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Home >> Ford >> 2006 >> Focus ZX5 SE, Standard >> Repair and Diagnosis >> External Pages >> Different car >> Section 1085 (Brake System - General Information) >> Diagnostic Tests >> Brake System >> Component Tests >> Brake Booster - Vacuum Boost

Brake Booster - Vacuum Boost

WARNING: This page is about a different car, the 2008 Ford RV Cutaway, 2008 Ford Econoline, 2008 Ford E450 Super Duty, and 2008 Ford Cutaway. However, it is still accessible from the selected car via links, so may be relevant.
  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.
    • 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.
  3. Verify that vacuum is available at the booster side of the check valve with the engine running at idle speed.
    • The vacuum gauge should read between 51-74 kPa (15-22 in-Hg) on vehicles not equipped with a vacuum pump and 70-85 kPa (20-25 in-Hg) on vacuum pump-equipped vehicles.
    • If the specified vacuum is available, stop the engine, connect the check valve and continue with Step 5.
    • If the 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.
    • If the specified vacuum is available, stop the engine and install a new check valve.
    • On vehicles not equipped with a vacuum pump, if the specified vacuum is not available, stop the engine, connect the vacuum hose to the check valve and refer to ENGINE SYSTEM - GENERAL INFORMATION article to diagnose the no/low vacuum condition.
    • On vehicles equipped with a vacuum pump, if the specified vacuum is not available, stop the engine and inspect the vacuum hose for kinks, restrictions or leaks, replace if needed. Inspect the accessory drive system. Refer to Inspection and Verification in ACCESSORY DRIVE article. If the accessory drive system is OK, install a new vacuum pump. Refer to POWER BRAKE ACTUATION article.
  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.
    • If the brake pedal moves, the brake booster is operating correctly, release the pedal and continue to Step 7.
    • If the brake pedal does not move, install a new brake booster. Refer to POWER BRAKE ACTUATION article.
  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.
    • If the brake pedal feels hard (no power assist), install a new brake booster check valve and retest.
    • If condition still exists, install a new brake booster. Refer to POWER BRAKE ACTUATION article.
    • If the brake pedal feels the same as noted with the engine operating, the check valve is functioning properly.
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