Power Brake System

With engine off, depress and release brake pedal several times to remove vacuum from power brake booster. Lightly depress and hold brake pedal. Start engine. If power brake booster is operating properly, brake pedal will fall slightly and then hold. Less effort will be required for brake pedal application. If power brake booster is not operating properly, go to next step. If power brake booster is operating properly, go to step 4).
If brake pedal does not fall slightly and then hold, shut engine off. Disconnect cruise control vacuum hose from check valve at power brake booster. Connect vacuum gauge to cruise control vacuum hose fitting on check valve at power brake booster. Start engine. With engine at normal operating temperature, check vacuum reading. If vacuum is 12 in. Hg or more, replace power brake booster. If vacuum is less than 12 in. Hg, go to next step.
Low vacuum may cause power brake booster to run out of vacuum early which may be mistaken for a brake pedal that goes to the floor. Check for vacuum leaks or improperly tuned engine. Repair vacuum leaks or perform engine tune-up as necessary. Once proper vacuum is obtained, perform power brake booster test again.
Disconnect A/C vacuum control vacuum hose (if equipped) from check valve at power brake booster. Install cap on vacuum hose fitting on check valve. Disconnect cruise control vacuum hose from check valve at power brake booster.
Connect vacuum gauge to cruise control vacuum hose fitting on check valve at power brake booster. Ensure any remaining vacuum hose fittings are plugged.
Start engine. Allow engine to idle until engine is warm and at normal idle speed. Using pliers, close off vacuum supply hose to check valve on power brake booster and note vacuum reading.
Vacuum should not decrease more than one in. Hg within one minute. If vacuum does not decrease more than one in. Hg within one minute, go to next step. If vacuum decreases more than one in. Hg within one minute, repeat procedure to verify vacuum readings again. If vacuum still decreases more than one in. Hg within one minute, replace power brake booster.
Remove pliers from vacuum supply hose. Lightly depress brake pedal by applying 15 lbs. pressure on brake pedal. Hold brake pedal in this position. DO NOT move brake pedal, as brake pedal movement will affect vacuum reading.
Have an assistant use pliers to close off vacuum supply hose to check valve on power brake booster. Wait at least 5 seconds for vacuum to stabilize and then note vacuum reading.
Vacuum should not decrease more than 3 in. Hg within 15 seconds. If vacuum does not decrease more 3 in. Hg within 15 seconds, power brake booster is okay. If vacuum decreases more than 3 in. Hg within 15 seconds, repeat procedure to verify vacuum readings again. If vacuum still decreases more than 3 in. Hg within 15 seconds, replace power brake booster.