Renault / Dacia Sandero is equipped with two independent braking systems: working and parking.

The first, equipped with a hydraulic drive with a vacuum booster, provides braking when the car is moving, the second brakes the car in the parking lot.

The working system is double-circuit with a diagonal connection of the brakes of the front and rear wheels.

One circuit of the hydraulic drive provides the operation of the right front and left rear brakes, the other - the left front and right rear.

If one of the circuits of the service braking system fails, a second circuit is used to stop the vehicle with sufficient efficiency.

The brake pedal is of the suspended type.

A brake signal switch is installed in the pedal assembly bracket above the brake pedal - its contacts close when the pedal is pressed.

Особенности тормозов автомобиля Рено Сандеро

To reduce the effort on the brake pedal, a vacuum booster is used, which uses a vacuum in the receiver of a running engine.

The vacuum booster is located in the engine compartment between the pedal pusher and the brake master cylinder and is secured with four nuts (through the bulkhead) to the pedal bracket.

The vacuum amplifier is non-separable; if it fails, it is replaced.

Особенности тормозов автомобиля Рено Сандеро

The main brake cylinder is fastened with nuts to two pins of the vacuum booster housing.

On top of the cylinder there is a reservoir for the hydraulic drive of the brake system, which contains a supply of working fluid.

On the body of the tank, there are marks of the maximum and minimum liquid levels, and in the upper part there is a sensor that, when the liquid level drops below the MIN mark, turns on the indicator in the instrument cluster.

When the brake pedal is pressed, the pistons of the master cylinder move, creating pressure in the hydraulic drive, which is supplied through pipes and hoses to the working cylinders of the wheel brake mechanisms.

Особенности тормозов автомобиля Рено Сандеро

The front wheel brake mechanism is a disc, with a floating caliper, including a caliper, made together with a single-piston wheel cylinder.

The brake shoe guide is bolted to the steering knuckle with two bolts, and the caliper is attached with two bolts to the guide pins installed in the shoe guide holes.

Protective rubber covers are installed on the fingers.

Grease is placed in the pin holes of the shoe guides.

When braking, the fluid pressure in the hydraulic drive of the brake mechanism increases and the piston, moving out of the wheel cylinder, presses the inner brake shoe against the disc.

Then the caliper (due to the movement of the guide pins in the holes of the shoe guide) moves relative to the disc, pressing the outer brake shoe against it.

A piston with a rectangular rubber sealing ring is installed in the cylinder body.

Due to the elasticity of this ring, a constant optimum clearance is maintained between the disc and the brake pads.

Особенности тормозов автомобиля Рено Сандеро

Rear wheel brake - drum, with a two-piston wheel cylinder and two brake pads, with automatic adjustment of the gap between the pads and the drum.

The brake drum is at the same time the hub of the rear wheel and the bearing is pressed into it.

Особенности тормозов автомобиля Рено Сандеро

The pressure regulator changes the pressure in the hydraulic drive of the rear wheel brakes, depending on the load on the rear axle of the vehicle.

It is included in both circuits of the brake system, through which the brake fluid is supplied to both rear brakes.

The regulator is bolted to the vehicle body. Its rod is connected to the rear suspension beam through a spring-loaded load rod, lever 4 and a shackle.

Depending on the distance between the beam and the body, which depends on the load of the car, the regulator rod moves, which, in turn, with the help of a system of valves, changes the cross-sectional area of ​​the passage channels of the circuits inside the regulator, thereby limiting the pressure in the rear brake circuits.

The degree of restriction of the regulator, and, consequently, the pressure in the circuits is regulated by changing the length of the regulator stem with a nut.

The wheel cylinders of the rear wheel brakes are the same.

The front brake pads of the rear wheels are the same, but the rear ones are different - they are mirror-symmetrically fitted with non-removable levers for the parking brake drive.

The spacer bar and ratchet nut of the brakes on the left and right wheels are different.

The ratchet nut and the tip of the left wheel spacer have a left-hand thread, and the ratchet nut and the tip of the right wheel spacer have a right-hand thread.

The levers of the brake adjusters of the left and right wheels are mirror-symmetrical.

Особенности тормозов автомобиля Рено Сандеро

The anti-lock braking system (ABS) consists of a hydroelectronic unit 1 (Fig. 6) with hydraulic solenoid valves, wheel speed sensors, an electrically driven pump and a warning light 4 in the instrument cluster.

