The Renault Duster car is equipped with two independent braking systems: the service and the parking system.
The first, equipped with a hydraulic drive with a vacuum servo, provides braking while the car is moving, the second brakes the car when parked.
The service system is dual-circuit with a diagonal connection of the brake mechanisms of the front and rear wheels.
One circuit of the hydraulic drive provides the operation of the right front and left rear brake mechanisms, the other — of the left front and right rear.
If one of the circuits of the service brake system fails, the second circuit is used, ensuring the car stops with sufficient efficiency.
A vacuum servo is included in the hydraulic drive.
The car is equipped with an anti-lock braking system (ABS).
A parking brake system with a cable drive on the rear wheel brake mechanisms is installed on the car.
The front wheel brake mechanism is a disc type, with automatic adjustment of the clearance between the pads and the disc, with a floating caliper.
The movable caliper is formed by the caliper with a single-piston wheel cylinder.
The pad guide is secured with bolts to the steering knuckle.
The movable caliper is secured with bolts to the guide pins installed in the openings of the pad guide.
The guide pins are lubricated with consistent grease and protected by rubber covers.
In the cavity of the wheel cylinder a piston with a sealing ring is installed.
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 action of fluid pressure, presses the inner pad against the disc; as a result of reaction forces the caliper moves on the pins and the outer pad is also pressed against the disc, the pressing force of the pads being then identical.
When releasing the brake, the piston, due to the elasticity of the sealing ring, is withdrawn from the pad, and a small clearance forms between the pads and the disc.
The brake mechanisms of the left and right front wheels are not interchangeable.
The inner brake pads are also not interchangeable. They differ in the location of the recesses on the anti-vibration and anti-squeal steel plate.
On the inner pads marks are applied — arrows indicating the direction of rotation of the wheel.
If, when installing, the pads are mixed up, they will squeal when braking.
The master brake cylinder of the "tandem" type of the hydraulic drive of the brakes is installed in the engine compartment directly on the vacuum brake servo.
It 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.
On the master cylinder, through rubber connecting bushes, a reservoir is installed, the inner cavity of which is divided by partitions into three compartments.
Each of the two main compartments feeds one of the chambers of the master brake cylinder, and the third compartment feeds the master cylinder of the clutch release hydraulic drive.
When the brake pedal is pressed, the pistons of the master brake cylinder begin to move, with the working edges of the seals close the compensation holes, the chambers and the reservoir are separated, and the displacement of the brake fluid begins.
In the plug of the reservoir a brake fluid level sensor is installed.
When the fluid level drops below the permissible value, a warning lamp of the faulty state of the brake system lights up in the instrument cluster.
The flange for connection to the vacuum brake servo is sealed with a rubber ring.
The vacuum servo, installed between the pedal mechanism and the master brake cylinder, when braking, due to the vacuum in the engine intake pipe, through the rod and the piston of the first chamber of the master cylinder, creates an additional force proportional to the pedal force.
The hose connecting the vacuum servo to the intake pipe is made in one piece with the check valve, inserted through a rubber bush into the servo body.
The valve retains the vacuum in the servo when it drops in the intake pipe and prevents the fuel-air mixture from entering the vacuum servo.
The rear wheel brake mechanism is a drum type with automatic adjustment of the clearance between the pads and the drum.
The brake pads are actuated by a single hydraulic wheel cylinder with two pistons.
The optimal clearance between the drum and the pads is maintained by a mechanical regulator installed on the expander bar.
As the pad linings wear, the yoke turns the regulator nut and its threaded end piece lengthens, compensating for the increasing clearance between the expander bar and the rib of the front pad.
The rear wheel brake mechanisms of 4x2 and 4x4 cars are practically identical.
The differences relate only to the construction of the brake drums.
On all-wheel-drive cars the brake drum is secured to the hub, while on front-wheel-drive cars the brake drum is itself part of the rear wheel bearing assembly and the bearing is pressed into it.
The automatic clearance adjustment mechanism consists of the composite expander bar of the pads, the regulator lever and its spring.
It begins to work when the clearance between the pads and the brake drum increases.
When the brake pedal is pressed, under the action of the wheel cylinder pistons, the pads begin to diverge and press against the drum, the protrusion of the regulator lever moving along the hollow between the teeth of the ratchet nut.
With a certain wear of the pads and pressing of the brake pedal, the travel of the regulator lever is sufficient to turn the ratchet nut by one tooth, thereby increasing the length of the expander bar and simultaneously reducing the clearance between the pads and the drum.
Thus the gradual lengthening of the expander bar automatically maintains the clearance between the brake drum and the pads.
The wheel cylinders of the rear wheel brake mechanisms are identical.
The front pads of the rear wheel brake mechanisms are identical, while the rear ones differ — on them, mirror-symmetrically, non-removable parking brake drive levers are installed.
The expander bar and the ratchet nut of the left and right wheel brake mechanisms (of a 4x4 car) differ.
On the ratchet nut and on the end piece of the expander bar of the left wheel a right-hand thread is made, and on the ratchet nut and on the end piece of the expander bar of the right wheel — a left-hand thread.
The regulator levers of the left and right wheel brake mechanisms are mirror-symmetrical.
The car is equipped with an anti-lock braking system (ABS).
The fluid from the master brake cylinder enters the ABS unit, and from it is supplied to the brake mechanisms of all wheels.
The ABS unit, secured in the engine compartment on the right side member near the front panel, consists of the hydraulic unit, the modulator, the pump and the control unit.
The ABS acts depending on the signals of the inductive-type wheel speed sensors.
The front wheel speed sensor is located in the wheel hub assembly — inserted into the opening of the steering knuckle.
The encoder disc of the front wheel speed sensor is the protective washer of the hub bearing, located on one of the two end surfaces of the bearing.
