Brake drive

The car is equipped with two types of brake systems - working and parking. The first serves to regulate the speed of the car and stop it with the necessary efficiency, and the parking brake system keeps the car stationary relative to the road.

The service brake system has a hydraulic drive with diagonal separation of circuits, one of which actuates the brake mechanisms of the right front and left rear wheels (pos 84), the other is the left front and right rear wheels (pos 85). Diagonal drive is combined with a negative rolling shoulder of the front wheels (see «Front suspension»). Such a drive scheme ensures the preservation of rectilinear motion and sufficient braking efficiency in case of depressurization of one of the circuits. In this case, the working circuit will act as a backup brake system.

The parking brake system has a mechanical drive to the rear wheel brakes. In addition to its main purpose, the parking brake system can be used as an emergency in case of failure of the MH of one or both circuits of the service brake system.

The hydraulic drive of the working brake system includes a vacuum booster 10 and a pressure regulator 5 of the rear brakes. The amplifier creates comfort when driving by reducing the force on the brake pedal and reducing the pedal travel. The pressure regulator prevents the rear wheels from locking before the front wheels lock. It works at a certain pressure, and its action does not depend on the load on the rear axle of the car, unlike previous VAZ models.


A number of units of the working brake system are unified with other models. So, for example, a vacuum booster is used from a VAZ-2103 car, the main brake cylinder - from VAZ-2121, master cylinder reservoir - from VAZ-21011, front and rear hoses - from VAZ-2108. A number of parts for the brake drive and brake mechanisms have also been unified.

The drive of the working brake system includes: brake pedal 1, vacuum booster 10, master cylinder 8 and its reservoir 9, rear brake pressure regulator 5, wheel cylinders of the brake mechanisms of the front and rear wheels and pipelines of diagonal circuits.

Pedal 5 (see ch. 18) The brake is used to drive the vacuum booster. It, together with the clutch pedal, is suspended from the bracket 1 using the axis 6. The pedal hubs are equipped with two plastic bushings 30 with a diagonal cut through which the axis common to both pedals passes. Pedal bushings are lubricated with Litol-24 grease during assembly, and do not require additional lubrication during vehicle operation. The brake pedal is mounted on the axle between the cheek of the bracket 1 and the spacer sleeve 31. The axle of the pedal in the holes of the bracket is fixed by the locking clip 8.

In the initial position, the brake pedal is set by the return spring 50. In this position, the pedal rests against the plastic stop of the brake light switch 51. The brake pedal is pivotally connected to the pusher 49 of the vacuum booster valve. The connecting pin is fixed in the pusher hole with a locking clip.

Vacuum booster

The vacuum booster is attached to the bracket plate of the clutch and brake pedals on four studs with nuts. A rubber gasket is installed between the vacuum booster and the bracket plate.

Between the case of the vacuum booster and its cover, the outer belt of the rubber diaphragm 40 is clamped, separating the booster into vacuum A and atmospheric B cavities. The vacuum cavity is connected to the engine inlet pipe through a hose with a tip 30 and a valve 31. To seal the connection, the tip 30 is connected to the vacuum booster through the rubber flange 32.

Inside the vacuum booster there is a plastic valve body 39, the shank of which is sealed with a seal 45 at the outlet of the booster body. To protect the movable shank of the valve body from contamination, a corrugated protective cover 47 is put on the flanged part of the cover of the amplifier body and on the shank of the valve body.

A buffer 38, a piston 44 with a pusher 49, a rubber valve 46, springs with support cups and an air filter 48 are placed in the valve body.

The thrust plate 42 enters the groove of the piston 44, the other end of which abuts against the belt of the diaphragm 40, which prevents it from falling out. This plate fixes the piston assembly with the pusher 49 and the valve 46 in the valve body 39. The rod 37 of the master cylinder piston drive rests against the buffer 38. At the outlet of the vacuum booster housing, the rod is crimped with a seal 35, which is pressed by the clip 34 to the seat of the booster housing. A bolt 15 is screwed into the end hole of the rod, which regulates the output of the rod from the amplifier housing (1,25_-0,2 mm) The ball head of the valve lifter is crimped into the piston seat 14.


