i was driving home today and i steped on the brakes and the pedal went all the way to the floor. i havnt done any work on the brakes so i know there is no air in the system. they where working fine yesterday. the resvoir is full of fluid. no leaks on any of the lines. i just wanted to get some input before i start buying stuff. could it be that the master cylinder is bad?

 

Master cylinder might be the problem
OR
you have a leak in the system (common for rear drum to fail - old cars!)

 

need to change the piston in MC

 

I agree, had the same problem. A new MC will fix that.

 

yeah i pumped the brakes with the car off as if i would bleed the brakes it makes this like weird buzzing sound when it is releaseing the pressure and even after pumping the brakes the pedal still goes straight to the floor. since the mc might be the case i have been wanting to upgrade and have access to a DA. is it even an upgrade to us the da brake booster and mc, will it fit?

 

Highly debatable.

You get a larger bore MC which is able to push more fluid out to the wheels.
Sounds like an upgrade - BUT - since you are still using stock brakes all that is going to happen is that you will not have to press the pedal down as far as you normally would have to for the same amount of braking.
Still sounds a bit like an upgrade - BUT - the reduced pedal travel reduces the distance you need to press down to lock up the brakes and skid... which is bad. If the MC was HUGE and you only had to 1/2 inch of pedal travel before it would lock the wheels then stopping the car properly would be extremely difficult. No, the DA stuff won't make it THAT bad, but I exaggerated it to give the image to consider.
In tight situations or in racing you want the some travel so you can modulate the brakes for efficient braking and avoid skidding.

Upgrade to the DA knuckles and calipers up front and discs in the back (along with the 40/40 proportioning valve) and you will be braking just like it was designed to.

 

Buzzing sound is coming from the engine bay, right?
That would be fluid rushing past the failed seal inside the MC.

 

i suggest to get a brake repair kit and you dont need to replace the MC!

 

i got a new MC for 44$ and maybe check to see if ur 2 lines that come out of the MC are broken, cracked etc.

 

not exactly..

Mine are both stripped and beat up as hell and still seal everytime those done usually break , at least not in my experience

Honestly I just had the same problem , 75 buck alter still no brakes , evenw tih a new MC , Check and see if fluid is coming out of the rear drums anywhere , I had a blown wheel cylinders on both sides