Mountaineer AWD V8-4.6L (2010)
Brake Master Cylinder: Testing and Inspection
Brake Booster
Component Tests
Brake Booster
1. Disconnect the check valve from the brake booster and connect a suitable vacuum/pressure tester to the booster side of the check valve.
2. Apply the parking brake, start the engine and place the transmission in NEUTRAL.
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Allow the engine to reach normal operating temperature.
3. NOTE: Subtract approximately 4.0193 kPa (1 in-Hg) from the specified reading for every 304.8 m (1,000 ft) of elevation above sea level.
Verify that vacuum is available at the check valve with engine running at normal idle speed.
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The vacuum gauge should read between 51-74 kPa (15-22 in-Hg).
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If specified vacuum is available, stop the engine, connect the check valve and continue with Step 5.
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If specified vacuum is not available, continue with Step 4.
4. Disconnect the check valve from the vacuum hose and verify that the specified vacuum is available at the hose with the engine at idle speed and
the transmission in NEUTRAL.
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If specified vacuum is available, stop the engine, install a new check valve and continue with Step 5.
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If specified vacuum is not available, stop the engine, connect the vacuum hose to the check valve and refer to Engine to diagnose the no/low
vacuum condition.
5. Apply the brake pedal several times to exhaust all vacuum from the system.
6. Apply the brake pedal and hold it in the applied position. Start the engine and verify that the brake pedal moves downward after the engine starts.
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If the brake pedal moves, the brake booster is operating correctly.
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If the brake pedal does not move, install a new brake booster. Refer to Power Brake Assist.
7. Operate the engine a minimum of 20 seconds at idle. Stop the engine and let the vehicle stand for 10 minutes, then apply the brake pedal. The
brake pedal feel should be the same as that noted with the engine operating.
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If the brake pedal feels hard (no power assist), install a new brake booster check valve and retest.
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If condition still exists, install a new brake booster. Refer to Power Brake Assist.
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If the brake pedal feels the same as noted with the engine operating, the check valve is functioning properly.
