i replaced both of my calipers and i bled the brakes. with the car off i had a stiff pedal. when i started the engine,and pressed the brake pedal it goes right to the floor what could this problem be?

The brake system is not building pressure for some reason, and you'll need to look everything over to determine why. I would check all the brake lines and connections again, and also make sure the brake fluid is full, and didn't empty filling the calipers.

You may wish to try bleeding again if nothing is obvious, being sure to keep tabs on fluid level. Bleeding should hopefully give you an idea what'* going on. Unless your brake booster magically decided it wasn't doing enough to help you with the brakes, and cranked the assist up to 11, but that would be apparent when you try and bleed the brakes, because it will be making ALL the pressure.

If the wheel brake cylinders have all been properly bled, and the fluid is up to the correct level, you need a new master cylinder.

If you had no problem before the brake work, chances are it'* air in the system....especially, as someone mentioned, if you allowed the fluid level in the M/C to drop too low while doing the work....

It'* also possible, you may have air trapped in the ABS modulator.....

Hi Amallin1, Sometimes with an old master cylinder when bleeding brakes when the pedal travels out of its normal range of motion it can cause the master cylinder to fail, eating seals or whatnot. I agree you should probably replace the master cylinder, then when bleeding again make sure you move pedal slowly both ways, never let the reservoir go dry, and (opinions seem to vary on this so here'* mine: ) push the brake pedal to about an inch before the end of its travel.

Let us know how it goes!