This dark-coloured washer is made of magnetic material.
On the other end surface of the bearing an ordinary light-coloured protective washer is located.
The rear wheel speed sensor of a 4x2 car is secured on the brake mechanism backplate, and the encoder disc of the sensor is a ring of magnetic material pressed onto the collar of the brake drum.
The rear wheel speed sensor of a 4x4 car is located in the wheel hub assembly — inserted into the opening of the knuckle.
When braking the car, the ABS control unit determines the beginning of the wheel locking and opens the corresponding solenoid valve of the modulator to discharge the pressure of the working fluid in the channel.
The valve opens and closes several times per second, therefore one can make sure that the ABS is working by the slight trembling of the brake pedal at the moment of braking.
If an ABS fault occurs, the brake system remains operational, but wheel locking is then possible.
In this case the corresponding fault code is written into the memory of the control unit, which is read using special equipment at a service centre.
The parking brake drive is manual, mechanical, cable-operated, on the rear wheels.
It consists of the lever, the front cable with an adjusting nut on its end piece, the equaliser, two rear cables and levers in the rear wheel brake mechanisms.
The parking brake lever, secured between the front seats on the floor tunnel, is connected to the front cable.
To the rear end piece of the front cable the equaliser is attached, in the openings of which the front end pieces of the rear cables are inserted.
The rear end pieces of the cables are connected to the parking brake drive levers secured on the rear pads.
During operation (until complete wear of the rear brake mechanism pads) adjustment of the parking brake drive is not required, since the lengthening of the expander bar of the brake mechanism compensates for the wear of the pads.
The parking brake drive must be adjusted only in the event of replacement of the cables or the parking brake lever.
Possible faults of the brake system and methods of correction
- Cause of the fault — Method of correction
Increased working travel of the brake pedal:
- Leakage of brake fluid from the working brake cylinders — Replace the failed working brake cylinders, wash and dry the pads, discs and drums
- Air in the brake system — Remove the air by bleeding the system
- Damaged rubber sealing rings in the master brake cylinder — Replace the master cylinder
- Damaged rubber hoses of the brake hydraulic drive — Replace the 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 front wheel brake discs is less than 19.8 mm
Insufficient braking efficiency:
- Oil contamination of the pad linings of the brake mechanisms — Wash and dry the pads
- Seizing of the pistons in the wheel cylinders — Eliminate the causes of seizing, replace damaged parts
- Complete wear of the brake pad linings — Replace the brake pads
- Overheating of the brake mechanisms — Stop immediately and let the brake mechanisms cool down
- Use of low-quality pads — Use original pads or products of firms specialising in the manufacture of brake system parts
- Loss of tightness of one of the circuits (accompanied by a drop of the brake pedal) — Replace the damaged parts, bleed the system
- Disturbance of the position of the brake pedal — Determine the cause of the increase of the total travel and replace the damaged parts
- Disturbance of the adjustment of the protrusion of the rod of the vacuum brake servo — Contact the service for adjustment of the servo
- Disturbances in the operation of the anti-lock braking system (ABS) — Contact the service for checking the anti-lock braking system
- Incomplete release of all wheels — Replace the master brake cylinder
- No free travel of the brake pedal
- Increased protrusion of the rod of the vacuum brake servo — Contact the service for adjustment of the servo
- Swelling of the rubber seals of the master cylinder due to the ingress of petrol, mineral oils, etc. into the fluid — Wash and bleed the entire hydraulic drive system, replace the rubber parts
- Seizing of the master cylinder pistons — Check and, if necessary, replace the master cylinder
Braking of one wheel with the pedal released:
- Breakage or weakening of the retracting springs of the parking brake pads — Replace the spring
- Jamming of the piston in the wheel cylinder due to contamination or corrosion of the body — Replace the wheel cylinder and bleed the brake hydraulic drive system
- Swelling of the sealing rings of the wheel cylinder due to the ingress of foreign impurities into the fluid — Replace the wheel cylinder and bleed the brake hydraulic drive
- Disturbance of the position of the caliper relative to the brake disc when the securing bolts are loosened — Tighten the securing bolts, if necessary replace the damaged parts
- Incorrect adjustment of the parking brake system — Adjust the parking brake system
- Disturbances in the operation of the anti-lock braking system — Contact the service for checking the anti-lock braking system
Skidding or pulling of the car to one side when braking:
- Seizing of the wheel cylinder piston — Check and eliminate the jamming of the piston in the cylinder
- Clogging of some pipe due to a dent or contamination — Replace or clean the pipe
- Contamination or oiling of the discs, drums and pad linings — Clean the parts of the brake mechanisms
- Disturbed wheel alignment angles — Adjust the wheel alignment angles
- Different pressure in the tyres — Set the necessary pressure in the tyres
- One of the circuits of the brake system does not work (accompanied by a decrease in braking efficiency) — Replace the damaged parts and bleed the system. If this does not lead to the desired result, contact the service for checking the anti-lock braking system (if it is installed on the car)
Increased effort on the brake pedal when braking:
- Faulty vacuum servo — Replace the servo
- Damaged hose connecting the vacuum servo and the engine intake pipe, or its attachment loosened — Replace the hose
- Swelling of the rubber seals of the cylinders due to the ingress of petrol, mineral oils, etc. into the fluid — Replace the cylinders, wash and bleed the system
Squealing or vibration of the brakes:
- Oil contamination of the friction linings — Clean the linings with a metal brush using warm water with detergents. Eliminate the causes of the ingress of fluid or grease onto the brake pads
- Wear of the linings or foreign inclusions in them — Replace the pads
- Excessive runout or uneven wear (felt by the vibration of the brake pedal) of the brake disc — Grind or replace the disc if the thickness of the front wheel brake discs is less than 19.8 mm
