Brake malfunctions (VAZ-2101)

We have introduced you to brakes, their structure and operating principle earlier, where we described brake maintenance. However, during operation, situations arise when prompt intervention is required. Few people will decide to continue the journey if the brakes are faulty, so we will address them again, but we will consider only the main faults and how to eliminate them.

Insufficient braking efficiency

Fully functional brakes ensure: smooth and simultaneous braking of all four wheels, braking distance that does not exceed the norm, normal temperature of brake drums and wheel disks. When at least one of these conditions is violated, the most urgent intervention is required.

First of all, it is necessary to check the condition of all pipelines, and if dents are found on them, remember that this is dangerous. Even more seriously, you need to take rubber hoses, on the outer shells of which there should not be even the slightest cracks. There should be no dangling tubes, since loosening of the fastening leads to vibrations and subsequent breakdowns.

If braking efficiency has decreased, the driver, no matter how inexperienced, will feel what has happened. The brake pedal will start to spring (will become soft), and to stop the car abruptly, you will have to apply significant force to the pedal. A decrease in braking efficiency is usually caused by the following circumstances.



1. Leakage of brake fluid from the wheel cylinders of the front and rear brakes.

2. Air penetration into the hydraulic drive system.

In both cases, it is necessary to first determine where the liquid is leaking from and where the air is being sucked in, and then decide how to eliminate the defect.

If the tubes are intact, the nipples and plugs are tightened, and drops of brake fluid hang over and over again, the wheel cylinders (leaking) have to be removed, disassembled, the cause of the leak determined and eliminated. As is known, the wheel cylinders of the front brakes are located in the calipers. It is more convenient to remove the caliper and then disassemble it into parts. To remove the caliper (Fig. 65) (without brake disc), you need to disconnect the supply hose and unscrew the two bolts securing it on the outside of the brake shield. To prevent brake fluid leakage, plug the hole in the hose and the rest of the tube with plugs.



To disassemble caliper 4 and get to the wheel cylinder parts, do the following:

• remove the cotter pins 7 of the brake shoe fastening pins;
• remove pins 9 with springs 11;
• remove springs 8 and brake pads 10; disconnect tube 5 and remove dust caps 2 from cylinders;
• using a pump or compressed air hose, supply air to the cylinder through the brake fluid inlet;
• remove the pistons 1 and sealing rings 3 pushed out of the cylinder;
• unscrew the air release valve 6.

All parts should be washed with warm water and dried with a jet of compressed air. Wear marks and scratches on the piston and cylinder mirror are a reminder that the parts need to be replaced. The dust cap and sealing ring are also subject to replacement, and it is advisable to replace these parts with new ones in any case if the piston is removed.


The front brake assembly is performed in the reverse order of disassembly. Before assembly, lubricate the piston, cylinder and sealing ring with brake fluid. After installing the caliper in place and adding brake fluid to the reservoir of the front brake master cylinder, bleed the hydraulic system, i.e. remove the air that has entered the system. This operation is very similar to bleeding the hydraulic clutch drive. It is necessary to bleed the hydraulic system of all four wheels. When starting to bleed the hydraulic system, as well as during the operation, it is necessary to check the presence of brake fluid in the reservoir and not allow its level to decrease, since air can again enter the system and energy will be wasted.

If the culprit of the leak is one of the rear wheel brake cylinders, it is removed and the same operations are performed as with the front wheel cylinders.

The sequence of disassembling the rear wheel brake cylinder (Fig. 66) is as follows: remove the protective caps 1 and pistons 2; remove cuffs 4; support cups 6 with spring; unscrew the air release valve 3. Before assembly, it is necessary to generously lubricate all parts with brake fluid and, without applying any force, install the parts into the cylinder body 5. After installing the protective caps, it is necessary to manually check the smoothness of the piston movement.



3. Damage to the sealing rings (cuffs) 9 of the main brake cylinders (Fig. 67). The cuffs are usually changed, but to do this it is necessary to remove and disassemble the main cylinder.



