Expedition 4WD V8-5.4L SOHC VIN 5 (2005)
Vacuum Brake Booster: Description and Operation
Brake Booster
The power brake booster is a dual diaphragm, vacuum-assisted power brake booster.
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reduces brake pedal pressure and travel distance.
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is divided into separate vacuum and atmospheric pressure chambers by a diaphragm.
If the power assist fails, the brake system will continue to operate with increased brake pedal effort.
Hose and Check Valve
The power brake booster check valve:
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closes when the engine is turned off.
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in the closed position, traps engine vacuum in the power brake booster.
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retains vacuum to provide several power-assisted brake applications with the engine off.
