- Brake fluid leak: Check the brake fluid level in the reservoir. If the level is low, there is probably a leak in the brake system, which needs to be found and repaired. Common leak areas include:
- Brake lines (usually occur due to collision or extreme rust damage)
- Master cylinder
- Wheel cylinder
- Brake caliper
- Faulty brake master cylinder: The brake master cylinder is responsible for creating the pressure that forces brake fluid through the brake lines. If the master cylinder is faulty, it will not be able to generate enough pressure, which will cause the brake pedal to go to the floor. Some signs of a faulty master cylinder are:
- Brake fluid leaking from the master cylinder
- Soft or spongy brake pedal
- Brake pedal goes to the floor
- Faulty vacuum booster: The vacuum booster is responsible for assisting the driver with the effort to press the brake pedal. It uses the engine's vacuum to multiply the driver's force on the brake pedal. If the vacuum booster is defective, the driver will have to press the brake pedal much harder than normal in order to stop the vehicle. Some signs of a faulty vacuum booster include:
- Hissing or grunting sound when pressing the brake pedal
- Brake pedal feels hard or difficult to press
- Brake pedal goes to the floor
- Faulty proportioning valve: The proportioning valve is responsible for distributing brake fluid to the front and rear brakes. It is designed to provide a balance of braking force between the front and rear brakes. If the proportioning valve is defective, too much or too little brake fluid may be sent to the front or rear brakes, which will cause the brake pedal to go to the floor. Some signs of a faulty proportioning valve include:
- Uneven brake wear
- Front or rear brakes locking up
- Vehicle pulling to one side when braking
Repairs:
- Replace the brake master cylinder: If you think your master cylinder is faulty, you will need to replace it. This is a relatively simple and straightforward repair that can be done in about an hour.
- Replace the vacuum booster: If you think your vacuum booster is faulty, you will need to replace it. This is a more difficult and time-consuming repair that will require removing the brake master cylinder and the entire vacuum booster assembly.
- Adjust the proportioning valve: If you think your proportioning valve is faulty, you can try adjusting it. Instructions on how to do this can be found in the vehicle's repair manual. If the proportioning valve is not adjustable, you will need to replace it.
