Fig. 8.11. The brake mechanism of forward wheels with the ventilated disks: 1 – arm; 2 – support bracket; 3 – the union for pumping with a protective cover; 4 – internal block; 5 – connection of the sensor of wear of blocks

For this operation it is necessary to remove wheels. On forward wheels the ventilated brake disks which thanks to such design well take away heat from friction (fig. 8.11) are established. On back wheels continuous disks are established (without air vents). When checking blocks it is always necessary to examine also brake disks, at least when replacing blocks. Disks with scratches, flutes from wear, besides deterioration in brake characteristics, result in the increased wear of blocks.

SEQUENCE OF WORKS

1. Gray color of a disk is not a malfunction sign.

2. Pay attention to risks and wear tracks on a disk. They appear from dirt or too worn-out blocks. If depth рисок is more than 0,5 mm, replacement of a disk is necessary. The ventilated disks with threadlike scratches up to 25 mm long can be not replaced. However at their increase replacement is required.

3. Check a disk beating — it should not touch blocks at their easy data.

Fig. 8.12. Measurement of thickness of a disk by means of two coins (arrow)

4. Check disk thickness in several places. It is the best of all to measure by a caliper, previously having installed under its sponges on a drive two coins (fig. 8.12) – at a worn-out disk measurements will be more exact. Do not forget to subtract thickness of coins from the received result.

5. Brake disks cannot be processed.

6. Worn-out disks always should be replaced in couple.

The sizes of brake disks for cars with diesel engines are presented in tab. 8.1.

PRACTICAL ADVICE The sizes of brake disks for cars with petrol engines are presented in tab. 8.2.

1. If you open the closed hydraulic system of brakes somewhere, working liquid will follow. It prevents work, and then the dolivka of brake fluid will be required. It is possible to avoid it as follows: before work at first open the union for pumping of the brake mechanism of the corresponding wheel. Press a pedal of a brake and hold it. For this purpose it is possible to use a wooden stick of the corresponding length which should be clamped between a pedal and a driver's seat. Pistons in the main cylinder in this situation block openings of supply of brake fluid therefore it does not follow.

2. At repair of supports or pistons of brake cylinders it is impossible to apply to lubricant oil or other substance at all. Brake fluid should not come into contact with them. Besides, lubricant will become more liquid when heating and can get on the working surfaces of the brake mechanism. Special lubricants which, as a rule, are in a set to spare parts are necessary. At installation of the piston in the brake cylinder, for example, special paste for the brake cylinder is used (from ATE). This substance is also applied on inside of a new protective boot.

3. The brake support which during dismantling was completely exempted from brake fluid can bring certain difficulties during pumping of system. Even by repeated pressing a brake pedal liquid can not come to it. In this case act as follows: after installation of a support do not fix the top end of a brake hose on the pipeline of the brake system. Via the open union for pumping pump brake fluid until it does not begin to follow from the top end of a brake hose. After that fix a brake hose and wrap the union for pumping. After that pump over system. For pumping of brake fluid use the new plastic container filled with brake fluid and connected through a transparent hose to the union for pumping. At the same time it is necessary to lift a container and to pump in the brake mechanism brake fluid without vials of air.

4. Be careful at the treatment of brake fluid. It is aggressive in relation to paint and varnish coverings and is very poisonous. Do not allow its hit in a mouth or on open wounds.

5. The brake fluid merged from system cannot be reused. Do not use liquid from a container which long time was open. The used brake fluid needs to be utilized as appropriate.

6. After works with a hydraulic actuator of brakes check pressure: for this purpose several times strongly press a brake pedal. Then at the working engine once again strongly press a pedal (200–300 N). Pressure in system has to remain, i.e. resistance of a pedal should not decrease.

7. Rubber details of the brake system on which oil got are subject to replacement.

PREVENTION After completion of works several times press a brake pedal for installation of blocks in normal situation. If not to make it, brakes will not work at the first braking. It is necessary that new brake shoes were carefully earned extra. For this purpose weak pressing a pedal several times slow down the car from the speed of 80-40 km/h.