The principle of operation and malfunctions of the master brake cylinder

If the brake cylinders fail, depending on the type of defect, the rear wheels may lock when released or, conversely, continue to rotate freely when the brake pedal is pressed. In any case, you shouldn’t wait for this moment, especially since replacing the rear brake cylinders can easily be done with your own hands.

Classification of car brake systems

Modern cars are equipped with three or four types of brake systems:

The main and most effective braking system of a car is a working one. It is used throughout the movement to regulate speed and come to a complete stop. Its device is quite simple. It is activated by pressing the brake pedal with the driver's right foot. This procedure ensures simultaneous reduction of engine speed, by removing the foot from the accelerator pedal, and braking.

The parking brake system, as the name suggests, is designed to keep the vehicle stationary during long periods of parking. In practice, experienced drivers leave the car in first or reverse gear. However, on large slopes this may not be enough. » alt=»»> The manual parking brake is also used when starting off on uneven sections of the road, when the right foot should be on the gas pedal and the left foot presses the clutch. By smoothly releasing the brake lever with your hand, simultaneously engaging the clutch and adding gas, you can prevent the car from arbitrarily rolling downhill.

The auxiliary braking system is installed on heavy-duty vehicles, for example, on domestic KamAZ, MAZ, KrAZ vehicles. It is designed to reduce the load on the main working system during prolonged braking - when driving in the mountains or on hilly terrain.

System design and principle of operation

The main thing in the braking system of any car is the brake mechanisms and their drives. The hydraulic brake drive used on passenger cars consists of:

1. pedals in the cabin;
2. working brake cylinders of front and rear wheels;
3. vacuum booster;
4. pipeline (brake pipes);
5. master brake cylinder with reservoir.

The principle of operation is as follows: the driver presses the brake pedal, driving the piston of the brake master cylinder. The piston squeezes fluid into the pipelines to the brake mechanisms, which in one way or another create resistance to the rotation of the wheels, and thus braking occurs.

When the brake pedal is released, the piston returns via a return spring, and the fluid flows back into the master cylinder - the wheels are released.

On domestic rear-wheel drive cars, the brake system design provides for a separate supply of fluid from the master cylinder to the front and rear wheels.

On foreign cars and front-wheel drive VAZs, the pipeline circuit diagram “left front – right rear” and “right front – left rear” is used.

Checking after replacing the fuel pump

As soon as the new part is installed, you need to check its functionality. The brake pads are checked (whether they are separated at the place where the brake parts are replaced), as well as the system itself for leaks. Experienced motorists check even before installing the wheel, but this requires an assistant. However, there is no way to bleed the brake system yourself.

Check after replacing the rear brake cylinder

Check the rear brake cylinder as follows:

• the assistant sits in the driver’s seat and, pressing the brake pedal, fixes it in this position;
• the second diagnostic participant turns the brake drum with his hands;
• the same second participant looks to see if there are any traces of liquid;
• If there are no leaks, the wheel is installed in its place.

Checking the brake system after repair

On a note! If, when the brake is pressed, the drum rotates or traces of fluid appear, this indicates a faulty brake cylinder. Even if the part is new, it must be replaced.

Types of brake mechanisms used in cars

The vast majority of cars are equipped with friction-type brake mechanisms that operate on the principle of friction forces. They are installed directly in the wheel and are structurally divided into:

There was a tradition of installing drum mechanisms on the rear wheels and disc mechanisms on the front. Today, depending on the model, the same types can be installed on all four wheels - either drums or discs.

Design and operation of the drum brake mechanism

The drum-type system device (drum mechanism) consists of two shoes, a brake cylinder and a tension spring located on a shield inside the brake drum. Friction linings are riveted or glued onto the pads.

Replacing a faulty brake cylinder

The replacement scheme in the VAZ family is almost the same for cylinders of both circuits with minor differences.

