Vacuum Brake Booster: Testing and Inspection
INSPECTION1. OPERATION CHECK (WITHOUT GAUGES)
CAUTION: When checking operation, be sure to securely apply the hand brake.
^ Checking without gauges
This method cannot determine the exact portion which has failed, but it can provide a rough understanding of the nature of the failure if checking is conducted in accordance with the following procedures.
^ Air tightness check
Start engine, and run it for 1 to 2 minutes, then turn it off. Depress brake pedal several times applying the same pedal force as that used in ordinary braking operations. The pedal stroke should be greatest on the 1st depression, and it should become smaller with each successive depression. If no change occurs in the pedal height while in a depressed state, brake booster is faulty.
NOTE:
^ In the event of defective operation, inspect the condition of the check valve and vacuum hose.
^ Replace them if faulty and conduct the test again.
^ If no improvement is observed, check precisely with gauges.
^ Operation check
1. With engine off, depress brake pedal several times applying the same pedal force and make sure that the pedal height does not vary with each depression of the pedal.
2. With brake pedal depressed, start engine.
3. As engine starts, brake pedal should move slightly toward the floor. If no change occurs in the pedal height, brake booster is faulty.
NOTE: If faulty, check precisely with gauges.
^ Loaded air tightness check
Depress brake pedal while engine is running, and turn off engine while the pedal is still depressed. Keep the pedal depressed for 30 seconds; if no change occurs in the pedal height, brake booster is functioning normally; if the pedal height increases, it is faulty.
NOTE: If faulty, check precisely with gauges.
2. OPERATION CHECK (WITH GAUGES)
CAUTION: When checking operation, be sure to securely apply the hand brake.
^ Checking with gauges
Connect gauges as shown in Figure. After bleeding air from pressure gauges, proceed to each check.
^ Air tightness check
1. Start engine and keep it running until a vacuum of 66.7 kPa (500 mmHg, 19.69 inHg) = point A is indicated on vacuum gauge. Do not depress brake pedal.
2. Stop engine and watch the gauge. If the vacuum drop range is less than 3.3 kPa (25 mmHg, 0.98 inHg) within 15 seconds after stopping engine, brake booster is functioning properly. If defective, the cause may be one of those listed below.
^ Check valve malfunction
^ Leak from vacuum hose
^ Leak from the shell jointed portion or stud bolt welded portion
^ Damaged diaphragm
^ Leak from valve body seal and bearing portion
^ Leak from plate and seal assembly portion
^ Leak from poppet valve assembly portion
^ Loaded air tightness check
1. Start engine and depress brake pedal with pedal force of 196 N (20 kgf, 44 lb). Keep engine running until a vacuum of 66.7 kPa (500 mmHg, 19.69 inHg) = point B is indicated on vacuum clause while the pedal is still depressed.
2. Stop engine and watch vacuum gauge.
If the vacuum drop range is less than 3.3 kPa (25 mmHg, 0.98 inHg) within 15 seconds after stopping engine, brake booster is functioning properly.
^ Lack of boosting action check
Turn off engine, and set the vacuum gauge reading at "0". Then, check the fluid pressure when brake pedal is depressed. The pressure must be greater than the standard value listed.
^ Boosting action check
Set the vacuum gauge reading at 66.7 kPa (500 mmHg, 19.69 inHg)by running engine. Then, check the fluid pressure when brake pedal is depressed. The pressure must be greater than the standard value listed.