The anti-lock braking system is used to regulate the pressure in the braking mechanisms of all wheels when braking in difficult road conditions, preventing the wheels from locking. ABS provides the following benefits:

- obstacle avoidance with a higher degree of safety, including during emergency braking;

- reduction of the braking distance during emergency braking while maintaining directional stability and controllability of the vehicle, including when cornering.

In the event of a system malfunction, there is a function to maintain operation in the event of system failures.

The hydroelectronic control unit receives information about the vehicle speed, direction of travel and road conditions from the wheel speed sensors

Based on this information, the control unit determines the optimal wheel braking mode, changing the flow area of ​​the circuits with the help of solenoid valves, anticipating the blocking moment of the wheel slowing down the rotation, which prevents it from blocking.

If the system assumes blocking any wheel, it instructs the corresponding valve to isolate the fluid supply to the working cylinder of this wheel from the main brake cylinder.

If the wheel speed continues to decrease compared to the other wheels, the ABS system returns the brake fluid back to the master cylinder, relieving braking.

If all four wheels decelerate equally, the return pump will shut off and all solenoid valves will reopen, allowing the master cylinder to act on the slave cylinders as normal. This cycle can be repeated up to ten times per second.

The activation of the solenoid valves and the return pump creates pulsations in the hydraulic drive of the brake system, they are transmitted to the brake pedal, thereby signaling the driver that the ABS is working.

The solenoid valves in the front wheel brake circuits act on their working cylinders independently, on each separately, while the solenoid valve on the rear wheel brake circuits acts on both working cylinders of the mechanisms simultaneously.

Since the braking system is diagonally split, a separate mechanical plunger valve in the hydraulic block divides the hydraulic output of the rear solenoid valve into two separate circuits. to prevent the system from being affected by false signals, an integrated safety loop monitors all signals to the control unit.

If a false signal is received or the voltage in the on-board power supply is insufficient, the system is automatically turned off, and the ABS shutdown warning lamp in the instrument cluster comes on.

In this case, the normal operation of the braking system remains, however, when driving on a slippery road, you need to be extremely careful, since the distribution function of the system will be violated (the function of equalizing the pressure in the braking mechanisms of the front and rear wheels) and there is a possibility of the car skidding when braking.

Parking brake drive - manual, mechanical, cable, to the rear wheels. It consists of a lever, a front cable with an adjusting nut at its tip, an equalizer, two rear cables and levers in the rear wheel brakes.

The parking brake lever, fixed between the front seats on the floor tunnel, is connected to the front cable.

An equalizer is attached to the rear end of the front cable, into the holes of which the front ends of the rear cables are inserted.

The rear ends of the cables are connected to the parking brake actuator levers attached to the rear shoes.

During operation (until the rear brake pads are completely worn out), adjustment of the parking brake drive is not required, because lengthening the brake spacer bar compensates for pad wear.

The parking brake actuator must only be adjusted when the cables or the parking brake lever are replaced.

The working stroke of the brake pedal with the engine running should be approximately 60-65 mm.

Too small stroke indicates an incorrect initial setting of the brake pedal, a maladjustment of the vacuum brake booster, or a seized working cylinder, which leads to increased fuel consumption and accelerated wear of the brake pads.

Too large a working 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 travel is reduced by repeatedly pressing the pedal, i.e. it becomes "harder" in the air system.

If the full pedal travel begins to increase, the system is leaking.

If the brake pedal always vibrates when braking, the brake discs are most likely warped.

In such a situation, they only need to be changed, and both at once.

Periodically appearing and disappearing vibration of the pedal during heavy braking accompanies the operation of the anti-lock braking system and is not a sign of a malfunction.

If, when braking, the car starts to pull to the side, check the working cylinders; they may need to be replaced.

If a knock appears in the front suspension that disappears during braking, check the tightening of the caliper mounting bolts.

Before starting the movement after replacing the brake pads, be sure to press the brake pedal several times - the pistons in the working cylinders must snap into place.

Possible malfunctions of the brake system and methods of correction

Cause of malfunction - Remedy

Extended brake pedal travel:

Leaking brake fluid from the working brake cylinders - Replace defective working brake cylinders,

rinse and dry pads, discs and drums

Air in the brake system - Remove air by bleeding the system

Damaged rubber o-rings in the master cylinder - Replace the master cylinder

Damaged rubber hoses for hydraulic brakes - Replace hoses and bleed the system.

