Vacuum Brake Booster: Testing and Inspection

Power Brake Unit Function Check (Simple Method)

Note Replace power brake unit assembly as necessary.

Step 1
1. With the engine stopped, depress the pedal several times.
2. With the pedal depressed, start the engine.
^ If the pedal moves down slightly, immediately after the engine starts, the unit is operating.
^ If a problem is found, inspect for damage on the check valve or vacuum hose, and examine the installation. Repair as necessary, and inspect it again.

Step 2
1. Start the engine.
2. Stop the engine after idling for 1 or 2 minutes.
3. Depress the pedal with the usual force.
^ 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 on the check valve or vacuum hose, and examine the installation. Repair as 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 held depressed.
4. Hold the pedal down for about 30 seconds.
^ If the pedal height does not change, the unit is operating.
^ If a problem is found, inspect for damage on the check valve or vacuum hose, and examine the installation. Repair as necessary, and inspect it again.

Power Brake Unit Function Check (Inspection Using the Testers)





1. Connect the Special Service Tools (SSTs), vacuum gauge, and pedal depression force gauge as shown.

Note
^ Use commercially available gauges and pedal depression force gauge.
^ Bleed the air from the SST at gauge A.

2. After bleeding the air from the SST conduct the test as described in the following steps.

Checking for Vacuum Loss
1. Start the engine.
2. Stop the engine when the vacuum gauge reading reaches 66.7 kPa (500 mm-Hg, 19.7 in-Hg).
3. Observe the vacuum gauge for 15 seconds.
^ If the gauge shows 63.3 - 66.7 kPa (475 - 500 mm-Hg, 18.7 - 19.7 in-Hg), the unit is operating.
^ If a problem is found, inspect for damage on the check valve or vacuum hose, and examine the installation. Repair as necessary, and inspect it again.
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 66.7 kPa (500 mm-Hg, 19.7 in-Hg).
7. Observe the vacuum gauge for 15 seconds.
^ If the gauge shows 66.3 - 66.7 kPa (475 - 500 mm-Hg, 18.7 - 19.7 in-Hg), the unit is operating.
^ If a problem is found, inspect for damages on the check valve or vacuum hose, and examine the installation. Repair as necessary, and inspect it again.

Checking for Hydraulic Pressure





1. When the engine is stopped (vacuum 0 kPa (0 mm-Hg, 0 in-Hg)) and the fluid pressure is within the specification, the unit is operating.





2. Start the engine. Depress the brake pedal when the vacuum reaches 66.7 kPa (500 mm-Hg, 19.7 in-Hg).
^ If the fluid pressure is within the specification, the unit is operating.
^ If the fluid pressure is not within the specification, inspect for damage on the check valve or vacuum hose, and fluid leakage of the brake hydraulic line. Repair as necessary, and inspect it again.