I just picked up a 2001 Nissan Frontier. It sat for two years and The brake peddle goes to the floor. With the car off the peddle goes halfway then when I start it with the peddle held it goes all the way to the floor. I took the master off and there is no fluid coming out of it. What could be wrong with it?
There are internal seals that fail due to age, contaminated brake fluid, and rust.
A very common internal failure occurs when there is a loss of fluid and the pedal goes to the floor. The internal parts of the master cylinder have a build up of crud that the pushrod normally only goes up to that point...when the pedal goes to the floor, that point is passed, the crud ruins the seals and failure is imminent.
This easily happens even with simply bleeding the brakes.
Years and years ago it was common practice to rebuild them. Nowadays it is cheaper to simply install a new master cylinder.
For very old vehicles there are shops that disassemble, bore the cylinder, and insert a sleeve.
Your problem is likely air in the system or low pressure in the hydro boost setup that ties the power steering system to the brake system.
Master cylinders can be "bench bled" in or out of a vehicle...disconnect from vehicles lines, use fittings and place open end of tubing into reservoir, with fluid in reservoir, gently stroke pushrod in and out until no more tiny bubbles appear in reservoir. If you don't see fluid moving, master cylinder has failed internally. Then reassemble to vehicle lines and bleed rest of system.
Also problematic are the ABS control valves. It takes a computer hookup to cycle the valves. Air anywhere in a brake system is a problem...it won't go away on its on, has to be removed.
Sometimes its nearly impossible to bleed it all. That's where a pressure bleed is necessary. Harbor Freight sells one that works fine.