When Using Measuring Device

WARNING: This page is about a different car, the 2022 Subaru WRX. However, it is still accessible from the selected car via links, so may be relevant.

NOTE:

When using a measuring device to check operation, connect the measuring device as shown in the figure. After bleeding air from the pressure gauge, perform each check.

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Air tightness check

Start the engine and keep it running at idle until vacuum pressure indicates 66.7 kPa (500 mmHg, 19.69 inHg) while the brake pedal is not depressed.

Courtesy of SUBARU OF AMERICA, INC.
Stop the engine and check the vacuum pressure.
If the value matches the following standard, the vacuum booster assembly function is normal.

Standard

The range of vacuum pressure drop within 15 seconds after stopping the engine is 3.3 kPa (25 mmHg, 0.98 inHg) or less

If a faulty part is detected after inspection, it may result from one of the following causes.
- Check valve malfunction
- Leak from vacuum hose
- Leak from shell joint section or stud bolt welded section
- Damaged diaphragm
- Leak from valve body seal and bearing section
- Leak from plate and seal assembly section
- Leak from poppet valve assembly section
- Loaded air tightness check

Start the engine and depress the brake pedal with a pedal force of 196 N (20 kgf, 44 Ibf).
Keep the engine running at idle and the pedal depressed until vacuum pressure of the vacuum gauge indicates 93 kPa (697 mmHg, 27.47 inHg).

Courtesy of SUBARU OF AMERICA, INC.
Stop the engine and check the vacuum pressure.
If the value matches the following standard, the vacuum booster assembly function is normal.

Standard

The range of vacuum pressure drop within 15 seconds after stopping the engine is 3.3 kPa (25 mmHg, 0.98 inHg) or less

If a faulty part is detected after inspection, refer to "AIR. TIGHTNESS CHECK". Ref. to BRAKE>BRAKE BOOSTER>INSPECTION .
If the vacuum booster assembly is faulty, replace it with a new part.
- Lack of boost action check

Turn the engine OFF, and set the value of the vacuum gauge to "0".
Check the brake fluid pressure when the brake pedal is depressed. The pressure must be greater than the specification listed.

Brake pedal force: N (kgf, lbf)	147 (15, 33)	294 (30, 66)
Brake fluid pressure: kPa (kgf/cm² , psi)	380 (3.8, 55)	1465 (14.9, 212)

Boosting action check

Set the vacuum gauge reading to 93 kPa (697 mmHg, 27.47 inHg) with the engine running.
Check the brake fluid pressure when the brake pedal is depressed. The pressure must be greater than the specification listed.

Brake pedal force: N (kgf, lbf)	147 (15, 33)	294 (30, 66)
Brake fluid pressure: kPa (kgf/cm² , psi)	9218 (93.9, 1336)	16120 (164, 2338)