What is wrong if the car will stop but you have to press the brake pedeal all the way in?

Answer 1

Short answer: Most likely air in your brake lines which maybe be caused by a leak somewhere. Look up how to bleed your brakes if you are comfortable performing the work, or take it to someone who is. If its just air in the lines, bleeding them will solve the problem. (it would be good to track down WHY there is air in the lines, usually caused by a leak somewhere, or a bad brake master cylinder.)

Long answer:

If the car will stop, it means that at least some of your brakes are doing their job.

For some background knowledge, there are pretty much two types of brakes. They either squeeze or press outward on a metal disc or hub in order to slow the car down. I will use terms like disc and pads, but the same applies to hub and shoes.

It takes a good amount of force to stop the car, which is accomplished by hydraulic (fluid) pressure. When you press the brake pedal, the fluid is compressed in the brake lines, which, on the other end, where there is the ability to move, the pads are pressed against the disc.

What is most likely making your pedal "drop to the floor" is a leak or air in the brake system. Air is much more compressible that brake fluid, so when you press the pedal, you have to get all of that air compressed where normally there would be brake fluid. This takes much more pedal "travel" and will make your pedal move much more than normal.

You want to get the air out of your brake-lines, and make sure there aren't any leaks letting air in (if there are no leaks in any of the brake lines getting fluid all over your brakes, it may be the brake master cylinder).

Look up how to bleed your brakes if you are comfortable performing the work, or take it to someone who is. Again, try to track down how the air entered the system in the first place, and make sure you have enough brake fluid.