Initially, you need to prepare the necessary keys and plugs suitable for the size of the pipes. After removing the wheel and unscrewing the pipes, we put plugs on them to prevent fluid leakage. Having unscrewed the corresponding nuts, we dismantle the old cylinder and put a new one in its place, reassembling it in the reverse order. If, after replacement, wheel assembly is hindered by pads that are too far apart, you can file the ends of the pads, just don’t overdo it, as this may affect the operation of the handbrake.

After any manipulations with the brake system, it must be bled according to the diagram.

Comparative characteristics

Drum brakes are simpler and cheaper to manufacture. They have a property called the mechanical self-reinforcement effect. That is, with prolonged pressure on the pedal with your foot, the braking effect increases many times over. This occurs due to the fact that the lower parts of the pads are connected to each other, and the friction of the front pad on the drum increases the pressure of the rear pad on it.

However, the disc brake mechanism is smaller and lighter. Temperature resistance is higher, they cool faster and better due to the provided window openings. And replacing worn disc pads is much easier than replacing drum pads, which is important if you carry out the repairs yourself.

Servicing brake discs and pads

Wear and replacement of discs

Brake disc wear is directly related to the driver's driving style. The degree of wear is determined not only by mileage, but also by driving on bad roads. Also, the degree of wear of brake discs is affected by their quality.

The minimum allowable thickness of a brake disc depends on the make and model of the vehicle.

The average value of the minimum permissible thickness of the front brake disc is 22-25 mm, rear – 7-10 mm. It depends on the weight and power of the car.

The main factors indicating that the front or rear brake discs need to be replaced are:

• disc beating when braking;
• mechanical damage;
• increase in braking distance;
• decrease in the level of working fluid.

Wear and replacement of pads

Brake pad wear primarily depends on the quality of the friction material. Driving style also plays an important role. The more intense the braking, the greater the wear.

The front pads wear out faster than the rear ones due to the fact that they experience the main load during braking. When replacing pads, it is better to change them at the same time on both wheels, be it rear or front.

Pads installed on one axle can also wear unevenly. This depends on the health of the working cylinders. If the latter are faulty, then they compress the pads unevenly. A difference in the thickness of the linings of 1.5-2 mm may indicate uneven wear of the pads.

There are several ways to determine whether your brake pads need to be replaced:

1. Visual, based on checking the thickness of the friction lining. Wear is indicated by a lining thickness of 2-3 mm.
2. Mechanical, in which the pads are equipped with special metal plates. As the linings wear out, the latter begin to come into contact with the brake discs, which causes disc brakes to squeak. The reason for squeaking brakes is abrasion of the lining up to 2-2.5 mm.
3. Electronic, which uses pads with a wear sensor. As soon as the friction lining wears down to the sensor, its core comes into contact with the brake disc, the electrical circuit is closed and the indicator on the dashboard lights up.

Working principle of the parking brake

It is a purely mechanical device. It is activated by raising the handbrake lever to a vertical position until the latch clicks. In this case, tension occurs on two metal cables running under the bottom of the car, which tightly press the brake pads of the rear wheels to the drums.

To release the car from the parking brake, press the locking button with your finger and lower the lever down to its original position.

Car brake system care

As one of the most important components, the car's braking system requires constant attention and care. Here, literally any malfunction can lead to unpredictable consequences on the road.

Some diagnoses can be made based on the behavior of the brake pedal. Thus, an increased stroke or a “soft” pedal most likely indicates that air has entered the hydraulic drive system as a result of a brake fluid leak. Therefore, it is necessary to periodically monitor the liquid level in the tank.

Its increased consumption may be a consequence of damage to hydraulic hoses and tubes, as well as ordinary evaporation over time. This causes air to enter the system and cause brake failure.

Parts that have become unusable must be replaced, and the system will have to be pumped by bleeding air from each working cylinder on the wheels and adding fluid. The process is long and tedious. » alt=»»> If the car pulls to the side when braking, it indicates a possible failure of one of the working cylinders or excessive wear of the linings on a particular wheel. If the brake mechanisms are dirty, a characteristic noise may occur when you press the pedal.

