Vacuum Brake Booster: Testing and Inspection
POWER BRAKE UNIT INSPECTIONWarning:
^ The following inspection methods are simple inspection methods to judge the function of the power brake unit.
^ If there is a malfunction in the power brake unit, replace the power brake unit as a component.
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 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.
^ If a problem is found, inspect for damage of the vacuum hose, and vacuum tank. Repair if necessary, and inspect it again.
Step 3
1. Start the engine.
2. Depress the pedal with usual force.
3. If the pedal height does not change, the unit is operating.
4. Hold the pedal down for about 30 s.
5. If the pedal height does not change, the unit is operating.
Power Brake Unit Function Check (inspection Using The Testers)
1. Connect the SSTs, vacuum gauge, and pedal depression force gauge as shown in the figure to bleed the air from the SSTs and brake line. (Bleed the air from the SSTs using a air bleed valve A.)
Checking for vacuum loss (unloaded condition)
1. Stop the engine when the vacuum gauge reading reaches 66.7 kPa (500 mmHg, 19.7 inHg).
2. Observe the vacuum gauge for 15 s.
^ If the gauge shows 63.3-66.7 kPa (475-500 mmHg, 18.7-19.6 inHg), the unit is operating.
^ If not, inspect for damage on the check valve or vacuum hose, and examine the installation. Repair as necessary, and inspect it again.
Checking for vacuum loss (loaded condition)
1. Start the engine.
2. Depress the brake pedal with a force of 196 N (20 kgf, 44 lbf).
3. Stop the engine when the vacuum gauge reading reaches 66.7 kPa (500 mmHg, 19.7 inHg).
4. Observe the vacuum gauge for 15 s.
5. If the gauge shows 63.3-66.7 kPa (475-500 mmHg, 18.7-19.6 inHg), the unit is operating.
Checking for hydraulic pressure
1. When the engine is stopped (vacuum 0 kPa (0 mmHg, 0 inHg)) and the fluid pressure is within the specification, the unit is operating.
Power brake unit fluid pressure when pedal depressed at 200 N (20 kgf, 44 lbf)
At 0 kPa (0 mmHg, 0 inHg): 590 kPa (6.02 kgf/cm2, 85.6 psi)
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 is operating.
^ If the fluid pressure is not as specified, inspect for damage to the check valve or vacuum hose, and fluid leakage of the hydraulic line. Repair as necessary, and inspect again.
Power brake unit fluid pressure when pedal depressed at 200 N (20 kgf, 44 lbf)
At 66.7 kPa (500 mmHg, 19.7 inHg): 8,780 kPa (89.53 kgf/cm, 1,273 psi)