So I'm guessing you have discs on the front now?
In any case, the pedal needs to get hard, after the first inch or so, and not change much with multiple/rapid pedal strokes.
If the pedal gets hard without requiring at least about an inch if "freeplay",you have a C-port (compensating port) timing issue.
If the pedal travel is excessive, then you could have a different C-port issue or the rear shoes need adjusting.
If the pedal is not hard, but spongy, then you most likely have air in the system, or the front pads are not flat and parallel to the rotors
If the pedal does not get hard with multiple pumps, then the master may be defective.
If the pedal feels right but not quite right, then your front PADS may not be parallel to the rotors, or the rubber lines are ballooning.
There are different tests for each of these.
If the front brakes are dragging, then that again points to a compensating-port issue, or failing front hoses.
If the rear shoes are dragging, this points to an adjustment issue, a hose issue, or again, a C-port issue.
In all cases, there are only three sources of these issues, namely; hydraulic, mechanical, or adjustment.
In my plan of attack;
the first thing to go after, is to prove the master.
Then the rear shoe adjustment then, then the mechanical, and finally,the hydraulics.
If you do the hydraulics first, you may get a false positive and bleed for hours.
1) To test the master, simply put both feet on the pedal and push for 20 seconds. If the pedal does not sink, then there is a very high degree of probability that it is good. But if it sinks, with no external loss of fluid, then it is bad.
2) The rear shoes are supposed to be self adjusting.... as long as the correct adjuster is on the correct side! If you spend a lot of time backing up and slamming the brake pedal, they can become overly tight. In any case, you have to get the rear brakes working and adjusted right, to diagnose the rest of the system.
3) Next you can check that the calipers are functioning correctly, in that they apply and release immediately, with the pedal application, that they slide freely on their ways or pins, and that the pads are applying over their entire faces, and are not sprung on bent steel backers or wadded up noise insulators, or mountains of silicon.
4) after this, if everything checks out, it is time for a hydraulic test,
First a brief description of how it should work.
Inside the master are two fluid retaining pots, and two hydraulic chambers created by the piston assembly. The rearmost pot should be plumbed (in most cases) to the FRONT brakes, and the frontmost pot to the rear brakes.
When you press on the pedal, the two piston chambers are coupled together hydraulically and they move together as one.
At pedal application, the piston-stack slides forward. In the first 1/8" or so of piston travel, some of the fluid is forced back into the reservoirs. More on this later. The piston-pair continue until resistance in the rear brake circuit (at the front of the M/C) causes it to slow down. Then the rear piston starts sending fluid to the front calipers. After the line is thus charged, braking can begin.
After the stop is accomplished, the pedal retracts the piston assembly, and the caliper seals pull the pistons back a hair off the rotors, and the shoe return springs park the rear shoes. While all that is going on, the fluid returns to the M/C . As the pads and shoes wear,over time, if the C-ports were not there, the pedal would continually get lower, until no more stopping would occur. So the factory drilled those little holes in the bottom of the reservoirs to compensate for the sinking pedal, by always insuring that an adequate amount of fluid is in the system. If it should happen that the C-ports don't open, then the pedal will fall continuously over time. This can only happen if the rod that pushes on the piston-stack is too long, or the pedal does not return to it's proper parked position.
Ok, that's how it is supposed to work.
Now, knowing that; we can use the C-ports to diagnose the system. We know that the fluid has to return. And the quickest way to prove it is to look inside the M/C to see if it is. The proof, in a properly working system, will be a little roiling of the fluid. But if you get a little fountain, something is wrong. And if you get a geyser, something is Very wrong. So when you do this test, be forewarned, I have seen geysers spray fluid high enough to hit the underside of the hood, when multiple stroking was involved. If the previous tests were ok then you should not get a geyser. But if you have a lot of air in the system, multiple pumps will compress it; and when you release the pedal, all that compressed air can violently unload the fluid back to the master.
Special note
brake hoses usually rot from the inside out, and when they do, it seems they can make checkvalves inside the tiny tubes. So if your calipers are dragging,and you know it's not a sticking piston,then the way to prove that a hose is bad is to crack the bleeder. If fluid gushes out;the hose is likely bad. Yeah, the problem could be up the line, but not likely.
That's all I got
