Fig. 8.8. Brake booster device: 1 – push rod to the main brake cylinder; 2 – check valve with rubber gasket; 3 – membrane body; 4 – push rod from the brake pedal
The brake booster device is shown in Fig. 8.8.
The brake booster uses the vacuum created by the engine at the intake and loses some of its boosting effect if the rubber seal connection is not tight. If air passes through when the hose is slightly rocked, the rubber seal on the booster is not tight and should be replaced immediately.
Sequence of works
1. Stop the engine, press the brake pedal several times and hold it down.
2. Start the engine. The pedal should move forward slightly. If this does not happen, the following reasons are possible:
Fig. 8.9. If air passes through when the vacuum hose is gently rocked, the rubber seal on the booster is not airtight and needs to be replaced immediately
- the vacuum hose from the intake pipe to the booster is not tight (Fig. 8.9). In this case, the hose must be replaced;
Fig. 8.10. To check the valve, disconnect the hose (arrow) from the booster
- the check valve in the vacuum hose is faulty. To check the valve, disconnect the hose (fig. 8.10, arrow) from the amplifier. In good condition, air should pass through the hose when blowing out and not pass through when drawing in;
- the rubber ring between the master cylinder and the booster is worn out. To replace it, the master cylinder must be removed;
- the air filter on the booster pushrod is clogged. Remove the filter from the pushrod with a wire hook. Cut the new filter to the middle and install it on the pushrod. Make sure that the filter fits securely around the pushrod, otherwise unfiltered air may get into the booster;
- the amplifier membrane is damaged. In this case, repair is not possible. The amplifier must be replaced as a whole.
Brake pedal and brake shoe linings
The free travel of the brake pedal should be no more than a third of the total pedal travel. If the pedal is pressed further (check with your hand), it is necessary to check the disc brake mechanisms - there may be severe wear or jamming of the pad linings, corrosion of the brake caliper. Checking by pressing the pedal does not replace the inspection of the pad linings: the piston of the brake cylinder pushes the pads with worn linings so far that the return stroke to the initial position after releasing the pedal is also large. The pedal stroke, therefore, remains almost unchanged until the linings are worn to a minimum value. If the pedal stroke becomes smaller with repeated pressing, then there may be air in the system - bleed the system.