Components of installation of the vacuum booster of brakes
The brake booster servo does not need regular maintenance, except for periodic checks of the condition of the vacuum hose. The components of the installation of the vacuum brake booster are shown in the illustration above.
Check of serviceability of functioning of the vacuum amplifier
1. Without starting the engine, depress the foot brake pedal several times. Check that there is no change in pedal back travel (see Section Foot brake pedal adjustment).
2. Keeping the pedal depressed, start the engine. If immediately after starting the pedal slightly «fails», therefore, the vacuum brake booster is working properly.
Vacuum booster leak test
1. Run the engine for a couple of minutes, then shut it off. Slowly depress the foot brake pedal several times. If the pedal stroke gradually decreases with each squeeze, stabilizing at the third or fourth stroke, then the tightness of the vacuum booster assembly is not broken.
2. Depress the foot brake pedal while the engine is running. Keeping the pedal depressed, turn off the engine. If after 30 seconds of keeping the pedal depressed, its reserve stroke does not change, therefore, the tightness of the vacuum booster assembly is not broken.
Checking the hydraulic booster
1. Check if the battery is fully charged.
2. With the ignition off, press the brake pedal at least 4 times.
Note. As the pressure in the system decreases, the pedal travel will decrease and the applied force will increase.
3. Install pressure gauges and force meter (refer to accompanying illustration) and bleed the brake system (see Section Foot brake pedal adjustment).
4. When the hydraulic brake booster is not working, press the brake pedal with a force of 245 N. The pressure in the front brake circuit must be more than 14.5 bar, and in the rear brake circuit - the left one. Increase the pressing force to 343 N, while the pressure in the front brake circuit should be more than 20.6 bar, and in the rear brake circuit - zero.
5. With the hydraulic brake booster running, turn on the ignition and wait until the hydraulic block pump stops working. Press the brake pedal with a force of 49 N. The pressure in the front brake circuit should be 13–25 bar, and in the rear brake circuit 16–28 bar. Increase the pressing force to 98 N, while the pressure in the front brake circuit should be 32–45 bar, and in the rear brake circuit 35–47 bar. Increase the pressing force to 147 N, while the pressure in the front brake circuit should be 53-65 bar, and in the rear brake circuit - 55-67 bar. Increase the pressing force to 196 N, while the pressure in the front brake circuit should be 72-84 bar, and in the rear brake circuit - 75-87 bar.
Removing the vacuum booster
1. The vacuum brake booster unit cannot be repaired and must be replaced as an assembly in case of failure.
2. Disconnect the vacuum hose connected to the booster from the engine intake manifold. Be careful not to damage the hose when removing it from the fitting on the booster assembly.
3. Give the fixing nuts and carefully remove the main brake cylinder from the assembly of the vacuum booster (see Section Removal and installation of the main brake cylinder (GTZ)), be careful not to kink or twist the hydraulic lines.
4. In the passenger compartment, find the node for connecting the pusher rod of the vacuum booster to the foot brake pedal, - (use a flashlight if necessary). Disconnect the return spring first, then remove the cotter pin, release the roll pin and disconnect the pushrod split pin from the pedal arm.
5. From the passenger compartment on the left under the instrument panel, release the four nuts securing the vacuum booster assembly to the bulkhead of the engine compartment (refer to accompanying illustration), – use a flashlight if necessary.
6. Go to the engine compartment and remove the vacuum booster assembly from the rear bulkhead. Pull the assembly strictly along the axis of its installation until the pusher rod is completely released. Remove the assembly from the engine compartment.
Installing and adjusting the vacuum booster
1. Installation is carried out in the reverse order. Tighten all fasteners to the required torque. Don't forget to replace the split pin that secures the push rod to the pedal. Track reliability of fixing of a returnable spring.
2. When replacing the vacuum booster, check / adjust the installation dimensions:
- a. Measure the protrusion of the pusher above the mating surface of the vacuum booster assembly with the GTZ (refer to illustration). Write down the result of the measurement, designating it as a size «A»;
- b. Measure the distance from the mating surface of the mounting flange to the end of the GTZ (refer to illustration). Write down the result of the measurement, designating it as a size «IN»;
- c. Measure the distance from the end of the GTZ to the bottom of the pocket in the piston for the fit of the pusher rod (refer to illustration). Write down the result of the measurement, designating it as a size «WITH»;
- d. Subtract dimension B from dimension C to obtain the seat clearance of the pusher rod, then subtract dimension A from the result (refer to illustration);
- e. Compare the result of the calculation with the requirements Specifications, if necessary, make an appropriate adjustment to the length of the pusher (see below). If dimension A is less than the pocket depth in the GTZ piston (N-E), the stem must be shortened, otherwise lengthened.
3. If the seat gap is out of range, loosen the knurled bit on the end of the stem and turn the adjusting rod until the desired result is achieved (refer to accompanying illustration). After completing the adjustment, tighten the locknut firmly and recheck.
4. Install in place in the GTZ and connect the vacuum hose to the vacuum booster assembly. Track reliability of a tightening of a collar of fastening of a hose on the receiving union.
5. Adjust the installation height and free play of the foot brake pedal (see Section Foot brake pedal adjustment).
6. Before starting the operation of the car, make sure that the brake system is functioning properly.