All these malfunctions can be easily fixed independently or by contacting a service center. And to minimize the troubles described above, take care of your brakes and use engine braking more often, especially on steep and long descents. Prolonged activation of the main working system leads to overheating of parts and causes various breakdowns.

One of the main systems that ensures safety when driving a car is the braking system. The most widespread are brake mechanisms that use the frictional force of different materials. Such mechanisms are installed on all cars, including VAZs belonging to the “Classic” family.

As an example of a classic VAZ, model 2107 will be used. The brake system of the VAZ-2107 includes working and parking systems. The task of the working component is to reduce the speed of movement of the car until it is completely immobilized.

It consists of two components: the first is the brake mechanisms, which act on the wheels, which is why their rotation decreases. The second component is the drive, through which the driver operates the mechanisms.

The parking component ensures that the wheels of one of the car's axles are locked, in the case of the VAZ-2107 - the rear axles, while the car is immobilized. The use of this brake prevents spontaneous movement of the car. This system uses a separate drive that acts on the rear axle mechanisms.

In more detail, what the brake system of the VAZ-2107 looks like is shown in the diagram:

Now let's take a closer look at the design of the VAZ-2107 brake system. First, let's go through the working component. Its drive is hydraulic and includes:

• Control pedal;
• Vacuum booster;
• Main cylinder;
• Tank for working fluid;
• High pressure pipelines;
• Rear axle bellows pressure regulator;

The use of liquid as a working element of the drive is due to a number of positive qualities: a complex system of levers for the drive is not required, the wiring of pipelines to the mechanisms is facilitated, the transmission of force from the driver’s foot is enhanced several times due to the vacuum booster.

The working mechanisms on the VAZ-2107 are of two types: disc brakes are installed at the front, using calipers; drum-type mechanisms are used on the rear axle, which also includes a parking mechanism.

Now in more detail about the elements of this system. So, the pedal that the driver presses is located on the same axis as the clutch control pedal. To ensure that it can be returned to its original position, it is spring-loaded.

Symptoms of problems

The general technical condition of the car (including the brake system) can be checked using a personal diagnostic adapter - a car scanner. These types of devices are widespread and have a wide price range. We would like to draw your attention to the budget model of Korean production Scan Tool Pro Black Edition.

At a cost of about 2 thousand rubles. This scanner is capable of fully diagnosing your car (engine, gearbox, transmission, abs, srs and much more), which will pay for itself in 1-2 trips to the service station. The adapter is quite easy to use, has Russian-language software and is compatible with most cars produced in 1993. The device will also be useful when buying a used car, as it can show its real mileage and VIN.

The fluid brake system consists of many parts that can become unusable: pipes, wheel cylinders, calipers, drums and pads. Typical signs of a faulty master cylinder:

1. After pressing the pedal, the car stops slowly. The reason is that the cuffs of one or two pistons have lost their tightness - they have cracked or “floated”.
2. To slow down, you need to press the brake pedal hard. The phenomenon occurs due to swelling of the rubber of the piston seals.
3. The brake pedal travel is too short. The fluid inside the cylinder has nowhere to go because the compensation hole is clogged. Another option is that the passage is blocked by a swollen rubber seal.
4. A common symptom is pedal failure, the brakes coming on at the end of the stroke. This indicates complete wear of the cuffs; as a result, liquid penetrates behind the piston and rushes into the expansion tank - the cylinder “bypasses.”
5. The pads do not release the brake discs and drums and get very hot when driving. Options: one of the pistons is jammed or the bypass hole is clogged.

The listed symptoms of a GTZ malfunction are similar to malfunctions of other elements. Pedal failure also occurs when a large amount of air enters the tubes or loss of fluid in one of the working cylinders. Sluggish deceleration and increased force on the pedal are often caused by a breakdown of the vacuum booster - a cracked membrane or a lack of tightness at the joints of the hose that takes off engine vacuum.

