Brake pedal sometimes goes to the floor

Question

I am a new driver and for a couple of days when I press the brake pedal, sometimes it sinks to the floor to stop. It usually happens after driving a few miles without braking but sometimes it happens right after starting the car and moving. We replaced the brake calipers and pads and bled the air out of the lines a few times with the mechanic and he confirms that there is no problem in the master cylinder and ABS module and there is no any leak on the hoses as well. But one of the rear rotors turned a little purple and he said it could be the cause for sinking and telling me try driving the car for a couple of weeks and the problem may go away. Replacing the rotor could clearly clarify if the issue is with the rotor, but replacing everything to find the problem is so costly and I am student. Cloud it really be the rotor that causing the brake pedal sink sometimes but not always? It seems really dangerous to drive for weeks like this as you don’t know when it works properly or fails.

Answer 1

A few possibilities. But you should never keep driving a car hoping brake problems go away. They don't and it's dangerous. There is a cause for this problem, and it can be fixed. The place to start is the blue rotor. It is overheating. The cause for this is usually sticking slides, faulty caliper or a bad brake hose not allowing the calipers to release pressure on the pads. Depending on the age and condition of the vehicle the overheating of this wheel could cause the water contaminated brake fluid to boil causing your symptoms. So first you need to resolve this wheels problems. Then when all wheels are functioning properly the system needs bled properly. This should also include an ABS bleed. With all four wheels working and all air removed with good brake fluid, the only thing that could cause this is air in your master cylinder or a faulty master cylinder. I realize that your mechanic confirmed these things were good, but frankly, a mechanic that tells you to keep driving on faulty brakes in hopes that it gets better is not trustworthy to confirm such things. You really should find another mechanic. You say you can not afford to do much, but you definitely can't afford driving without good brakes.