I was driving down a driveway with a slight incline. I pressed the brakes and they were very hard to press and vehicle would not stop until I collided with a wall. This is the fourth time that this has happened in the last two years. Each time it has been the brake booster vacuum pump which my mechanics have said is a common problem with this vehicle. One of the previous times my daughter was driving on the highway when the brakes failed and she ended up in a ditch off the shoulder. This is very dangerous and someone is going to get killed if it hasn't happened already.