When the vacuum booster fails, the force on the brake pedal increases significantly, which negatively affects vehicle control.
If the pedal effort when braking is noticeably greater than usual, check the brake booster with the vehicle stationary.
1. With the engine not running, press the brake pedal five to six times (at intervals of about 5 seconds) and, keeping the brake pedal depressed, start the engine. The brake pedal should move forward.
If this does not happen, check…
2….tightness of the vacuum hose fit in the intake pipe (for clarity, the throttle assembly has been removed)…
3….and in the brake booster housing.
NOTE: The battery and its mounting shelf with the intake noise muffler have been removed for clarity.
4. Remove the battery (see Removing and installing the battery)…
5….and its mounting shelf together with the intake noise muffler (see Removing and installing the battery mounting shelf).
6. To check the operation of the check valve, use a screwdriver to pry up the check valve of the vacuum hose…
7….and remove it from the hole of the sealing bushing of the brake booster.
8. Insert the bulb tip tightly into the check valve and squeeze the bulb. The air should come out through the valve.
9. Release the bulb. If it remains compressed, the valve is OK. If there is no bulb, you can blow through the valve with your mouth.
10. If the check valve leaks air in both directions, replace the vacuum hose assembly with the valve, to do this…
11….holding the seal with a screwdriver…
NOTE: Throttle body removed for clarity.
12….remove the vacuum hose fitting from the intake pipe opening…
13….and remove the vacuum hose assembly with the check valve.
14. Install the parts in the reverse order of removal.
(The text is available on the specified website info portal: FordBook)