Failing at bleeding the brakes

[Loa]

Hello,

One of my brake cylinders (in 73 mopar) in the back wheels died and the brake fluid leaked out during the night two days ago. I got two new cylinders and installed them without issue. I refilled the master cylinder's smaller reservoir with brake fluid and bleeded the two lines to the back of the car. Everything went fine and was normal.

For good measure I decided to check the front lines (which had been working fine). And that's when I found my problem. They just can't be bled, there's always air. Lots of it. I've bled each line about 15 times (always making sure not to empty the reservoir) and by the time I stopped, the fluid was foamy!

I checked under the car and there was no leak, nothing. Air is coming in from somewhere, but I don't know where.

Any tips?

Thanks.

[Bullitt-]

When using a hand held vacuum pump pump once I experienced this & found I had loosened the bleeder to much.
Otherwise I would be suspicious of the master cylinder...

[Loa]

Could the same problem occur with the old fashioned method of pumping the brake? I may have opened them too much.

[jimynick]

Start from scratch. Go to the rt rear wheel and after topping the MC, loosen the bleeder a quarter turn and wait until the fluid leaks out, close the bleeder, go to the lft rear and do the same thing and then the rt frt and lft frt respectively, making sure the MC does not run low all the time. I'd then enlist a friend and go back to the rt rear and crack the bleeder while buddy slowly depresses the pedal. If you squeeze a chunk of appropriately sized clear plastic tubing over the bleeder nipple, you can put it into an old water bottle with a 1/2" of fluid in it and watch when the brakes are pumped to make sure no air bubbles are in the last pump and by keeping the end of the hose under the fluid, there's no chance of sucking air back into the system. Do that on all four corners and if, as you say, there's no leaks and you still haven't got a decent pedal, it's likely, as mentioned, in the MC itself. Good luck. 

[Loa]

Just a quick update: I brought the car to my local mechanic (who knows his way around classic cars) and not only is the MC broken, but the booster as well...

Sucks, but at least once it's done I'll have completely new brakes (given that I had changed the front callipers, discs and pads last year).

Thanks for the help.