Operation Check (With Gauge)

Check with gauge 

Connect the gauge as shown in the figure. After bleeding air from the pressure gauge, perform the checks.

Fig 1: Identifying Pressure Gauge, Vacuum Gauge, Adapter Hose And Vacuum Hose

Courtesy of SUBARU OF AMERICA, INC.

Air tightness check 

1. Start the engine and keep it running until vacuum pressure indicates point A of the vacuum gage = 66. 7 kPa (500 mm Hg, 19. 69 in. Hg). Do not depress the brake pedal at this time.
   Fig 2: Identifying Pressure Gauge And Vacuum Gauge

   Courtesy of SUBARU OF AMERICA, INC.
2. Stop the engine and check the gauge. If the vacuum pressure drop within 15 seconds after stopping the engine is less than 3. 3 kPa (25 mm Hg, 0. 98 in. Hg), the function of brake booster is normal. If faulty, the cause may be one of the following.

• 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 

1. Start the engine and depress the brake pedal with a pedal force of 196 N (20 kgf, 44 lb). Keep the engine running and keep the pedal pressed until a vacuum of point B = 66. 7 kPa (500 mm Hg, 19. 69 in. Hg) is indicated on the vacuum gauge.
   Fig 3: Identifying Pressure Gauge, Vacuum Gauge And Pedal Force Gauge

   Courtesy of SUBARU OF AMERICA, INC.
2. Stop the engine and check the vacuum gauge. If the vacuum pressure drop within 15 seconds after stopping the engine is less than 3.3 kPa (25 mm Hg, 0.98 in. Hg), the function of brake booster is normal.

   If defective, refer to "AIR TIGHTNESS CHECK". < Refer to INSPECTION , BRAKE BOOSTER. >

3. If the brake booster is faulty, replace the it with a new part.

Lack of boost action check 

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

Boosting action check 

Set the vacuum gauge reading to 66. 7 kPa (500 mm Hg, 19. 69 in. Hg) with the engine running. Then, check the fluid pressure when the brake pedal is depressed. The pressure must be greater than the specification listed.