The rubber valve 46 is assembled on the pusher 49. The movable valve head, reinforced with a metal washer, is pressed by a spring through the support cup to the rear end of the piston (at full disengagement). The body 39 has a seat for the moving valve head. The fixed shoulder of the valve is pressed by a spring through the support cup against the inner wall of the valve body shank, creating a reliable seal. To clean the atmospheric air, a foam air filter 48 is installed in the shank of the valve body. The body 33 and the cover 41 of the amplifier are connected to each other by inserting the protrusions of the cover into the depressions of the body and then turning the cover to plant its edges under the protrusions of the body. The connector of the cover and the body of the amplifier is sealed with a shoulder of a rubber diaphragm 40, sandwiched between them.

In the amplifier housing, a plastic tip 30 is attached through a rubber flange 32, into which a vacuum valve 31 is mounted. It prevents the combustible mixture from entering the vacuum cavity A of the amplifier.

The performance of the vacuum booster can be checked on the car without removing it. To do this, press the brake pedal 5... 6 times with the engine off to create the same pressure in cavities A and B, close to atmospheric. Keeping the brake pedal depressed, start the engine. With a working vacuum booster, the brake pedal after starting the engine should «go ahead».

If the brake pedal is not «goes ahead», check the attachment of the hose tip, the condition and fastening of the tip flange in the amplifier, the hose to the tip and the engine inlet pipe fitting, since loosening or damage to the fastening sharply reduces the vacuum in cavity A and the efficiency of the amplifier.

Master cylinder

The master cylinder is attached to the body of the vacuum booster with a flange on two studs. There are two pistons inside the cylinder: front 23 and rear 16. The front piston serves to drive the circuit «left front - right rear brakes», rear - to drive the circuit «right front - left rear brakes». A plug 24 with a sealing gasket is screwed into the cylinder body from the end. Between the plug and the piston, as well as between both pistons, springs 21 are installed, which return the pistons to their original position. The return stroke of the piston under the action of the springs is limited by screws 17, the shanks of which go into the grooves of the pistons. The groove length of each piston corresponds to their maximum stroke.

O-rings 19 and 29 are located in the rear groove of the piston 16 and in its annular groove. The front part of the piston 16 passes into a shaped shank, which is the guide for the return spring 21. The shank has a central drilling, which is connected to the annular groove through two radial holes. The liquid passing through the central drilling and radial holes exerts pressure on the inner surface of the front sealing ring 19, which ensures a tighter fit of the ring to the cylinder surface.

The front sealing ring 19 is subjected to the force from the spring 20, which tends to press the sealing ring against the end face of the piston groove. The other end of the spring rests against the support cup 28. The spacer sleeve 18 is loosely put on the groove of the piston.

The rear sealing ring of the front piston is pressed against the end surface of the piston by the spring 21 through the support washer 22.

For reliable sealing, the outer diameter of the sealing rings is slightly larger than the inner diameter of the cylinder. The shape of the rings, rounded on the side of the cylinder mirror, provides minimal friction resistance and quite satisfactory lubrication of the sliding surface.

Piston 16 cavity circuit «right front - left rear brakes» in its design differs from the piston 28 of the cavity of the circuit «left front - right rear brakes» the rear part, in which an annular groove is machined to accommodate the low pressure sealing ring 29.

Holes are made in the cylinder body from above. In the bore of two of them, plastic fittings 25 are inserted and fixed with lock washers 26. Gaskets 27 are installed under the flanges of the fittings.

Pipe fittings of both circuits are screwed into the threaded holes.

The hydraulic brake reservoir is made of translucent plastic, which allows you to control the fluid level without removing the reservoir cap. It is attached to the body mudguard strut bracket with a clamp in the engine compartment under the hood.

The lower part of the tank is divided by a partition into two cavities. This provides independent brake fluid supply to each of the two circuits. The filler neck of the tank has a thread onto which the cap 56 is screwed.

On the neck of the tank under the lid there is a plastic case 57 of the contact device with contacts 52 and 53 and a rubber reflector 58, which prevents the penetration of liquid to the contacts.

A pusher 55 passes through the opening of the body 57, at the upper end of which there is a movable contact 53, and at the lower end there is a float 60.

A terminal device body 54 with two terminals for wires is installed on the body of the contact device. When installing the housing, the terminal rivets are pressed against the contacts. The upper end of the pusher 55 comes out through the opening of the housing 54.

