Renault Logan is equipped with two independent brake systems: working and parking
The first, equipped with a hydraulic drive with a vacuum booster and an anti-lock system (installed on request), provides braking when the car is moving, the second slows down the car in the parking lot
Two-circuit working system 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 to stop the car with sufficient efficiency.
The hydraulic drive includes a vacuum booster and a dual-circuit rear brake pressure regulator.
The parking brake system has a cable drive to the rear wheel brakes.
The brake mechanism of the front wheel, disc, with automatic adjustment of the gap between the pads 2 (Fig. 1.) and disc 1, with a floating caliper.
The movable bracket is formed by a caliper 3 with a single-piston working cylinder.
The 4 shoe guide is bolted to the steering knuckle.
The movable bracket is bolted to the guide pins 5, installed in the holes of the guide shoe.
The guide pins are lubricated with grease and protected with rubber boots.
A piston with a sealing ring is installed in the cavity of the wheel cylinder.
3a due to the elasticity of this ring, the optimal clearance between the pads and the disc is maintained, 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 releasing the piston, due to the elasticity of the sealing ring, it is removed from the pad, a small gap forms between the pads and the disc.
Rear wheel brake - drum, with a two-piston wheel cylinder and two brake shoes, with automatic adjustment of the gap between the shoes and the drum.
The brake drum is also the hub of the rear wheel and the bearing is pressed into it.
Pressure regulator changes the pressure in the hydraulic drive of the rear wheel brakes depending on the load on the rear axle of the car.
It is included in both circuits of the brake system, through it the brake fluid flows to both rear brake mechanisms.
The regulator is bolted to the car body.
Its rod is connected to the rear suspension beam through a spring-loaded load rod, lever 4 and an earring.
Depending on the distance between the beam and the body, which depends on the vehicle load, the regulator rod moves, which, in turn, with the help of a valve system, 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 brake mechanisms of the rear wheels are the same.
The front pads of the brake mechanisms of the rear wheels are the same, while the rear ones are different - they are mirror-symmetrically equipped with non-removable parking brake levers.
The spacer bar and ratchet nut of the left and right wheel brakes are different.
The ratchet nut and lug of the left wheel spacer bar are left hand threaded, while the ratchet nut and lug of the right wheel spacer bar are right hand threads.
The levers of the brake mechanisms of the left and right wheels are mirror-symmetrical.
Anti-lock braking system (ABS) consists of a hydro-electronic unit with hydraulic solenoid valves, wheel speed sensors, an electrically driven pump and a warning light in the instrument cluster.
The anti-lock braking system is used to regulate the pressure in the brake mechanisms of all wheels when braking in difficult road conditions, preventing the wheels from blocking.
ABS provides the following benefits:
- — avoiding obstacles with a higher degree of safety, including during emergency braking;
- - shortening of the braking distance in case of an emergency while maintaining directional stability and controllability of the car, including in a turn.
In the event of a system failure, a function is provided to maintain operation in case of system failures.
The hydroelectronic control unit receives information about vehicle speed, direction of travel and road conditions from 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 electromagnetic valves, anticipating the moment of blocking the wheel that slows down rotation, which prevents it from blocking.
If the system expects a wheel to be blocked, it instructs the appropriate valve to isolate the fluid supply to that wheel's slave cylinder from the brake master cylinder.
If a wheel's speed continues to decrease relative to the other wheels, the ABS system returns the brake fluid back to the master cylinder, reducing braking.
If all four wheels decelerate equally, the return pump will shut off and all solenoid valves will open again, allowing the brake master cylinder to act on the slave cylinders normally.
This cycle can repeat 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 to the driver that the ABS is working.
The solenoid valves in the circuits of the brake mechanisms of the front wheels act on their working cylinders independently, on each separately, while the solenoid valve of the circuits of the brake mechanisms of the rear wheels acts on both working cylinders of the mechanisms simultaneously.
Because the braking system is diagonally split, a separate mechanical plunger valve in the hydraulic block separates the hydraulic output of the rear solenoid valve into two separate circuits.
In order to prevent false signals from affecting the system, a built-in safety loop monitors all signals entering the control unit.
If a false signal is received or the voltage in the on-board electrical network is insufficient, the system is automatically turned off, the ABS deactivation warning lamp in the instrument cluster lights up.
In this case, the normal operation of the brake system is maintained, however, when driving on a slippery road, you need to be extremely careful, since the distribution function of the system will be impaired (the function of equalizing the pressure in the brake mechanisms of the front and rear wheels) and there is a possibility of skidding the car when braking.
Parking brake drive - manual, mechanical, cable, on the rear wheels.
It consists of a lever, a front cable with an adjusting nut on 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 cable ends are connected to the parking brake 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. extension of the brake spacer compensates for pad wear.
The parking brake actuator only needs to be adjusted if the cables or the parking brake lever have been replaced.
