluid returns to the brake master cylinder through the inlet and check valves;
• emergency braking mode. If a wheel lock occurs during emergency braking, the module issues a command to the solenoid valve to reduce the supply of brake fluid, then voltage is applied to each solenoid valve. The inlet valve closes and the brake fluid supply from the master cylinder is shut off; the outlet valve opens, and the brake fluid flows from the working cylinder to the master cylinder, and then to the reservoir, which causes a decrease in pressure;
• pressure maintenance mode. When the pressure in the working cylinder is reduced to the maximum, the module issues a command to the solenoid valve to maintain brake fluid pressure, voltage is applied to the inlet valve and is not applied to the outlet valve. At the same time, the inlet and outlet valves are closed and the brake fluid does not leave the working cylinder;
• pressure boost mode. If the module determines that the wheel is not blocked, then it de-energizes the solenoid valve. Voltage is not applied to the solenoid valves, the brake fluid through the inlet valve enters the working cylinder, the pressure in which increases.

Diagnostics and repair of the anti-lock braking system requires special equipment and accessories. Therefore, in case of failure, contact a specialized service station.

Helpful Hints: Too short travel indicates incorrect initial setting of the brake pedal, misadjustment of the vacuum brake booster or seizure of the working cylinder, causes increased fuel consumption and accelerated wear of the brake pads. Too large a stroke is a sign of excessive clearances in the pedal mechanism or a violation of the tightness of the hydraulic drive of the brake system. If the stroke decreases when the pedal is pressed repeatedly, i.e. she becomes «tougher», - air in the system. If the full pedal travel starts to increase, the system is leaking.

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.