Operation Check When Not Using Measuring Devices

When an operation check is performed with no measuring devices, a faulty part cannot be identified correctly. But it is possible to identify the outline of the defect by performing the check according to the following procedures.

• Air tightness check 

1. Start the engine, and idle it for 1 to 2 minutes, then turn it OFF.
2. Depress the brake pedal several times applying the normal pedal force.
   NOTE: The pedal stroke should be the longest at the 1st depression, and it should become shorter at each successive depression.
3. If no change occurs in the pedal height when pressed, the vacuum booster assembly is faulty.
   Fig 1: Depressing Brake Pedal

   Courtesy of SUBARU OF AMERICA, INC.
   NOTE:

   • In case of defective operation, inspect the condition of the check valve, the vacuum hose, the seal sub assembly and the seal engagement surface of the vacuum booster assembly.
   • If parts are damaged, or the sealing surface of the vacuum booster assembly has a defect such as flaking paint, damage or rust, it may cause negative pressure leakage. Therefore, replace the parts and perform the test again.
   • If no improvement is observed, check precisely with gauges.

• Check operation 

1. While the engine is OFF, depress the brake pedal several times applying the same pedal force, to check for a change in pedal height.
   Fig 2: Checking Brake Pedal

   Courtesy of SUBARU OF AMERICA, INC.
2. With the brake pedal depressed, start the engine.
3. As the engine starts, the brake pedal should move slowly toward the floor. If the pedal height does not change, the vacuum booster assembly is faulty.
   NOTE: If a faulty part is detected after inspection, check precisely with measuring devices.

• Loaded air tightness check 

  Depress the brake pedal while the engine is running, and turn the engine to OFF while the pedal is depressed.

  Keep the pedal depressed for 30 seconds. If the pedal height does not change, the function of vacuum booster assembly is normal. If the pedal height increases, it is faulty.

  NOTE: If a faulty part is detected after inspection, check precisely with measuring devices.