Ford AT4Z-2005-A Booster Assembly - Brake

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Start the engine and turn it off after one or two minutes. Then, depress the brake pedal several times slowly.

Depress the brake pedal several times with the engine off and make sure that there is no change in the pedal reserve distance. Depress the pedal and start the engine. If the pedal goes down slightly, operation is normal. Start the engine and turn it off after one or two minutes. 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. Depress the brake pedal while the engine is running, then 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 that a new or factory rebuilt unit be installed. Before disconnecting the brake pedal, brake booster or booster push rod, the brake light switch must be removed. With the brake pedal in the at-rest position, pull very lightly rearward on the brake pedal, rotate the switch clockwise 45-degrees and remove the switch. Remove the master cylinder. On 2015 and later models, remove the battery and battery tray. Disconnect the electrical connector from the brake vacuum sensor. Remove the retaining clip holding the hose and wiring harness and position them to the side. Under the dash, remove the lower instrument panel cover. Remove the retaining pin and clip, then disconnect the push rod from the top of the brake pedal. Note: 2011 and later models utilize a one-piece clevis locking pin to connect the push-rod to the brake pedal. Use a 12-point, 11 mm wrench or socket to release the tabs on the pin. The pin is a one-lime-use part and must be discarded and replaced if removed. Remove the booster mounting nuts from inside, then carefully lift the booster unit away from the firewall and out of the engine compartment. To install the booster, reverse the removal steps and test the operation of the brakes before placing the vehicle in normal service. When installing the brake light switch, insert the switch into the bracket and rotate the switch 45-degrees counterclockwise. Be careful not to move the brake pedal when installing the switch or damage to the switch can occur.