My '67 Chevelle has brake problems. The car came with the brake problems when I bought it. Disc brakes front, drum brakes rear, with power brakes.

The brake pedal nearly goes to the floor. Pumping the brakes doesn't do much for it. The front calipers do grab the discs and stop them from turning. But the rear shoes do not expand at all when the brakes are applied. I checked with the drums off.

All brake lines are recently replaced. No leaks are evident at the rear wheel cylinders or the front calipers. There does seem to be a small drip between the master cylinder and booster. But the brake fluid does not seem to drop when the car is parked.

When bleeding the brakes, a powerful squirt of fluid comes out at the front wheels. Much less comes out at the back wheels - more like a dribble than a strong squirt.

Even after repeatedly bleeding the lines at all four wheels, there are no brakes in the back and the pedal remains very spongy.

I thought of replacing the master cylinder, but would rather not just start replacing parts without knowing what is causing the problem.

Any help will be appreciated!!

No brakes in the rear huh? I know you just said that all the brake lines were replaced. Any chance the rear line is kinked. Try this: first remove the rear brake line on the master cyl. and bleed the cyl till no more air bubbles. Is your proportioning valve ok? Meaning do you have good flow on the rear side of it? It's possible that your rear axle hose has deteriorated internally acting like a check vavle and restricting your fluid flow to the rear. Hope this helps.

The master cyl leaking in the rear is definately a problem. Replace it.

Possible:

Try a new master, do not be aggressive bench bleeding it. You can force the inner plunger in the master too far (before the air has escaped) and it gets stuck. Depress the punger 3/4's of the way. Once the mater is bench bled, you should bleed the lines going from the master. If they are good keep moving away from the master ensuring you are getting a strong spuirt.

If you have the old drum/drum distribution block, you need a disc/drim unit.

If you suspect the rubber lines are clogging or collapsing, replace them.

If you work from the master to thru each line you will find the problem.

how much of the stuff have you tried from your prior post on this problem?

did you find out if you have the proper proportioning valve?
and did you get a new mc?
and have you bench bled it?
are your rear brakes properly adjusted?
when you press the pedal and the lines are not hooked up are you getting fluid from both reservoirs?
just a few things to be checked and answered to get a better clue on how to help you with this problem
good luck