There are signs that clearly indicate the performance of the main hydraulic cylinder and the malfunction of other elements:

• during braking, the car pulls to the side - the problem lies in a certain circuit or wheel;
• jamming of the brake mechanisms of one wheel;
• creaking and squeaking when braking;
• heating the discs and pads on one wheel.

If you eliminate these symptoms, it will become easier to check the brake master cylinder in a garage. This also includes obvious brake fluid leaks and the knocking sound of worn calipers.

There are other symptoms indicating a malfunction of the gas turbine engine.

• When braking at speed, the car pulls to the side. This happens when one of the circuits or brake cylinders on the wheel is faulty.
• The appearance of a squeaking or knocking noise during braking. It could also be pads that are time to be replaced, but it happens that the problem is in the GTZ.
• The pads can jam, heat up and heat up the brake disc on a particular wheel.

Vacuum brake booster

A rod connected to the amplifier is connected to the pedal. The design of the VAZ-2107 vacuum brake booster is quite interesting; it is shown in the figure:

The amplifier is a sealed container, internally divided into 2 chambers by means of a membrane. The chamber located closer to the pedal is called atmospheric, and the chamber separated from it by a membrane is called vacuum. The diaphragm itself is connected to the piston rod of the master cylinder.

The vacuum chamber is connected by a pipe to the intake manifold of the engine, where the vacuum comes from. The design also includes a follower valve controlled by the pedal rod, which does all the work.

When the pedal is released, this valve connects the chamber cavities through a channel, providing identical pressure. When the pedal is applied, the valve closes the channel connecting the chambers and opens the channel connecting the atmospheric chamber with the atmosphere. Since a vacuum is maintained in the second chamber, atmospheric pressure begins to put pressure on the membrane. Since it is connected to the piston rod of the master cylinder, due to the movement of the piston, fluid is displaced from the cylinder into the pipelines.

Caliper device

Let's move on. The front axle mechanisms are disk ones, consisting of calipers with the main brake elements - pads, and brake discs.

A caliper is a body with cylinders made in it for the pistons. This model has two of them, one for each block. The support structure is shown in the figure.

The caliper pistons have the form of a glass, which is placed in their cylinders, but they can move along it. To prevent fluid leakage, the pistons are equipped with o-rings.

Pads are small metal plates onto which linings made of friction material are glued.

The brake disc is made of metal for better adhesion to the surface of the pads; its side surfaces are well processed so that there are no protrusions or shells on them.

The VAZ 2107 brakes work like this: the fluid moves into the caliper cylinders, where it begins to push out the pistons. They come out of the cylinders, pressing the pads against the disc.

Rear axle brake mechanism

The brake system of the VAZ-2107 rear axle has a different device. All its elements are hidden inside the brake drum:

The working brake cylinder of the VAZ 2107 has the following device: there is a body, also known as a cylinder, with two pistons placed in it. When exposed to fluid pressure, they come out of the cylinder.

The pads are metal, made in the shape of crescents, with friction clutches glued to their upper edge. The pads installed on the hub form a ring.

In the lower part, the pads are installed in the seats made under them, and in the upper part - in the grooves made in the pistons. To prevent the pads from moving apart spontaneously, they are tightened with springs. The parking brake mechanism is also located there.

On top of all this there is a drum mounted on the hub shaft. When braking, the fluid pushes the pistons, and since the pads fit into their grooves, this movement of the pistons is accompanied by the divergence of the pads. At the same time, they are pressed towards the drum and the rotation slows down.