Remove the master brake cylinder in the following sequence:

• the flexible hoses are disconnected from the main brake cylinder, and the holes in the hoses and fittings are closed with plugs to prevent fluid from leaking out in vain and dirt and dust from getting into the cylinder;
• disconnect the steel tubes through which the brake fluid flows from the master cylinder to the wheel;
• remove the master cylinder, having first unscrewed the two nuts that secure it to the body (for VAZ-2101 and VAZ-2102 cars) or to the vacuum booster (for all other car models).

To disassemble the master cylinder, you must first prepare a comfortable work area: a clean table, good lighting, a tray with brake fluid. Disassembly begins with removing the lock washer 2, nipple 3 with sealing washer 4. Then remove cap 5. All parts of the master cylinder are held in housing 1 by bolt 6. After unscrewing it, take out all the parts: springs 7 and 8; spacer rings 10, pistons 11, cups 12.

In this case, the master cylinder had to be disassembled in order to replace the sealing rings (cuffs) 9, however, having the opportunity to carefully examine each part of the cylinder, pay special attention to the condition of the pistons and the cylinder mirror. They should not have any scratches, unevenness, traces of corrosion, there should not be an increased gap between the piston and the cylinder.

Before assembly, it is advisable to wash the master cylinder parts in isopropyl alcohol and blow them with compressed air (the time the parts are in alcohol should not exceed 20 seconds). When installing the part in place, it is necessary to lubricate it generously with brake fluid.

4. Contamination or oiling of brake drums and shoes. Shoes and drums usually become dirty when driving on wet and dirty roads. They become oily due to excessive lubrication with deformed seals or leakage of brake fluid from the wheel cylinders of the rear wheels. In both cases, the drums must be removed, the sources of oiling eliminated, and the brake shoes and drum mirror wiped with gasoline.

Uneven braking, skidding or pulling away of the vehicle

This defect occurs for various reasons. There are some that are easy to fix. That's where you should start. First of all, you need to check the air pressure in the tires and, if necessary, make it the same on the right and left. At the same time, you should inspect the condition of the treads of all four wheels. Uneven pressure and wear of the treads can cause the car to skid or pull away. Then you need to carefully inspect the hydraulic brake lines. Deep dents on them can prevent the brake fluid from flowing freely to one of the wheel cylinders, causing the car to skid when braking.

A brake failure on at least one wheel will cause non-simultaneous braking and, as a result, the car will drift away from the straight-line direction of movement. This is especially dangerous in winter conditions on a slippery road. There is an old method for checking non-simultaneous braking. The car is placed on a lift or stands, the engine is started and direct (fourth) gear is engaged. At medium engine crankshaft speeds, the brake pedal is smoothly pressed.

If the wheel brakes are in good condition, the engine will stall at the same time as the wheels stop. If the brake on one of the wheels is faulty, the drive wheels will rotate at different speeds. Having discovered such a discrepancy, they find out what the cause is: whether it is incorrect brake adjustment, or a brake fluid leak, or oiling or contamination of the pad linings.

When the simplest causes have been eliminated or ruled out, but the malfunction remains, it is necessary to conduct more in-depth investigations, i.e. check whether the installation angles of the front wheels are not disturbed and whether the pressure regulator is installed correctly. It is advisable to perform these operations at a service station.

Squealing and screeching of brakes

Probably everyone has encountered this defect. An intersection, a red traffic light and various sounds of squeals of stopping cars. VAZ cars, as a rule, stop without noise, but it happens that one of them suddenly squeals at the moment of braking.

Research shows that brake squealing and squeaking occurs when:

• the brake shoe tension spring of the rear wheel brakes has weakened. Such a spring is replaced;
• the brake pads are worn out or heavily contaminated. The pads are cleaned or replaced;
• there is ovality of the brake drums or strong beating of the brake disc, which can be eliminated at a service station (ream the drum or grind the disk). At home, both the disc and the drum are replaced.

