When the engine is running and the vacuum booster is working, the brake pedal should not reach the floor of the cab during braking - the gap between the pedal and the floor should be at least 40 mm
The performance of the vacuum booster is checked as follows: with the engine off, press the brake pedal 3-4 times, and then, when you press the pedal again, holding it with a force of 300-400 N (30-40 kgf), start the engine.
If the booster is working, the pedal will move slightly towards the floor, and you will hear a hiss of air passing through the booster filter.
If the pedal does not move or it is difficult to move, then the cause is a malfunction of the amplifier or improper adjustment of the engine at idle.
It is also necessary to make sure that the vacuum booster and the non-return valve are sealed. To do this, turn off the engine, hold for 1-2 minutes and press the pedal several times.
During the first three presses, you should hear the sound of air entering the amplifier. If this does not happen, the vacuum booster or check valve is faulty.
Completely disassemble the amplifier only when necessary.
Remove the amplifier from the car and disassemble it in the following order:
Fig. 1. Device for disassembling and assembling the amplifier
- clean the amplifier from dust and dirt, disconnect the rubber hose from the check valve, and the main cylinder from the amplifier;
- fix the main cylinder with a reservoir so that liquid does not spill out of it (this eliminates the pumping of the system after repair);
- remove the cotter pin, unscrew the nut securing the pusher eye axle to the brake pedal and remove the spring washer, axle and plastic bushings;
- unscrew the four nuts securing the vacuum booster to the front panel of the cab, remove the booster from the engine compartment;
- fasten with two nuts on the studs of the cover 6 (Fig. 1) of the body a special plug 5 with a handle for turning the cover and with a tube 2 for connecting a vacuum gauge;
- install the vacuum booster in a special fixture 4, fixed in a vice 8;
- screwing the screw 3 into the device, drown the cover 6 of the vacuum booster until a small gap appears in the connection cover - housing 7;
- insert the extension into the handle of the cap and turn the handle until the protrusions on the body coincide with the slots on the cover. Loosen the screw a few turns and remove cover 6 with spring 21 (see Fig. 2);
- unscrew the piston connector nut and remove piston 5 with diaphragm 7, plate and thrust ring;
- remove the amplifier from the fixture and remove the thrust cover and other parts of the amplifier from the housing, remove the lock washer and remove the pusher from the connector;
- unscrew the three bolts with spring washers and remove the connector, piston 10 with diaphragm 8 and diaphragm 18 with spring.
Remove reaction rubber washer 20 from piston 10; unscrew the two screws 19 fixing the pusher piston 17 in the valve body 15, and remove the pusher with the piston;
- unscrew the pusher lug after loosening the locknut;
- slightly compress the pusher spring, remove the lock washer and remove the rest of the parts from the pusher.
The plunger with the piston is a non-separable connection. Remove the lock washers and remove the guide plastic rings 12, as well as the sealing rubber cuffs 13, from the thrust cover and the body 11 of the amplifier;
- remove the sealing rubber ring from the piston connector;
- remove the non-return valve 1 from the housing cover and replace it if necessary. Clean all parts of the amplifier from dirt and inspect.
Replace parts that are damaged or excessively worn.
Special attention should be paid to checking the rubber parts of the amplifier, as well as the condition of the external polished surfaces of the piston connector and the 15 valve body.
If there are scratches and scuffs, these surfaces should be carefully cleaned with fine sandpaper and washed. If filter 14 is clogged, it must be replaced.
Before assembly, all parts of the amplifier must be absolutely clean. If necessary, all parts, with the exception of rubber, can be washed in clean kerosene and dried with compressed air.
Assemble the amplifier in the reverse order of disassembly.
When assembling, the following features must be taken into account: - the rubber sealing ring in the 15 valve body must be lubricated with greaseoh CIATIM-221;
- after installing the sealing collars 13 in the body and the thrust cover, lubricate their inner surfaces with a thin layer of lubricant CIATIM-221;
- install the assembled pusher with the piston in the body of 15 valves. Lightly press the pusher, overcoming the resistance of the spring, and screw in the two fixing screws 19.
Tighten the screws until they stop, then back them off 0.5 turns each and lock them to prevent loosening.
The pusher with the piston should move without jamming and distortion by 1-2 mm;
- before assembly, lubricate the outer polished surfaces of the piston connector and the body of 15 valves with a thin layer of TsIATIM-221 lubricant;
- before assembly, cover the surface of diaphragms 7 and 8 with a thin layer of talc, and grease the groove of the shoulder of diaphragm 7 to facilitate rotation of the cover relative to the body with a thin layer of castor oil or NG-213 liquid;
- during assembly, straighten diaphragm 7 so that its shoulder goes behind the protrusions on the amplifier case and presses against the inner diameter of the case;
- tighten the nut securing piston 5 to a torque of 5.5-8 Nm (0.55-0.8 kgf m);
- when inserting cover 6 into body 11, make sure that diaphragm 7 does not wrap.
After assembly, check the operation of the amplifier in the following order:
- connect the non-return valve 1 of the amplifier with a hose to a source of vacuum, for example, to the inlet pipe of a running engine; connect the end of the tube 2 (see Fig. 1) in the plug 5 with a hose to a vacuum gauge;
- create a vacuum of about 70 kPa (0.7 kgf / cm 2) in the amplifier and close the valve on the vacuum pipeline. Within 10 s, the vacuum should not change by more than 4 kPa (0.04 kgf / cm 2).
After checking, set a distance of 131-133 mm between the mating surface of the amplifier housing and the center of the pusher eye, as indicated in fig. 7.6 and tighten the eye nut.
Proper operation of the main brake cylinder is possible if the gap between the head of the adjusting bolt 4 and the mating surface of the cover 6 of the vacuum booster is 1.35-1.65 mm.
To set this gap, loosen the lock nut and turn the bolt 4. After adjusting, tighten the lock nut.
It is necessary to assemble the amplifier with the main cylinder and install it on the car in the reverse order of disassembly.