Here are some potential reasons:
Air in the Brake Lines: If there is air trapped in the brake lines, it can cause a spongy or non-existent brake pedal. Bleeding the brakes is done to remove air from the system, so if there is still air after bleeding, it's possible that the bleeding procedure was not performed correctly or there may be a leak in the system.
Master Cylinder Failure: The master cylinder is a critical component of the brake system that generates the hydraulic pressure needed to activate the brakes. If the master cylinder fails or is damaged, it can lead to a loss of brake function. Signs of a failing master cylinder include a spongy or low brake pedal, brake fluid leaks, or brake fluid discoloration.
Brake Booster Failure: The brake booster is a vacuum-powered mechanism that assists the driver in applying brake pressure. If the brake booster fails, it can make the brake pedal feel hard or difficult to press, resulting in reduced or no braking power.
ABS (Anti-lock Braking System) Issues: While ABS is designed to improve braking performance and safety, there can be issues or malfunctions that affect the system's functionality. If there's a problem with the ABS module, sensors, or wiring, it can cause the brakes to behave abnormally, including a loss of braking power.
Proportioning Valve Issues: Some vehicles have a proportioning valve that distributes brake fluid pressure between the front and rear wheels. If the proportioning valve is malfunctioning, it can lead to uneven brake performance or a loss of braking in certain wheels.
Brake Line Leakage: If there's a leak in the brake lines or brake fluid hoses, brake fluid can escape from the system, leading to a loss of brake pressure and reduced braking effectiveness.
Failed Brake Calipers or Wheel Cylinders: The brake calipers or wheel cylinders are responsible for applying pressure to the brake pads or shoes against the rotors or drums. If these components fail or seize, they can prevent the brakes from engaging properly.
If you're experiencing no brakes when starting the car, it's important to have the vehicle inspected by a qualified mechanic to identify the root cause of the issue. Driving with compromised brakes can be dangerous, so it's crucial to have the problem diagnosed and repaired promptly.