Increased runout of the brake disc (more than 0.03 mm) - Grind or replace the disc if the thickness of the brake discs is less than 19.8 mm

Insufficient braking performance:

Oiled brake pads - Rinse and dry the pads

Seizure of pistons in the working cylinders - Eliminate the causes of seizure, replace damaged parts

Complete wear of the brake pads - Replace the brake pads

Overheated brakes - Stop immediately and allow brakes to cool

The use of low-quality pads - Use original pads or products of firms specializing in the production of parts of brake systems

Leakage of one of the circuits (accompanied by a failure of the brake pedal) - Replace damaged parts, bleed the system

Brake pedal misalignment - Determine the cause of the increase in full travel and replace the damaged parts

Violation of the adjustment of the protrusion of the rod of the vacuum brake booster - Contact the service to adjust the booster

Anti-lock braking system (ABS) malfunction - Contact service to have the anti-lock braking system checked

Incomplete release of all wheels:

There is no free play of the brake pedal - Replace the brake master cylinder

Increased protrusion of the vacuum brake booster rod - Contact service to adjust the booster

Swelling of the master cylinder rubber seals due to the ingress of gasoline, mineral oils, etc. into the liquid. - Flush and bleed the entire hydraulic drive system, replace rubber parts

Seized master cylinder pistons - Check and replace master cylinder if necessary

Braking of one wheel when the pedal is released:

Break or loosening of the return springs of the parking brake pads - Replace the spring

Piston sticking in slave cylinder due to contamination or corrosion of housing - Replace slave cylinder and bleed hydraulic brake system

Swelling of the O-rings of the slave cylinder due to the ingress of impurities into the fluid - Replace the slave cylinder and bleed the hydraulic brake

Incorrect position of the caliper relative to the brake disc when loosening the mounting bolts - Tighten the mounting bolts, replace damaged parts if necessary

Incorrect adjustment of the parking brake system - Adjust the parking brake system

Anti-lock braking system malfunction - Call a service to have the anti-lock braking system checked

Skidding or drifting to the side when braking:

Seizure of the slave cylinder piston - Check and remove the seizure of the piston in the cylinder

Any tube blockage due to dented or obstructed - Replace or clean tube

Dirty or oily discs, drums and brake pads - Clean the brake parts

Wheel alignment wrong - Adjust wheel alignment

Different tire pressures - Set the required tire pressure

One of the brake circuits does not work (accompanied by a decrease in braking performance) - Replace damaged parts and bleed the system. If this does not lead to the desired result, contact the service to check the anti-lock braking system (if it is installed on the car)

Increased effort on the brake pedal when braking:

Vacuum booster defective - Replace booster

The hose connecting the vacuum booster and the intake pipe of the engine is damaged or loose - Replace the hose

Swelling of rubber cylinder seals due to gasoline, mineral oils, etc. - Replace cylinders, flush and bleed the system

Squeak or vibration of brakes:

Grease the friction linings - Clean the linings with a wire brush using warm water and detergent. Eliminate the causes of fluid or grease on the brake pads

Pads worn or foreign inclusions - Replace pads

Excessive runout or uneven wear (felt by vibration of the brake pedal) of the brake disc - Grind or replace the disc if the front brake discs are less than 10.6 mm thick on vehicles with K7J and K7M engines, vehicles with K4M engines less than 17.7 mm

Checking the brakes

It is advisable to check the operation of the brake system on special brake testers.

A rough assessment of the braking system operation can be performed on a flat horizontal platform (preferably covered with a thin layer of sand), buried for traffic.

This check can be done on vehicles without ABS. With ABS, the check is carried out at the workshop using diagnostics.

After braking the car, get out of the car and inspect the brake marks left by the car's wheels.

Особенности тормозов автомобиля Рено Сандеро

If the brake tracks of the front wheels are slightly longer than the rear wheels, and the length of the tracks on the left and right are the same, then the braking system is in good order. If not, repair the system.

The following relationships must be respected:

- L lion. per. = L right. per.

- L lion. rear = L right. rear

- L lane. > L rear

If, when checking a vehicle equipped with ABS, the brake marks are as clearly visible as when checking a vehicle without ABS, then the anti-lock braking system is defective. In this case, you need to contact the service station for ABS repair.