Vacuum Brake Booster: Testing and Inspection

POWER BRAKE UNIT FUNCTION CHECK
(Simple method)





Step 1
1. With the engine stopped, depress the pedal a few times.
2. With the pedal depressed, start the engine.
3. If immediately after the engine starts the pedal moves down slightly, the unit is operating.





Step 2
1. Start the engine.
2. Stop the engine after it has run for 1 or 2 minutes.
3. Depress the pedal with the usual force.
4. If the first pedal stroke is long and becomes shorter with subsequent strokes, the unit is operating.
5. If a problem is found, inspect for damage of the check valve or vacuum hose and examine the installation. Repair if necessary, and inspect it once again.





Step 3
1. Start the engine.
2. Depress the pedal with the usual force.
3. Stop the engine with the pedal held depressed.
4. Hold the pedal down for about 30 seconds.
5. If the pedal height does not change, the unit is operating.
6. If there is a problem, check for damage to the check valve or vacuum hose, and check the connection. Repair if necessary and check once again.
If the nature of the problem is still not clear after the 3 steps above, follow the more detailed check described in the "Method-using tester" below.

(Method-using tester)





Connect the SST, vacuum gauge (A), and pedal depression force gauge (B) as shown in the figure. After bleeding the air from the SST, conduct the test as described in the 3 steps below.

Notice: Use a commercially available vacuum gauge and pedal depression force gauge.

a) Checking for vacuum loss





Unloaded condition
1. Start the engine.
2. Stop the engine when the vacuum gauge reading reaches 66.7 kPa (500 mmHg, 19.7 inHg).
3. Observe the vacuum gauge for 15 seconds. If the gauge shows 63.3 - 66.7 kPa (475 - 500 mmHg, 18.7 - 19.7 inHg), the unit is operating.





Loaded condition
1. Start the engine.
2. Depress the brake pedal with a force of 196 N (20 kg, 44 lbs.).
3. With the brake pedal depressed, stop the engine when the vacuum gauge reading reaches 66.7 kPa (500 mmHg, 19.7 inHg).
4. Observe the vacuum gauge for 15 seconds. If the gauge shows 63.3 - 66.7 kPa (475 - 500 mmHg, 18.7 - 19.7 inHg), the unit is operating.

b) Checking for hydraulic pressure





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1. If with the engine stopped (vacuum 0 kPa (0 mmHg, 0 inHg)) the fluid pressure is within the specification, the unit is operating.





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2. Start the engine. Depress the brake pedal when the vacuum reaches 66.7 kPa (500 mmHg, 19.7 inHg). If the fluid pressure is within the specification, the unit will operate.