Problem with brakes...

Hi,
i had bought an APV 90's with 3,1 L engine.
The problem what is is that i have no brakes, just the parking brake is working, i have no pressure when i press the brake pedal.
When i pump 3 or 5 times on pedal i have a little bit presure but when i released the the pedal for 3 seconds is the thame problem beginning, when i hold the pedal the presure is in same position.

So my question is, is it the brake booster or the master cylinder?
The brake fluid is made new for 2 years, and no leak is in the system is enough fluid in reserviator.

Failed master cylinder is the likely cause...in fact I do not see what else it could be....unless some work was done on brake system and it was not bled properly. IF brake booster was involved, pedal would be really hard to depress.
Failed master cylinder is a rather common occurrence at that age.

So i have overhauled my old master cylinder, and where i put the old brake fluid out of the master cylinder there was black thinks in the fluid.
The rest was in normal color, but there was something like black slam in fluid, can it be that was the old seal? Was it normal?

IF you have bought it recently, the previous owner may have poured incompatible fluid type that dissolved the seals or pistons. WHen my son bought a Z34 2 years ago, the previous owner had poured transmission fluid in the master cylinder..with about same results as what you describe.

Ok, so can it come from DOT4? I think the Master Cylinder seals was the original, I have made all in the cylinder new can it come back when i used DOT 4?

ALl I read says dot 4 and dot 3 are compatible.
http://answers.yahoo.com/question/index?qid=20080224225031AAyZAcx
as well as a lot of other links
I've used dot4 in my '93, and also after changing master cylinder for son's '92 Z-34
New parts produced for rebuilding MC are surely built to recent standards anyway.
dot5 needs more specific seals and pistons though.