9.10.8. Repair of the main brake cylinder

Wear or loss of elasticity of cuffs, wear of working surfaces of the cylinder and pistons, swelling of cuffs from hit in system of mineral oils, a contamination of compensation openings are causes of defect of the main brake cylinder.

Fig. 8.3. Main brake cylinder: 1 — the case; 2 — a tube; 3 — the connecting plug; 4 — a tank; 5 — a protective cap; 6 — the sensor of a signaling device of emergency falling of level of brake fluid; 7 — a persistent ring; 8 — an external cuff; 9 — the directing plug; 10, 17 — pistons; 11 — a lock ring; 12 — a sealing ring; 13 — a piston washer; 14, 16 — cuffs; 15, 18 — persistent washers; 19 — a spring: 20 — a stopper; And, In — compensation openings; With — perepuskny openings

If liquid level in a tank of the main brake cylinder decreased, and at survey of connections of pipelines and knots, including brake mechanisms, the leak of brake fluid is not found, then in this case leak of brake fluid is possible through an external cuff 8 (see fig. 8.3) in a cavity of A1 of the vacuum amplifier.
If the brake pedal at application of effort to it of about 200 — 300 N (20 — 30 kgfs) at first moves approximately to a half of the course, and then under invariable effort will gradually move to a cab floor, then in this case the main cuffs 14 or dividing 16 are damaged. Defects of dividing cuffs can be found, for this purpose it is necessary from a tank to merge liquid lower than the level of a dividing partition on 10 — 15 mm in each section. If after pressing a pedal of a brake of 3 — 5 times liquid level in sections changes, then it indicates a liquid overflowing from one section in another that is possible only at wear of dividing cuffs.
In case of swelling of cuffs there is, as a rule, a system not disinhibition because of overlapping by the main cuffs of 14 compensation openings. For definition of this malfunction it is enough to disconnect tubes from the main cylinder. If after a liquid effluence from working cavities leak stops and level in a tank does not decrease, then compensation openings are blocked by cuffs or got littered. In these cases the main cylinder should be removed from the car and to sort.
Removal and dismantling of the main brake cylinder need to be carried out in the following order:
- to clear of dirt the main brake cylinder, the vacuum amplifier and pipelines attached to the main cylinder;
- to disconnect pipelines from the main brake cylinder and to muffle them rubber caps from pumping valves;
- having turned off two nuts, to remove the main brake cylinder from hairpins of a cover of the vacuum amplifier;
- to uncover 6 a tank and to merge brake fluid;
- to turn the cylinder a tank down and, having pressed several times the piston 10, to remove the remains of brake fluid from the main cylinder;
- to disconnect a tank from the main brake cylinder and to take from the cylinder case connecting rubber plugs 3 with tubes 2;
- to turn off a stopper 20, to take a spring 19 with a persistent washer 18. To press the piston 10 then the piston 17 with cuffs 14 and 16 can be taken a hand;
- to remove a lock ring 11 nippers 7814-5593 or special flat-nose pliers;

Fig. 8.10. Primary piston of the main cylinder: 1 — a spring; 2 — the holder of a spring; 3 — the screw; 4 — a persistent washer; 5 — a cuff; 6 — a washer; 7 — the piston

- to take a hand for a shaft the piston 10 assembled. To remove from the piston the directing plug 9, an external cuff 8 and a persistent ring 7. It is not recommended without need to unscrew the screw 3 (fig. 8.10) of the holder.
After dismantling it is necessary to examine attentively details of the main brake cylinder and to be convinced that the mirror of the cylinder and the working surfaces of pistons absolutely pure and on them is absent a rust, risks and other defects. At the defects causing considerable change of internal diameter of the cylinder or at its unilateral wear to replace the case new.
Rubber cuffs are recommended to be replaced new at each dismantling of the main brake cylinder. Before assembly of the main brake cylinder to wash out all details in alcohol or pure brake fluid. Not to allow hit of mineral oils, gasoline, kerosene or diesel fuel on a detail as at the same time rubber cuffs can be damaged.
It is necessary for assembly of the main brake cylinder:

Fig. 8.11. Installation of cuffs of the main brake cylinder: 1 — the main cuff; 2 — dividing cuffs; 3 — an external cuff

- to install cuffs on pistons, as shown in fig. 8.11;
- to grease a cylinder mirror with brake fluid;
- to assemble primary piston 6 (see fig. 8.10), to check the size of (19±0,275) mm it (is not regulated);
- to grease a cuff 14 (see fig. 8.3) with fresh brake fluid and to insert the piston 10 into the case of the main cylinder;
- to insert a persistent ring 7, the external cuff 8 directing the plug 9 and a lock ring 11, using nippers or flat-nose pliers;
- to install on the piston 17 dividing cuffs 16, a washer of the 13th piston, the main cuff 14, a persistent washer 18 and a spring 19;
- to grease cuffs with fresh brake fluid and to insert the piston into the cylinder case;
- overcoming resistance of a spring 19, to wrap a stopper 20 with laying;
- to install connecting plugs 3 with tubes 2 in the cylinder case, previously having greased them with fresh brake fluid;
- to install a tank 4 on connecting plugs 3;
- to install the main brake cylinder on the vacuum amplifier, previously having checked a condition of a sealing ring 12, and if necessary to replace it;
- to fill in brake fluid in a tank and to pump over system as it is stated above.

Before installation in the main brake cylinder of new details from the last it is necessary to remove carefully conservation lubricant to exclude hit it in the brake system.