Checking the brake master cylinder

The design of the brake master cylinder involves the use of rubber sealing parts, which periodically fail and become the main problem during testing. Therefore, if the brake system has problems described above, it is necessary to check its operation. And you need to start with the GTZ. The check is performed in the following sequence:

• It is necessary to check for drips on the body, as well as for cracks on it.
• Next, you need to check the tightness and condition of the cylinder sealing elements. For any amount of repair work carried out, it is necessary to replace all rubber seals that are included in the repair kit for the main brake cylinder.

If the check shows changes in the operation of the gas turbine engine, then without waiting for it to completely fail, we recommend repairing it by replacing some elements from the repair kit. Please note that it can only be used to fix minor problems (for example, brake fluid leaks).

If the cylinder mirror is damaged , that is, scratches, cavities or other damage appears on it, then it becomes unrepairable. The only way out in this case is to completely replace it.

Source

Parking system

Although it engages the mechanism of the rear axle wheels, it is in no way connected with the working mechanism. It uses a cable as a drive connected to the handbrake located inside the car.

Under the car, this cable is divided into two parts, going into the rear axle mechanisms. Inside, the ends of the cable are connected to the drive lever, which in turn is connected to a spacer bar. The drive lever is connected to one of the pads.

When the handbrake is engaged, the cable pulls the lever, and since it rests against the bar, the pads are released. The toothed sector of the handbrake fixes the position of the lever when the pads are spread apart.

Pressure regulator

It is installed in the rear wheel drive and not only distributes fluid to the mechanisms, it also prevents possible skidding due to different forces on the mechanisms. This is done by limiting the supply of pressure to the mechanisms, depending on the position of the car body relative to the bridge.

The regulator is driven by a rod, one end of which is fixed to the rear axle, while it itself is fixed to the body. As the load on the rear axle increases, the body changes position relative to the axle; as a result, the rod puts pressure on the regulator piston, which adjusts the pressure supplied to the mechanisms.

The principle of operation of the VAZ-2107 brake system

If it is necessary to reduce speed, the driver presses the pedal. Its force is transmitted to the amplifier valve, which opens the required channel to supply atmospheric pressure to the membrane. The membrane is connected to a rod connected to the piston of the main cylinder. This rod displaces fluid into the pipelines leading to the operating mechanisms. Since the liquid is not compressed, all force is completely transferred to the mechanisms.

The liquid presses on the pistons of the working cylinders, and as they move out, they unclench (on drum bellows) or press the pads (on disk bellows) to the disk or drum connected to the wheel hubs. Due to the friction of the pads on the discs (drums), the rotation slows down.

Causes of malfunction in the GTZ device

If there is a leak in one of the circuits, the pressure between the primary and secondary cylinders is lost. This leads to the fact that the GTZ functions as if it had only one circuit. The pusher will begin to move both pistons in the good circuit until the piston of the faulty one reaches the end of the cylinder body. Accordingly, the required pressure will be ensured in the depressurized chamber. If the idle mechanism is properly adjusted, the vehicle will effectively slow down the vehicle even in conditions of its inferiority.

Here are some signs of a malfunction in the GTZ device:

• depressurization of the cylinder is determined by the presence of a leak in the body and a specific smell;
• brake pad wear is characterized by a characteristic squeak and leakage of brake fluid;
• jamming of the regulator, which distributes the brake force. In this case, it is necessary to clean the cylinder body. There is a low threshold of sensitivity of the brake pedal; it has to be literally “sunk” into the floor;
• the pedal falls to the floor - this damage occurs due to non-working pistons. If they are not able to generate the required pressure, then the pads cannot compress normally;
• An increase in the brake pedal travel is a sign that the vehicle has become airy. Operating a car in this condition is dangerous, since there is a high risk of overheating the vehicle to the point of boiling. Pumping will help eliminate this problem.

If any of the above happens constantly, we can talk about damage to the vacuum booster valve or a complete loss of tightness in the system. If the metal housing itself is damaged or there are scuffs on the piston, a complete replacement of the turbocharger is required. When the gasket wears out, all components of the repair kit (sealing collars, rubber gaskets, springs) are changed.

