Most of the car's brakes are assisted by vacuum. If you pump the brakes off your car, you get to find a normal pump, and they in due course of time hardens as the vacuum reservoir gets exhausted. Now if your car is being used for weeks together, the vacuum might recede as the system isn't designed to hold the vacuum for long, and that’s why you tend to get the hard pedal feel. You can test this hypothesis easily by turning off the car and pumping the brakes.
The probable reasons and frequent solutions to get rid of the hard brake pedal are:
Vacuum or lack of vacuum pressure is the most common cause of a hard brake pedal, and therefore, it is the foremost thing to look at when the brake pedal becomes rock hard. Another possible reason for a hard pedal could be the combination valve and in particular the Pressure Differential Valve within it. A thorough inspection of the whole system should help you identify such underlying issues of a hard brake pedal.
If you are completely unaware and do not know how to take the correct action, engage a professional mechanic at Eurobahn BMW MINI Mercedes-Benz Audi of Greensboro.