The lines for the rear brakes on most vehicles consist of steel tubing that run from the master cylinder to the rear brake cylinders. The lines for the front brakes are made of steel tubing with short flex hoses at the wheel end. The flex hose runs from the frame or body of the vehicle to the front wheel brake cylinder to allow for turning. Both the steel tubing and the rubber flex hoses are subject to aging and damage. The most common causes of steel brake line failure are rust and wear from the clamps that secure them to the frame or body of the vehicle. Occasionally a brake line can be damaged by highway debris kicked up by the tires. The most common cause of flex hose failure is aging.
The most obvious sign of a brake line leak is a loss of pedal power. Pedal is the amount of travel in the brake pedal before the brakes engage. If you have to push the brake pedal half way to the floor board before you feel any resistance you certainly have a problem in the braking system. The problem could be the failure of self-adjusting brakes to adjust, air in the system from a lack of brake fluid or brakes that have not been bled properly or a leak in a brake line. If you are experiencing a lack of pedal, first check the brake fluid level in the master cylinder. If the level is okay, you may have air in the brake lines or the brake pads are severely worn. If the brake fluid level is low, you likely have a leaking brake line or a blown wheel cylinder.
The next sign of a leaking brake line is brake fluid on the ground under the car. This will usually show up after the car has been sitting overnight. If brake fluid is detected, an under carriage inspection is in order. Jack up the vehicle and properly support it with jack stands. Look for rusting brake lines and the presence of fluid. Pay particular attention to the clamps that secure the lines to the body of the vehicle. Rust and vibration can cause these clamps to wear through the brake line.
A leaking or blown brake cylinder can be found by inspecting the back side of the wheels. Leaking brake fluid will leave streaks on the back side of the tires and wheels. Blown brake cylinders are usually caused by the self-adjusters not working properly or by not changing the brake shoes soon enough.
A leaking flex hose will also leave brake fluid on the ground and possibly on the wheel or chassis. The flex hoses can be inspected for leaks by turning the front wheels all the way to one side. If the outer rubber is cracked or brake fluid is present the hose should be replaced.
Be aware that any time a brake system component is replaced the brake system will need to be bled. Bleeding the brakes is a process that removes the air from the brake system. If you have to pump the brake pedal a few times before you get a firm pedal, check your vehicle for brake line leaks or severely worn brake shoes or pads.
Your life and the lives of others depend on your vehicle's brakes. Maintain the fluid level, inspect the pads and shoes often and replace them when needed and watch for a soft pedal or fluid leaks.