The brake system of a modern motor vehicle is composed of many components including the brake lines. The brake lines are made up of a series of tubes, pipes and hoses that contain the brake fluid. Air in the brake lines can have an adverse affect on the brake systems ability to stop the car. Under normal conditions air cannot gain access to the brake lines. Air in the brake lines is usually the result of a leak in the brake line or during repairs on the brake system.
The driver often senses that the brake pedal is spongy when pressed if there is air in the brake lines. When the brake pedal is press a piston moves in a cylinder forcing brake fluid from the master cylinder through the brake lines to the brake calipers. While brake fluid will not compress, air does. If there is air in the brake line the air compresses delaying the brake fluid's movement to the calipers.
Each wheel cylinder and the master cylinder include a bleeder screw. Loosen the bleeder screw and have someone press on the brake pedal until brake fluid is forced from the bleeder screw.
Brake lines are routinely bled after any maintenance work on the brake system. Brake lines are also bled anytime air in the brake lines is suspected.
Brakes systems are flushed if the brake fluid is suspected of being dirty or having broken down due to heat. During the flushing process the existing brake fluid is drained from the system and replaced with fresh. The air is bled from the brake system after the new brake fluid is in place.
Brake lines are made of steel tubes and reinforced hoses. The reinforced rubber hoses are used where movement of the line is possible such near the wheels where the suspension of the vehicle can cause the body to ride up and down in relation to the wheels. All repairs to the brake line should be made with non-corrosive components designed for brake lines.
