A hard brake pedal is most often caused by a lack of vacuum, but can also be caused by using the wrong hose, using a defective brake booster check valve or using a defective booster. It is also possible to run a combination valve where the valve is no longer centered, which can cause a hard pedal in a person's car.
Drum brakes that are stuck can be another cause of hard pedal as can a pedal ratio of 1:1. It is recommended for drivers to make sure that their wheel cylinders are moving freely if they have drum brakes and that their pedal ratio is 4:1. It is also important for a person to make sure that they have a brake booster that is appropriate for the weight of their vehicle. Too many people use a small brake booster for a heavy vehicle, which can result in hard pedal.
When a brake pedal is hard to press, it makes it harder to stop. This can lead to accidents if not corrected. The most common cause of the brake pedal, not enough vacuum, can be corrected by adding enough vacuum to the car. The car should have a 18-inch vacuum for optimal results. Anything less than this will make it more difficult for a person to push the pedal. If the problem persists then the car should be taken in to a garage to be fixed.