If the brake booster is bad, then you need to apply a large amount of force for the master cylinder to pump the pressurize brake fluid down the system. This means the brake pedal might have to travel downward beyond its normal throw and you might find the brake pedal goes to floor.
How do you fix a brake pedal to go to the floor?
How do I know if my brake master cylinder is bad?
Is it safe to drive with a soft brake pedal?
If your brake pedal feels soft or 'spongy' stop immediately and get a breakdown mechanic to check the car. Driving with a 'soft' brake pedal is extremely dangerous because your brakes could fail at any moment, even if they don't fail they will be inefficient, possibly leading to an accident.
Related Question What does it mean when my brake pedal goes to the floor?
Why would my brakes lose pressure?
This can be due to a number of problems: a leak in a brake line, a loss of pressure within the master cylinder itself due to a failed seal, or air being introduced into the braking system. Your first reaction to encountering spongy brakes should be to rapidly pump the brake pedal with your foot.
Is it safe to drive a car with leaking brake fluid?
Brake systems in today's vehicles are activated by brake fluid, so keeping enough brake fluid in your vehicle is imperative to ensure the safety of you and your family – brake fluid leaks are the most common cause of total brake failure, and you should not drive a vehicle that is leaking brake fluid.
Can a bad brake caliper cause soft pedal?
If the caliper is leaking, it can cause the brake pedal to be extremely low or go to the floor.