Skoda Felicia

since 1994 release

Repair and operation of the car

The Main Brake Cylinder (MBC) with pressure valves regulators which are built in in it

GTTs is intended for creation of pressure of working liquid in hydraulic contours of the brake system of the car. The cylinder fastens by means of two nuts of M10 on hairpins of the servo-driver of the vacuum amplifier.

GTTs from the case executed from iron casting in which the opening of the cylinder with a diameter of 22 mm in which pistons (3) and (10) of the drive of two contours of the brake system are placed is pierced. In the GTTs horizontal plane four openings with a female thread are executed. Two left openings with a carving of M6x1.5 are intended for a vvorachivaniye of valves regulators of pressure in a contour of brake mechanisms of back wheels. The right openings (M10x1.0) serve for connection of hydraulic lines of contours of forward brake mechanisms. The nests equipped with rubber sealing plugs (5) and (12) through passage under landing of tanks of brake fluid are provided in the top part of the GTTs case.

Back section GTTs is connected to brake mechanisms right forward and left back wheels (the first hydraulic contour). A lobby - to mechanisms left forward and right back wheels (the second contour).

(3) drives of the first brake contour are provided deepening under landing of a tip of a rod of a pusher of the vacuum amplifier of brakes in the piston.

Sealing cuffs (7) and (14) serve for sealing of working spaces of the corresponding sections GTTs. The cuff (9) prevents penetration of hydraulic liquid from one section in another, and a cuff (2) - hit in the air cylinder.

Spring (8) and (15), established under pistons, provide reverse motion of the last. The spring (8), besides, Serves for increase in the effort enclosed to the piston of the second section during braking.

Pins (4) and (11) limit return of pistons.

When squeezing a pedal of a foot brake the movement of a pusher of the servo-driver of the vacuum amplifier of brakes is transferred to the piston (3) GTTs and moves it in the cylinder. At shift the piston squeezes a spring (8) which, together with the increased pressure of hydraulic liquid, displaces the piston (10). The cuffs put on pistons (7) and (14) at the same time are displaced out of limits of inlet openings of tanks of brake fluid. As a result, pressure increases in both hydraulic contours of system.

Rise in pressure in GTTs causes stronger pressing of sponges of sealing cuffs to walls of cylinders, in addition increasing tightness of assembly.

At a pedal otpuskaniye pistons come back to a starting position under the influence of the efforts developed by springs. The inlet openings which are reported with cavities of cylinders open and the hydraulic liquid which is in tanks freely gets to cylinders, automatically compensating the increase path volume connected with wear of frictional slips and/or leaks in lines.

In case of the damage of system causing depressurization of the first hydraulic contour, the piston (3) will freely move as increase of pressure in a working cavity of this section will stop. The piston (10) under the influence of the effort developed by a pusher of the vacuum amplifier and a spring (8) at the increased course of a pedal of a foot brake will provide correct functioning of the second hydraulic contour. In case of violation of tightness of the second contour the piston (10) under the influence of the effort developed by a pusher and a spring (8), overcoming resistance of a spring (15), will move against the stop the core to a face wall of the cylinder. In the first brake contour there will be a normal increase pressure at the increased course of a brake pedal.

The valve regulator(s) limits increase in pressure contours of brake mechanisms of back wheels, preventing premature blocking of the last. The case of the valve is screwed in the GTTs outlet. Tightness of a joint is provided with sealing laying (4). The transitional nozzle providing a possibility of connection to assembly of the brake line is screwed in the outlet of the case of the valve regulator. Brake fluid, coming to an inlet opening of the regulator, passes in a cavity between the rubber valve (3) and the Internal wall of the case. Further liquid gets in the channel provided in the piston (7) and further - to the brake line of a hydraulic contour of the brake mechanism of the corresponding back wheel. The spring (6) is picked up for effort of compression so that with ^{a pressure of liquid up to 20 kgfs/cm of 2} remained on removal from the valve. At further increase of pressure the spring finally contracts and the piston nestles on the valve which blocks an opening through internally in it. As soon as pressure in front of the piston exceeds at a sufficient size pressure behind the piston, the last moves again, opening access of liquid to a contour. Further the cycle is repeated necessary number of times in the course of braking of the car.

Thanks to such functioning of valves regulators pressure in supports brake mechanisms of forward wheels always remains not lower, than in wheel cylinders of mechanisms back that excludes a possibility of a skid of the last.

Pressure valve regulator located near the back bridge

On release models since December, 1995 one valve regulator of pressure in contours of brake mechanisms of back wheels of the car is installed. The design of this regulator is similar that for the valves regulators used on the VW Golf cars.


