I have seen the above problems so often its not funny,
& its not funny..
Heres whats happening...
Brake fluid is hydroscopic, if you paid attention in science class, that means it 'Absorbs water'.
So if the brake fluid has absorbed water & the master cylinder is iron, then the master cylinder is going to rust inside it.
Now once its started to rust in the bore, the wee piston thing will push any rust particals down the bore.
Where the piston stroke stops is where the rust particals will stop & sit.
Once they sit there they will form rust pits in the bore, & rusty lumps on them.
Now what happens when you go to bleed the brakes is you push the piston past its normal travel.
The seals hit the rust & pick it up & it gets into the brake fluid.
Its also just stuffed the seals.....
Thats why when you push hard on the pedal after bleeding the brakes, its sinks slowly to the floor.....
And why, when bleeding the brakes, theres dirt (rust) in the fluid long past where the clean fluid should have come out.
A good garage uses vacuum to actually 'suck' the brake fluid thru the system.
They put a small delivary devise on the open master cylinder & when the fluid drops past a certain amount, it tops it up again, less air gets in the system that way & its now a one person job.
They also use a different colour so they know when its been evacuated of the old fluid.
The answer?
Clean out the master cylinder of all rust, clean everything else in it.
{ Or just get a reconditioned one....
They bore a old one out & put a stainless steel sleave inside it.
They also put some special grease on the seals & from what they told me, it will "last forever".
Cost me $125 NZ (US$60) for a car one 13 years ago, saved me heaps...}
Replace the seals, put in new brake fluid (new. Not stuff thats been sitting around for years absorbing water from the air) & bleed the brakes again,
using vacuum if you have it (some people have little hand vacuum pumps for doing jobs like this)
or just use the pedal again & try not to go past where the piston would normally travel.
The first poster ^ probaly got it right thru persiverance.
But THATS whats happening.
I think someone with a few tools could make a bit of money one the side knowing all this.
You can make a electric vacuum pump from a old refridgerator pump, thats probably within the abilitys of most people here, theres plans on the net about how to do this, it mostly involves getting the wiring right & then also the correct hoses on the pump & a little bit about lubricating it as well.
They last for a while & then stop working right, but by then you know how to make another anyway.
Hows that for a post?
.....