The stroke of the brake pedal with the engine running should be approximately 60-65 mm.
Too little stroke indicates an incorrect initial setting of the brake pedal, a violation of the adjustment of the vacuum brake booster or a seizure of the working cylinder, causes increased fuel consumption and accelerated wear of the brake pads.
Too much stroke is a sign of excess clearances in the pedal mechanism or a leak in the hydraulic drive of the brake system.
If the stroke decreases when the pedal is pressed repeatedly, i.e. it becomes "harder" in the air system.
If the full pedal travel starts 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.
Pedal vibration that appears and disappears periodically 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.
Before moving After replacing the brake pads, be sure to press the brake pedal several times - the pistons in the working cylinders should fall into place.
Possible malfunctions of the brake system and methods of correction
Cause of malfunction - Remedy
Increased brake pedal stroke
Leakage of brake fluid from working brake cylinders - Replace failed working brake cylinders,
Rinse and dry pads, discs and drums
Air in the brake system. Damaged rubber o-rings in the master cylinder - Bleed the air by bleeding the system. Replace Master Cylinder
The rubber hoses of the hydraulic brakes are damaged. Increased runout of the brake disc (more than 0.03 mm) - Replace the hoses and bleed the system. Grind or replace the disc if the thickness of the braked discs the front of the wheels is less than 19.8 mm
Insufficient braking performance
Oiling the brake pads - Wash and dry the pads
Jamming of pistons in working cylinders - Eliminate the causes of jamming, replace damaged parts
Complete wear of the brake pads - Stop immediately and let the brakes cool down
Brake overheating - Replace brake pads
Use of poor quality pads - Use original pads or products from companies specializing in the production of brake parts
Violation of the tightness of one of the circuits (accompanied by the 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 a Service Center to Check Your Anti-Lock Braking System
Incomplete release of all wheels
No free play on brake pedal - Replace brake master cylinder
Increased protrusion of the vacuum brake booster rod - Contact the service to adjust the booster
Swelling of the rubber seals of the main cylinder due to the ingress of gasoline, mineral oils, etc. into the liquid.
- Flush and bleed the entire hydraulic drive system, replace rubber parts
Jammed master cylinder pistons - Check and replace master cylinder if necessary
Braking one wheel when the pedal is released
Broken or loose parking brake shoe return springs - Replace spring
Piston sticking in the working cylinder due to contamination or corrosion of the body - Replace the working cylinder and bleed the brakes
Swelling of the sealing rings of the working cylinder due to the ingress of impurities into the liquid - Replace the working cylinder and bleed the hydraulic brake system
Violation of the position of the caliper relative to the brake disc when the mounting bolts are loosened - Tighten the mounting bolts, if necessary, replace the damaged parts
Incorrect parking brake adjustment - Adjust the parking brake
Anti-Lock Braking System Abnormality - Have an Anti-Lock Braking System Test
Sliding or pulling the car to the side when braking
Jamming of the piston of the working cylinder - Check and eliminate the jamming of the piston in the cylinder
Clogging of any tube due to dent or blockage - Replace or clean tube
Dirty or oily discs, drums and brake pads - Clean brake parts
Wheels out of alignment - Adjust wheel alignment
Various tire pressure - Set the required tire pressure
One of the brake circuits does not work (accompanied by a decrease in braking efficiency) - Replace damaged parts and bleed the system. If this does not lead to the desired result, contact the service to check the anti-lock brake system (if 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 engine intake pipe is damaged or its fastening is loose - Replace the hose
Swelling of rubber cylinder seals due to the ingress of gasoline, mineral oils, etc. into the liquid. - Replace cylinders, flush and bleed the system
Squeak or vibration of the brakes
Oiling the friction linings - Clean the friction linings with a wire brush using warm water and detergent. Eliminate the causes of fluid or grease on the brake pads
Worn pads or foreign matter 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 brake discs of the front wheels of cars with K7J and K7M engines is less than 10.6 mm, cars with K4M engine is less than 17.7 mm
Checking the brakes
It is advisable to check the operation of the brake system on special brake stands.
An approximate assessment of the operation of the brake system can be performed on a flat horizontal area (preferably covered with a thin layer of sand), buried for traffic.
This test can be carried out on vehicles without ABS. With ABS, the test is carried out at the service station using diagnostics.
After braking the car, get out of the car and inspect the brake marks left by the car's wheels.
If the brake tracks of the front wheels are somewhat longer than the rear wheels, and the length of the tracks on the left and right is the same, then the brake system is working. Otherwise, repair the system.
The following ratios must be respected:
- - L lion. per. = L right. trans.
- - L lion. rear = L right. rear
- - L lane > L rear
If the same check on a car equipped with ABS shows the brake marks as clearly as when checking a car without ABS, then the anti-lock brake system is faulty.
In this case, you need to contact the service station for ABS repair.