Pic. 8.8. Brake booster device: 1 – a pusher rod to the main brake cylinder; 2 - check valve with a rubber gasket; 3 – membrane housing; 4 – a pusher rod from a brake pedal
The brake booster device is shown in fig. 8.8.
The brake booster uses the vacuum created by the engine at the inlet and loses part of its reinforcing effect in the event of a leak in the rubber seal. If air is escaping when the hose is slightly wiggled, the rubber seal on the booster is leaking and should be replaced immediately.
Sequence of work
1. Stop the engine, press and hold the brake pedal several times.
2. Start the engine. The pedal should move forward a little. If this does not happen, the following reasons are possible:
Pic. 8.9. If air passes when the vacuum hose is slightly wiggled, the rubber seal on the booster is leaking and needs to be replaced as soon as possible
- leaky vacuum hose from intake pipe to booster (pic. 8.9). In this case, the hose must be replaced;
Pic. 8.10. Disconnect the hose to check the valve (arrow) from amplifier
- Defective check valve in the vacuum hose. Disconnect the hose to check the valve (pic. 8.10, arrow) from the amplifier. In good condition, air must pass through the hose when blowing out and not pass when drawn in;
- Worn rubber ring between master cylinder and booster. Replacement requires dismantling of the master cylinder;
- clogged air filter on booster lifter. Remove the filter from the push rod with a wire hook. Cut the new filter to the middle and install on the pusher rod. Make sure that the filter fits securely around the stem, otherwise unfiltered air may enter the amplifier;
- Amplifier diaphragm damaged. In this case, repair is not possible. The amplifier must be replaced as an assembly.
Brake pedal and brake pads
The free play of the brake pedal should be no more than a third of the entire pedal travel. If the pedal is pushed further (check by hand), it is necessary to check the disc brake mechanisms - severe wear or jamming of the pad linings, corrosion of the brake caliper are possible. Checking by pressing the pedal does not replace the inspection of the pad linings: the brake cylinder piston pushes the pads with worn linings so far that the return to the original position after releasing the pedal is also large. The pedal travel thus remains almost unchanged as long as the pads are not worn to a minimum value. If the pedal travel decreases with repeated pressing, then there may be air in the system - bleed the system.