F 250 2WD LD Pickup V8-5.4L SOHC VIN L (1997)
Vacuum Brake Booster Check Valve: Testing and Inspection
To test the function of the power brake booster check valve:
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Start and run the engine for at least 10 seconds.
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Operate the brake pedal to check for power assist.
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Disconnect the vacuum booster hose from the power brake booster.Do not remove the check valve from the power brake booster.
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There should be enough vacuum retained in the power brake booster for at least one more power-assisted brake operation