The hydraulic part of your brakes uses two kinds of plumbing to carry fluid from the master cylinder to the wheels: rigid brake lines and flexible brake hoses. They do the same job in different spots, and they fail in different ways.
Brake lines: the rigid metal runs
Brake lines are hard metal tubing - usually steel - that carries fluid along the frame and body where nothing moves. Being rigid and strong, they handle high pressure well and last a long time, but they can corrode from road salt over the years, especially underneath the car. A rusted-through line will leak and must be replaced. Browse brake lines.
Brake hoses: the flexible links
Brake hoses are flexible rubber (often reinforced) that connect the rigid lines to the moving parts - mainly at each wheel, where the suspension and steering move the caliper relative to the body. Flexibility is exactly what is needed there, but rubber ages: it can crack, bulge, or collapse internally over time. Browse brake hoses.
Why a bad hose is sneaky
A hose can fail on the inside where you cannot see it. A collapsing hose can act like a one-way valve - letting pressure to the caliper but not releasing it - which makes a brake drag or the car pull, much like a sticking caliper. A bulging hose under pressure wastes pedal effort and gives a soft feel.
Signs to replace
- Cracks, bulges, or chafing visible on a hose.
- Wet spots or corrosion along a metal line.
- A brake that drags or a car that pulls under braking.
- A soft pedal with no other cause - see spongy pedal causes.
Lines and hoses are safety-critical and hold high pressure. Any leak means the vehicle should not be driven until it is repaired. When in doubt, have a professional inspect the system.