Depress the brake pedal several times with the engine off to ensure there is no change in the pedal reserve distance. Start the engine and depress the pedal; if it goes down slightly, operation is normal. For an airtightness check of the vacuum booster, start the engine and turn it off after one or two minutes, then depress the brake pedal several times slowly; if the pedal goes down farther the first time but gradually rises after the second or third depression, the booster is airtight. While the engine is running, depress the brake pedal and stop the engine with the pedal depressed; if there is no change in the pedal reserve travel after holding the pedal for 30 seconds, the booster is airtight. Disassembly of the power unit requires special tools and is not ordinarily performed by the home mechanic; if a problem develops, it's recommended to install a new or factory rebuilt unit. In the engine compartment, remove the nuts attaching the master cylinder to the booster and carefully pull the master cylinder forward until it clears the mounting studs, taking care not to bend or kink the brake lines. For models with a vacuum booster, disconnect the vacuum hose from the power brake booster; for hydraulic boosters, detach the fluid pressure and return lines. In the passenger compartment, remove the retaining pin and brake light switch, then disconnect the pushrod from the top of the brake pedal. Remove the nuts attaching the booster to the firewall, then carefully lift the booster unit away from the firewall and out of the engine compartment. To install the booster, place it into position and tighten the retaining nuts, reconnect the pushrod to the brake pedal, and install the brake light switch. If installing a new vacuum booster, apply a vacuum of approximately 18 to 20 in-Hg to the booster with a hand-held vacuum pump, then measure the protrusion of the pushrod from the face of the booster; if it is not as specified, adjust the length of the pushrod by turning the screw at the end. Install the master cylinder and reconnect the vacuum hose or pressure and return lines as applicable. For models with a hydraulic booster, bleed the air from the booster unit by removing the PCM fuse from the engine compartment fuse block, cranking the engine for a few seconds, checking the power steering fluid level, adding fluid as necessary, and reinstalling the PCM fuse. Start the engine and allow it to idle, turning the steering wheel from stop-to-stop two times before turning off the engine. Depress the brake pedal several times to discharge the accumulator, repeating this procedure until the fluid in the power steering fluid reservoir is free of air bubbles. Finally, carefully test the operation of the brakes before placing the vehicle in normal service.
Posted by FordPartsGiant Specialist 
