9.10.12. Repair of brake mechanisms of back wheels

Before performance of repair operations brake mechanisms have to be washed carefully out by warm water with detergents and are dried by compressed air.
It is necessary for dismantling of the brake mechanism of a back wheel:
- to execute operations on removal of brake shoes (see. "Replacement of blocks of brake mechanisms of back wheels");

Fig. 8.16. Removal of a persistent ring




- to disconnect the pipeline from the wheel cylinder, to remove the wheel cylinder and to sort it. For this purpose it is necessary to take off at first rubber protective caps and polyurethane foam rings. Then to turn the screw-driver pistons on 90 ° and to take out them from the cylinder. Spring persistent rings without need should not be deleted. If for any reasons the ring needs to be removed, then special kruglogubets (fig. 8.16) are for this purpose applied. Having entered round sponges (diameter of sponges of 4 mm and height of 5 mm) of the tool into two special openings on a ring, to squeeze kruglogubets and to take out at first one, and then second ring from the cylinder. To turn out the valve of pumping of the wheel cylinder.
To wash out all details warm water with detergents and to dry a stream of compressed air, and then to perform inspection of details of brake mechanisms.
The brake drum on a working surface should not have deep рисок and zadir. If necessary the drum should be chiseled assembled with a nave of rather external rings of bearings. The beating of a working surface of the reel has to be no more than 0,2 mm. Not to reduce drum durability, boring of its internal diameter more than 283,0+0,2 mm is not allowed.
At damage or especially deep risks, and also in need of boring of a working surface of the reel to diameter more than 283 mm it needs to be replaced new.
Brake slips are pasted by VS-YuT glue. Before gluing of a surface of a rim of a block and internal surfaces of a slip it is necessary to smooth out and blow carefully compressed air. Put a uniform layer of glue and let's it dry out during 1 h at a temperature of the production room. Then in special adaptation of a slip to press to blocks with effort 500 — 800 kPa (5 — 8 kgfs/cm2). To put adaptation in the furnace, where to sustain at a temperature of 175 — 185 °C not less than 30 min. without time of warming up of the furnace and blocks up to the specified temperature, then to cool adaptation together with the furnace to ambient temperature during 3 h, not less.
After a prikleyka the external surface of slips is ground so that radius was 0,1 — 0,3 mm less than drum radius that accelerates to extra earnings of blocks.
Blocks with slips which have big wear or are greasy in the course of work, it is necessary to replace new. It is allowed to use for further operation of a block with partially greasy slips. At the same time slips need to be washed out unleaded gasoline, to dry and clear a steel brush or a skin.
It is not necessary to replace only one of blocks of a brake or block of one brake mechanism. It is necessary to make replacement of blocks on both brake mechanisms to exclude withdrawal of the car when braking.
It is necessary to check whether openings of fastening of a board and wheel cylinders are broken. The board should not be bent. Cracks on a board are not allowed.
To wash out the wheel cylinder and details entering it in isopropyl alcohol or pure brake fluid. To clear a mirror of the cylinder a pure napkin. The working surface has to be absolutely smooth, without рисок and roughnesses. To eliminate defects with grinding in. If the piston of the wheel cylinder has teases, became covered by corrosion which cannot be removed without violation of the main metal, or has unilateral wear, it should be replaced new.
If sealing rubber rings of wheel cylinders got out of an initial shape or have defects on a working surface, they also should be replaced new.
Protective covers of wheel cylinders should be changed in the presence of the slightest damages as a result of which tightness is broken. Hit of moisture under protective covers leads to formation of corrosion on the surface of the cylinder and on the piston that can cause jamming of the piston or premature wear of sealing rings.
Assembly of brake mechanisms is made as it should be, the return to dismantling. At the same time it is necessary:
- before assembly of a detail of wheel cylinders to wash out in soda solution, to blow compressed air and to ship in fresh brake fluid;

Fig. 8.17. The provision of persistent rings in cylinders


- to check an arrangement of a cut of a persistent ring of automatic adjustment which has to be in the vertical plane. Depth "And" (fig. 8.17) of installation of a persistent ring in the wheel cylinder has to correspond to 11+0,5 mm;
- to watch that at assembly on sealing rings mineral oil, kerosene and lubricant did not get. Rings should not be overwound.
After assembly of brake mechanisms of back wheels it is necessary to add brake fluid and to pump over system as it is stated above. The sizes of the interfaced details and knots of the brake system are specified in tab. 8.2.

Table 8.2. The sizes of the interfaced details and knots of the brake system, mm