The regulator corrects pressure in hydraulic contours of brake mechanisms of back wheels of the car depending on loading and the provision of a body.

During performing procedures of routine maintenance of the car it is necessary to pay attention to tightness of connections of the valve regulator and to check freedom of movement of components of its drive. In case of detection of defects the regulator is subject to replacement assembled. Check of serviceability of functioning of the valve regulator has to be made in the conditions of car repair shop.

Tank of brake fluid

The two-chamber tank of brake fluid is made of translucent plastic that allows to control visually liquid level in it. Connecting branch pipes of the tank are inserted into the entrance nests of GTTs equipped with sealing plugs through passage.

Inside the tank is divided by a partition into two independent cameras. The partition does not reach the top cover of the tank that allows to add liquid in both cameras at once. Division of contours happens only after lowering of level of liquid below edge of a partition.

The jellied mouth of the tank is closed by a screw cover in which, along with system of channels of connection of an internal cavity with the atmosphere, plugs of the sensor switch of level of brake fluid and actually the sensor switch are built in (see the Head Onboard electric equipment).

On the case of the tank there are tags of the minimum and maximum levels of liquid.

Vacuum amplifier of brakes

This device is intended for increase in the effort made by the driver for a pedal of a foot brake for the purpose of increase in efficiency of braking.

The case of the block of the servo-driver of the vacuum amplifier consists of two parts: actually cases (5) and covers (1). Tightness of both parts of assembly is provided with landing of the edges of a diaphragm (3) clamped in a case flute. The diaphragm is hermetically put by the central part in a flute of the piston (2) and divides internal space of assembly into two cameras. The spring (10) provides return of a rod (7) together with a diaphragm in a starting position.

The piston is mechanically connected to a rod of a pusher (7). On the end of a rod will screw an adjusting tip (8) by means of which correction of an adjusting gap between the GTTs piston and a pusher is made (see the Section Removal, check of a state and installation of the control valve of the vacuum amplifier of brakes with a hose).

Tightness of landing of a pusher in assembly is provided with rubber laying (6).

In the piston of assembly the valve (12) against which the spherical end of the operating pusher rests (15) is placed. The pusher is connected about a pedal of a foot brake.

In a forward part of the valve (12) there is a saddle of a special form blocked, in turn, by the valve (13). The forward (vacuum) camera (4) is connected by the channel (17) with the piston to the back (atmospheric) camera (11) located behind the piston.

The filter (16), duplicating a role of a rubber protective cover (14), prevents hit of dust in assembly at suction of atmospheric air.

When squeezing a pedal of a foot brake the operating pusher moves the first valve of the piston which locks the channel connecting the vacuum chamber to atmospheric and opens access to the last of external air. Depression in the vacuum chamber at the working engine is created thanks to existence of connection with the inlet pipeline. Owing to difference of pressure from the different parties of the piston the last is displaced to the left, squeezing a spring and resting a pusher rod against the GTTs piston.

At strong squeezing of a pedal of a foot brake the piston of the vacuum amplifier is displaced to the left on considerable distance. At the same time the volume of the atmospheric camera increases a little and in a cavity external air podsasyvatsya.

After a pedal otpuskaniye the valve (4) provides alignment of pressure on both sides of the piston, and the spring returns a diaphragm in an initial state, causing also return shift of a rod of a pusher and, respectively, the first GTTs piston.

Depression giving the forward camera of the servo-driver is carried out via the unilateral valve which is switched on in the line connecting the block to the inlet pipeline of the engine. The valve prevents hit in the vacuum chamber of the servo-driver of air and fuel evaporations at the killed engine. Thanks to this valve the first braking at the decayed engine happens to the working vacuum amplifier (after a pedal otpuskaniye the vacuum amplifier ceases to function).

As appears from the description of the principle of functioning of the servo-driver given above, strengthening of brakes becomes possible only at the working engine when in the inlet pipeline of the last depression is supported.

For a stop towed or moving a setup at the decayed car engine to a pedal of a foot brake it is necessary to put a little bigger, than habitual effort.

Spare parts to the servo-driver of the vacuum amplifier of brakes are not delivered, and therefore, in case of refusal, the block is subject to replacement assembled. The description of procedures of removal and installation of assembly of the servo-driver is provided in the Section Check of Serviceability of Functioning, removal and installation of the vacuum amplifier of brakes. The landing sizes of the block are shown on an illustration.

Brake mechanisms of forward wheels

The main components of the brake mechanism of a forward wheel are the brake disk and assembly of a support with brake shoes.

