The brake booster utilizes the difference between the engine vacuum and the atmospheric pressure to generate a power boost. Therefore, the brake booster function can be checked by conducting the following inspection.
1. Airtightness function check
Generating a power boost requires that the vacuum inside the brake booster be maintained, that the constant pressure chamber and variable pressure chamber be completely closed off by the vacuum valve, and that air must flow from the air valve. (1) Stop the engine after running it for 1 to 2 minutes. Vacuum will be allowed into the brake booster. (2) Depress the brake pedal several times. When doing this, if the pedal position is higher 2nd or 3rd time than it was the 1st time, the check valve or vacuum valve is closed, the air valve is open, and air is being let in. From this it can be determined that the airtightness of each valve is normal.
2. Operation check
If the engine is started while there is no vacuum in the brake booster, the vacuum valve is closed, and the air valve is open, vacuum will be allowed into the constant pressure chamber. The brake pedal condition at this time can be used to check the power boost operation.
(1) With the engine stopped, depress the brake pedal several times. Air will be allowed into the constant pressure chamber.
(2) Start the engine with the brake pedal depressed. Vacuum will be generated and a pressure difference will be generated between the constant pressure chamber and the variable pressure chamber. If the brake pedal sinks down a little bit at this time, it can be determined that a normal power boost has been generated. 3. Load airtightness function check
If the engine is turned OFF with the brake pedal depressed, the pedal condition can be used to check for vacuum leaks from the constant pressure chamber. (1) Depress the brake pedal while the engine is running. (2) Turn OFF the engine with the brake pedal depressed. In the hold state, the pressure difference between the constant pressure chamber and the variable pressure chamber will be held constant. Therefore, if there is no change in the brake pedal height while continuing to hold it for 30 sec, then it can be determined that the check valve and vacuum valve are closed normally and that there are no problems with the constant pressure chamber.