Without the use of appliances
Note: If the vacuum booster is not working properly, replace the brake booster assembly.
Step 1
1. With the engine off, press the brake pedal several times.
2. With the pedal depressed, start the engine.
3. If the pedal went down a little immediately after starting the engine, the vacuum brake booster is working.
Step 2
1. Start the engine.
2. After 1-2 minutes of operation, stop the engine.
3. Depress the brake pedal several times with normal force.
4. If the pedal travel is long at the first press, but becomes shorter with subsequent presses, no vacuum booster malfunctions have been detected.
Note: If there is a problem, check the vacuum hose or non-return valve and check their installation. If malfunctions are found, eliminate them and once again check the operation of the vacuum brake booster.
Step 3
1. Start the engine.
2. Depress the brake pedal with normal force.
3. Keeping the pedal depressed, stop the engine.
4. Hold down the pedal for approximately 30 seconds.
5. If the pedal height has not changed, there are no faults in the vacuum booster.
Using appliances
1. Connect pressure gauges, install a vacuum gauge and brake pedal force gauge as shown.
1 - vacuum gauge,
2 - manometer,
3 - a device for measuring the force on the brake pedal.
Note:
- Use standard diagnostic gauges to check brake fluid pressure and a conventional force gauge.
- Purge the air from the installed fixture and gauges.
2. After bleeding the assembled system, carry out the following checks:
A) Vacuum reduction test.
With the brake pedal not depressed:
1. Start the engine.
2. Shut off the engine when the vacuum gauge shows a vacuum of 66.7 kPa.
3. Observe the readings of the pressure gauge for at least 15 seconds, if the vacuum is in the range of 64 - 66 kPa, no malfunction of the vacuum booster was detected.
With the brake pedal depressed:
1. Start the engine.
2. Press the brake pedal with a force of 200 N.
3. Keeping the pedal depressed, turn off the engine when the vacuum gauge shows a vacuum of 67 kPa.
4. Observe the readings of the pressure gauge for at least 15 seconds, if the vacuum is in the range of 64 - 66 kPa, no malfunction of the vacuum booster is detected.
b) Checking the brake fluid pressure developed by the master brake cylinder.
1. With the engine off (complete absence of vacuum) press the brake pedal with a force of 200 N. If the brake fluid pressure corresponds to the nominal, no malfunction of the vacuum booster was detected.
- brake fluid pressure (in the absence of vacuum) — not less than 593 kPa
2. Start the engine. When the vacuum indicated by the vacuum gauge reaches 67 kPa (500 mmHg), depress the brake pedal. If the brake fluid pressure is correct, no vacuum booster malfunction has been detected.
- brake fluid pressure (at a vacuum of 67 kPa) — not less than 6950 kPa