* Master Cylinder Failure: This is the most common cause. The master cylinder is the pump that builds pressure when you press the pedal. A leak internally or externally, or a damaged piston, will prevent it from building pressure.
* Brake Booster Failure: The booster uses engine vacuum to assist the master cylinder. A failing booster will result in a very hard pedal or no pedal at all, requiring significant force to stop the vehicle.
* Low Brake Fluid: Check your brake fluid reservoir immediately. Low fluid suggests a leak somewhere in the system (master cylinder, wheel cylinders, calipers, lines, hoses). Never top off brake fluid if you suspect a leak; find and fix the leak first.
* Leaking Wheel Cylinders or Calipers: These components are at the wheels and push the brake pads against the rotors (or drums). Leaks here will slowly deplete brake fluid and reduce braking effectiveness. You might notice brake fluid leaks around the wheels.
* Leaking Brake Lines or Hoses: Rusted or damaged brake lines and hoses can leak fluid, resulting in a loss of pressure. These are often overlooked but critical components.
* Air in the Brake Lines: Air in the brake lines is compressible, meaning it won't provide consistent pressure. This often happens after brake work.
* Proportioning Valve Issues (less likely but possible): This valve helps distribute braking force between the front and rear wheels. A malfunction can lead to reduced braking power.
What to Do:
1. DO NOT DRIVE THE VEHICLE. Driving with no brake pressure is extremely dangerous.
2. Check the brake fluid reservoir. Is it low? If so, there's definitely a leak somewhere. Don't add fluid yet.
3. Inspect the brake lines and hoses for any visible leaks or damage. Look around the wheels, master cylinder, and booster for fluid drips.
4. Have the vehicle towed to a qualified mechanic. Diagnosing and repairing brake problems requires expertise and specialized tools. Improper repair can lead to serious injury or death.
Ignoring this problem could lead to a serious accident. Get your brakes checked immediately by a professional.
