Someone suggested the brake booster is faulty. To check, pump the brakes lots of times with the engine off to make sure there is no vacuum left. Pedal should be high. Keep foot on brake and start the engine. Pedal should drop and then stop. If not, then there is no booster action. The booster has a filter in the back which may get blocked. You have to disconnect the pedal from the booster, unbolt the master cyl. from the booster, and remove the booster from the fire wall. Other failure modes are the check valve in the vacuum hose and a leaking diaphrame inside the booster. It is actually very simple.