The brake disk is cast from gray cast iron and fastens to a wheel nave flange one bolt of M6x14. The inside of a disk is protected dirt hits by a special casing.

In the main case a support of the brake mechanism the piston is located. Two blocks equipped with frictional slips are inserted into an anchor bracket.

The case of a support fastens to an anchor bracket by means of one (mechanisms of an original complete set Girgling) or two bolts (mechanisms of license assembly). Anyway bolts are rolled in openings in end faces of the directing fingers. The case at the same time can freely move along the directing fingers.

The directing fingers of a support are covered with a thin layer of silicone lubricant and protected from dirt hit by rubber boots. In an anchor bracket seats under installation of brake shoes and two openings in a carving under bolts by means of which all assembly fastens to a rotary fist of stupichny assembly of a wheel are equipped.

In the case of a support the hydraulic cylinder is concluded with the piston. Tightness of landing of the piston in the cylinder is provided with a sealing cuff.

Blocks consist of a metal plate on which on the one hand the frictional slip is pasted. The block is kept in a saddle by the spring fixed on a plate. In parallel the spring serves for elimination of vibrations of a block.

When squeezing a pedal of a foot brake hydraulic liquid influences the support piston, causing pressing of blocks to a working surface of a disk. Lead movement of the piston to deformation of a cuff. After a pedal otpuskaniye pressure of brake fluid falls and, thanks to spring properties of a cuff, the piston moves back, coming back to the cylinder. The moment when the piston after an otpuskaniye of a pedal ceases to be involved in the cylinder can be caused by wear of cuffs. At the same time blocks will remain pressed to a brake disk and the mechanism begins to overheat.

It should be noted that in process of operation of frictional overlays of blocks the piston gradually starts from the cylinder more and more. At the same time the case of a support is displaced on the directing fingers, automatically compensating wear.

Brake mechanisms of back wheels

The design of the drum brake mechanism of back wheels is presented on illustrations.

The stamped steel brake board fastens to the lever of a suspension bracket of a back wheel. To the lower part of a board of a priklepana arms of brake boots.

Boots have tavrovy section and rest the top end against pushers of pistons of the wheel cylinder, and lower - against the arm fixed on a brake board. On the convex party of boots special glue pasted frictional slips.

Back boots of the right and left brake mechanisms have an identical design whereas lobbies are not interchangeable in view of existence in the lower part of asymmetrically located axes under installation of clamps of automatic correction of working gaps.

Boots are connected among themselves by two coupling springs - top and lower. Springs have different length and provide a prileganiye of the ends of boots both to pushers of pistons of the wheel cylinder, and to axes.

Through an opening in the central part of boots the anchor pin fixed by the forelock is passed. The pin fixes a boot in an axial naprvleniye of rather brake board.

The wheel cylinder) is cast from cast iron. The cylinder a landing flange fastens on a board of the brake mechanism by means of two bolts of M6x10. The opening under the pumping gate is also provided in a flange.

In the cylinder two pistons equipped with rubber sealing cuffs are put. The internal spring provides a constant clip of pushers of pistons to boots of the brake mechanism. Pushers of pistons have the special form and are put on by the groove provided in an external end face the upper edges of boots. The wheel cylinder on both sides is protected by the rubber boots preventing hit of pollution in assembly.

The brake drum is cast from cast iron. In a forward wall of a drum there are ten openings (apart from central). Two openings are intended for fastening of a drum to a flange of stupichny assembly by means of M8x16 bolts, four - for fastening to assembly of a rim, two more are auxiliary and are used at removal of a drum and remained two provide access for check of reverse motion of the lever of the automatic regulator of gaps between boots and a drum.

When squeezing a pedal of a foot brake the brake fluid which is in the wheel cylinder forces to be moved apart assemblies of pistons whose pushers move apart the upper edges of boots, pressing the last frictional slips to the working surface of the reel. After a pedal otpuskaniye boots come back to a starting position thanks to the effort developed by coupling springs.

The excessive size of a gap between boots and the working surface of the reel leads to increase in a free wheeling of a pedal of a foot brake and, respectively to a delay of operation of brake mechanisms. In view of told, the mentioned gap has to be minimized. For this purpose brake mechanisms are equipped with the device of automatic correction of a gap thanks to which the under control distance is constantly supported within 0.4 ÷ 0.6 mm.

The Razzhimny level is a component of the mechanism of the automatic regulator of gaps. Are among other components of the device the clamp established in the lower part of a forward boot with a helicoid spring, and also the spring tense between a level and a special opening in a back boot.

Gap size between frictional overlays of boots and the working surface of the reel depends on gap size between teeths on the lower part of the adjusting lever and teeths on the top part of a clamp.