Let's clarify what an extremely hard pedal is. Neither my '93 nor my 2000 Taurus have extremely hard pedals. When the engine is off and the vacuum in the booster is exhausted the pedal is firm after travelling a short distance, not even hard. When the engine starts and the booster gets vacuum the pedal softens up and there is some more give to the pedal than without the booster working. When the car is underway the pedal is high when brakes are applied indicating that the rear brakes are adjusted up. If pedal is low rear brakes need adjusting. The pedal feel is never even hard, but it is firm.
If your pedal is extremely firm with no give when engine is operating then the booster may not be working. Check for vacuum there.
Poor braking performance could be due to air in the master, or a faulty master. Try keeping pressure on the brake with the engine running and see if pedal drops. This would be a sign of fluid bypassing the seals in the master, but not necessarily leaking outside. Check for air in the master by applying the brake (engine off) and just loosening one brake line at the master, only fluid should come out, if you see any bubbles then you have air in master. Allow pedal to go to floor and tighten line, release the brake. Repeat step untill no more air, then do other line (I think you should have 2 lines).
To bleed the lines and brakes start at the wheel farthest from the master cylinder and work toward the master.
Hope this helps.
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Art
2000 Taurus SEL Wagon 3.0 Vulcan (daily driver)
1993 Taurus GL Wagon 3.8 Essex
1991 Mercury Grand Marquis LS 5.0
1986 Chevrolet 3/4 ton pickup 4x4 350 with turbo400 and 208 transfer case
1978 Chevrolet 3/4 ton pickup 4x4 custom 6.2 na diesel with turbo400 and 203 transfer case
Planning 2008 Taurus X in a year
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