What is wrong with the brakes on my 93 cadillac deville?

93 cadillac deville 160K miles, 4.9L V8 w/abs. I missed a turn and hit the brake kinda hard.the tires squeaked for about a second then the pedal sunk to the floor and was much weaker. The brake light is on (parking brake is off). Now to stop the pedal has to be pushed in quite a ways and are weaker. I looked a the brake fluid tank and it was low. So i added so dot3 fluid. the brake light went off for a while. the brakes still felt the same though. I drove around a little and the brake light came back on and the fluid in the tank is nearly back to where it was. I was going to take the front wheels off and inspect the brake and lines. any suggestions? what should I be looking for?|||Couple of suggestions,one would be to get underneath and have some one pump brakes to check for leaks you might have to llok from front to back checking the line as you go.Also look around master cylinder and check the lines around that area MAKE SURE YOU BLOCK THE WHEELS TO KEEP IT FROM ROLLING.If yoy dont find any leaks you may have gotten air n your line if you know how to bleed the lines you might try this,these are a couple of things that I would try ,but you may have to take it to a mechanic.|||Sounds like you got air into the brake lines when you stomped on the brakes too hard. Would almost suspect bad master cylinder, but, you may need to have all the brakes bled, to get the air out of the brake lines. If that doesn't cure the problem, then you'd need to replace that master cylinder. Good luck.|||Sounds like one or more of your brake wheel cylinders is leaking. Get it to a proper brake service mechanic as soon as possible, and have it repaired!|||the second guy got it right its mostly a busted wheel cylinder dont waste your time taking off the front wheels just look under the car at the back wheels if the wheel cylinder is leaking you will see fluid on the tires