Increased effort when pressing the brake pedal

This malfunction usually affects cars equipped with a hydraulic brake booster (Fig. 68). When the booster is in good working order, very little force is required on the brake pedal, and when you press it, you can hear the noise of air entering the booster. If you have to press the pedal hard to brake, then the hydraulic brake booster needs repair. First of all, you need to check the tightness of its components, the condition of the air filter, the serviceability of the valves, the condition of the cylinder, etc.



It is not difficult to disassemble the hydraulic vacuum booster, but we do not recommend doing this, since spare parts for it are not available for sale. At home, you can eliminate the leak (if the hoses are "to blame" or the fastening is loose) and clogged air filter 6.

When the air filter gets clogged, air stops flowing into cavity A and, therefore, the hydraulic vacuum booster is inactive. To get to the air filter, it is necessary to disconnect the pusher 5 from the pedal and remove the protective cover 3 with the clip 4. In case of all other malfunctions, the booster must be removed. To do this, remember the following: when removing the booster, do not disconnect the master cylinder of the brake drive. This will prevent air from entering the system and subsequent bleeding of the brakes.

The operation of removing the amplifier should be performed in the following order:

• disconnect pusher 5 from the brake pedal;
• disconnect the nuts securing the master cylinder to the booster and disconnect the master cylinder;
• loosen the clamps and disconnect hose 2 from tip 1 and the fitting on the engine exhaust pipe;
• unscrew the nuts securing the booster to the clutch and brake pedal bracket and remove the booster from the vehicle.

You have to apply additional force to the brake pedal even when (on all car models) rubber parts in brake cylinders swell. This can happen (this was discussed above), if gasoline, kerosene or mineral oil gets into the brake fluid. There is only one way out of this situation: the cylinders should be disassembled, the rubber parts should be replaced, all parts should be washed in isopropyl alcohol or brake fluid. Naturally, the brake fluid should be drained from the system, the system should be filled with fresh fluid, and it should be bled, removing air.

Incomplete release of braking of all wheels

After driving several dozen kilometers, stop and touch the wheel disks and brake drums. It is not uncommon for drums and disks to heat up to over 60°C. This is the first sign of incomplete release of the wheels. In other words, when the pedal is fully released, the wheels are still under the action of the brakes.

This malfunction can and does occur for the following reasons.

1. There is no free travel of the brake pedal. Only normal (3-5 mm) free travel of the pedal provides the required clearance between the pusher and the piston of the master cylinder, which is necessary for complete release of the wheels.

2. On vehicles equipped with a hydraulic booster, the hydraulic booster adjusting bolt protrudes relative to the mounting plane of the master cylinder. The adjustment is performed according to the diagram: disconnect the master cylinder from the hydraulic booster and check the amount of bolt protrusion. The bolt should protrude relative to the mounting plane of the master cylinder flange by 1.25_-0,2 mm (see fig. 68). If the size does not match, hold the end of the rod and loosen or tighten the bolt.

3. The hydraulic booster valve body is jammed due to swelling of the diaphragm or pinching of the cover seal or protective cap. The defect is eliminated by replacing the hydraulic booster.

4. The master cylinder sealing rings swell or the master cylinder piston seizes. In both cases, the master cylinder is disassembled and the failed parts are replaced.

Braking of one of the wheels with the pedal released

It is easy to determine which wheel is slowing down by the degree of its heating. What is the reason? There may be several:

• the rear brake shoe tension spring has weakened or broken. To more easily identify the fault, you need to hang up the wheels and turn each of them. If there is noise or knocking, then the tension spring is to blame. Remove the drum, change the spring and free the drum from dirt;
• the wheel cylinder piston is seizing; wheel cylinder sealing rings swell;
• the position of the caliper relative to the brake disc is disturbed due to loosening of the bolts;
• there is no gap between the pads and the brake drum.

All these faults are completely fixable, and the process of performing operations is described above.