If the brake pedal on a vehicle becomes hard to press, its resistance could be related to a number of different problems, including an obstruction of the brake lines or an issue with the brake booster. Some common problems associated with brake boosters include defective check valves and leaky vacuum hoses.
An obstruction in the brake line can prevent brake fluid from properly flowing throughout the system, which can make it difficult to depress the brake pedal. These obstructions could be caused by a piece of metal or rust becoming lodged within the brake line or a pinch in the line. A thorough examination of the brake lines is necessary to determine if this is where the problem lies, and replacement of the lines is necessary if an obstruction is discovered.
Almost all vehicles use a vacuum brake booster system that helps make it possible to brake with less pedal pressure. According to About.com, these brake boosters provide the equivalent braking strength of 10 men. In many cases, braking issues are caused by a leak in one of the vacuum hoses, which prevents the booster from building up enough negative pressure. If no leak is discovered, the problem is likely related to a bad booster. Still, there are also other possible causes, so it may be necessary to have the problem looked at by a mechanic.