Vacuum Brake Booster: Testing and Inspection

POWER BRAKE UNIT FUNCTION CHECK (SIMPLE METHOD)
Step 1
1. With the engine stopped, depress the pedal several times.
2. With the pedal depressed, start the engine.
3. If the pedal moves down slightly immediately after the engine starts, 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 the check valve and vacuum hose for damage and examine the installation. Repair if necessary, and inspect it again.

Step 3
1. Start the engine.
2. Depress the pedal with the usual force.
3. Stop the engine with the pedal 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, inspect the check valve and vacuum hose for damage, and inspect the connection. Repair as necessary and inspect again.
- If the nature of the problem is still not clear after the 3 steps above, follow the more detailed inspect described in "Inspection using gauges" below.


POWER BRAKE UNIT CHECK (INSPECTION USING GAUGES)





^ Connect the Special Service Tool (SST) gauges, vacuum gauge (A), and pedal depression force gauge (B) as shown. Bleed the air from the SST gauges before performing the following tests.

INSPECTION FOR VACUUM LOSS
1. Start the engine.
2. Stop the engine when the vacuum gauge reading reaches 66.6 kPa (500 mmHg, 19.6 inHg).
3. Observe the vacuum gauche for 15 seconds. If the gauge shows 63.4 - 66.6 kPa (475 - 500 mmHg, 18.8 - 19.6 inHg), the unit: is operating.
4. Start the engine.
5. Depress the brake pedal with a force of 196 N (20 kgf, 44 lbs.).
6. With the brake pedal depressed, stop the engine when the vacuum gauge reading reaches 66.6 kPa (500 mmHg, 19.6 inHg).
7. Observe the vacuum gauge for 15 seconds. If the gauge shows 63.4 - 66.6 kPa (475 - 500 mmHg, 18.8 - 19.6 inHg), the unit is operation.

CHECK FOR HYDRAULIC PRESSURE
1. With the engine stopped (vacuum 0 kPa {0 mmHg, 0 inHg}), depress the brake pedal with a force of 196 N (20 kgf, 44 lbs.). If the fluid pressure is within the specification, the unit is operating.

Fluid pressure: 690 kPa (7 kgf/cm2, 100 psi) min.

2. Start the engine. Depress the brake pedal with a force of 196 N (20 kgf, 44 lbs.) when the vacuum reaches 66.6 kPa (500 mmHg, 19.6 inHg). If the fluid pressure is within the specification, the unit is operating.

Fluid pressure:
Z5 MTX, ATX:
7,160 kPa (73 kgf/cm2,100 psi) min.
BP ATX:
8,040 kPa (82 kgf/cm2, 1166 psi) min.