The inner cavity of the tank communicates with the atmosphere through the hole in the upper part of the reflector 58, the hole in the housing 54 of the terminal device and, further, through the gaps between the housings of the terminal and contact devices.

When the liquid level drops, the float 60 drops, the movable contact 53 comes into contact with the fixed contact 52, and a lamp with a red light filter lights up on the instrument panel.

To check the serviceability of the liquid level control device in the tank, press the pusher 55. In this case, contacts 52 and 53 close and the control lamp lights up.

Pressure regulator

The pressure regulator 5 of the rear brakes is connected to both circuits of the brake system, and through it the brake fluid flows to both brake mechanisms. It is attached in the engine compartment to the left pillar of the mudguard of the body.

There are four chambers in the pressure regulator: E and B are connected to the master cylinder, D - to the right, and D - to the left wheel cylinders of the rear brakes.

Installed in the pressure regulator housing «floating» bushing 70 with a pusher 71. To separate the cavities E and G, the pusher bushing is sealed on both sides with rubber rings 69. The pusher bushing has a radial hole that can be aligned with the hole in the socket of the pressure regulator housing into which the plug 87 is pressed. there will be fluid leakage, then the o-rings 69 are leaking fluid and should be replaced.

Under the action of spring 67, the pusher bushing, together with the support washer 72, is pressed against the bushing 73, which is fixed in the regulator housing with a retaining ring. The other end of the spring 67 abuts against the plug 63, in which the valve 65 is rolled along with the seat 66. Under the action of the spring 64, the valve 65 is pressed against the end of the annular groove of the pusher shank 71. The valve seat has axial and radial holes through which the cavity E communicates with the cavity D regulator.

On the other hand, the piston head 77 rests against the pusher. It is installed in the sleeve 76, which is sealed from the side of the cavity B by ring 75, and on the other side rests against the retaining ring.

Cavities C and D can communicate with each other through the gap between piston 77 and seal 74 if the piston head moves away from seal 74 under the action of the spring.

Seal 74 and ring 75 are expanded by a spring with support washers until the seals stop against bushings 73 and 76.

The moment of turning on the pressure regulator is determined by the force of the spring 79, which acts on the piston through the stop 78. The other end of the spring, through the support ring 81 and the protective cap 82, abuts against the beaded part of the cup 80. It is fixed on the regulator body by compressing the cup on the groove of the body at six points.

In the initial position of the brake pedal, the parts of the pressure regulator occupy the following position: the piston head 77, under the force of the spring 79, is pressed against the seal 74 and abuts against the pusher 71, moving the valve 65 through it, which moves away from its seat 66. This forms gaps I and G (see ch. 29), through which cameras B and E communicate, respectively, with cameras D and D.

Parking brake drive

The drive of the parking brake system is mechanical, it acts on the brake mechanisms of the rear wheels. It consists of a lever 11 of a manual drive, an adjusting rod 83, an equalizer 13, cables 14, a lever 20 (see ch. 27) shoe drive and expander bar 21, the length of which can be changed manually when adjusting the brake.

The lever 11 of the parking brake is pivotally connected with a finger to the rod 83. The finger is locked with a bracket. At the other end of the rod, an equalizer of 13 cables is fastened with an adjusting nut with a thrust washer. The position of the nut on the rod is fixed with a lock nut.

In the nest, at the ends of the equalizer, the front ends of the rear cables 14 are installed. The rear tips of the cables are connected to the levers of the manual drive of the blocks.

The cable is located in a multilayer sheath having its ends at the ends. The rear tip is installed in the seat of the brake shield, and the front tip enters the seat of the body bracket. In addition, the cable sheath additionally rests on two brackets of the rear suspension arm and the body bracket. Said sheath supports provide free, without jamming, movement of the cable in it, and also protect the cable from damage.

Lever 20 (see ch. 27) of the manual drive of the pads is pivotally connected with a bolt 22 to the rear brake shoe. The bolt is fixed with a nut. The ribs of the block and the lever go into the grooves of the stops of the expansion bar 21. The tip 42 of the cable is put on the lower end of the lever of the manual drive of the blocks. To return the cables to their original position when releasing, springs 40 are installed at their ends.