How to bleed the master brake cylinder? You need to unscrew the air release valve in the cylinder body and press the pedal until a perfectly uniform liquid flows out, without any air. Upon completion, the valve returns to its place and the reservoir must be refilled with liquid. The sequence of bleeding the mechanisms is as follows: 1 - rear right; 2 — front left; 3 — rear left; 4 - front right.

A common cause of malfunction of this element is loss of housing tightness and leakage of brake fluid. The defect that causes brake fluid leakage is a rear cuff leak, which can be determined by the presence of oil at the junction of the turbocharger and the vacuum booster. This may occur due to the breakdown of flexible tubes due to friction with the rotating wheel.

It’s good if, in the area where the highway passes through the arch, it is protected by a special spring that prevents the wheel from rubbing the element. If the fluid level is low, you need to check the tightness of the entire vehicle and replace the damaged tube.

Types of maintenance work

Despite the fact that the system is not so complicated structurally, it requires periodic maintenance, including:

• Checking the fluid level in the system;
• Checking the degree of wear of friction clutches, pads, discs, drums;
• Bleeding the system to remove air;
• Checking the condition of the handbrake cables;
• Adjustment of cable tension;
• Adjusting the rear brake adjuster;

Before each trip, you must always check how much brake fluid is in the VAZ-2107 system. An insufficient amount of it can lead to the fact that the efficiency of the system can be significantly reduced due to air getting inside the pipelines. In addition, a decrease in level may indicate damage to pipelines and fluid leakage.

The elements of the mechanism should be checked every few months, this is especially true for the pads, since they wear out quite intensively. If necessary, worn elements are replaced.

If air gets inside the drive of the working system, pumping is performed, as a result of which the air is expelled from the system.

Loosening the tension of the parking brake cables can lead to its failure, so you need to periodically monitor it and, if necessary, restore the tension.

Possible faults

During operation, the master brake cylinder, like all vehicle mechanisms, becomes unusable, which entails repair or replacement of parts. The main reason may be uneven distribution of brake fluid inside the structure. Diagnosis of malfunctions is carried out first using an external inspection: checking for defects and brake fluid leaks. Then they check the functionality of the unit: with normal pressure on the rod, there should be no jamming or sagging.

Features of the braking system

One of the features of the VAZ-2107 brake circuit is the presence of a dual-circuit system. The essence of a dual-circuit system is that the working drive is divided into two parts, each of which supplies fluid to only two mechanisms, while the circuits do not interact with each other.

The presence of two circuits ensures the operability of the brakes of at least two wheels in the event of depressurization of one of the circuits. That is, even if the pipelines of one circuit are punctured, the second will remain fully operational, which will ensure the functioning of the brakes.

In the VAZ-2107, the circuits are divided in such a way that the drive of the front axle mechanisms is separated from the drive of the rear mechanisms. This allows you not only to maintain the functionality of the system when one of the circuits fails, but also to pump each circuit separately. That is, if one of the circuits is airy, then it needs to be pumped, but it is not necessary to service the second one.

This is only general information about how the VAZ-2107 brake system works, and does not include all the details on its maintenance and repair. In general, the brakes of this car work quite well, although some elements of it cause complaints from car owners.

What is needed for replacement

To replace the brake cylinder, you need to take care of preparing some tools and materials:

• set of wrenches;
• screwdriver;
• pliers;
• dry rags;
• metal brush;
• WD-40 (if things don't go according to plan);
• jack;
• brake cylinder;
• balloon wrench.

Tools for replacing the rear brake cylinder
Before replacing, it is advisable to purchase a set of brake pads, since they still need to be changed periodically, and the disassembled rear of the car will allow you to do this without any problems. The work needs to be done in a spacious room or outside, so that there is somewhere to put the spare parts after dismantling. It is important to remember not only the sequence of their removal, but also the method of removal . Once everything is ready, you can begin repair work.

Brake cylinder puller