As for the "feel" of the brakes;
when you step on the brake pedal,
is the pedal high and hard? and does it remain hard?
If yes, then you do NOT have a hydraulic problem (besides slow leaks).
But
> If the pedal slowly drops, with no external leaks; then you have an internal problem in the M/C.
> If the pedal is low, give it a few quick stabs, then;
if the pedal comes up and is now hard, then you have one of two issues, either;
1) the rear brakes need adjusting, or
2) you have a mechanical fitment issue such as bent brake pads, oval drums, thin drums, squishy hoses, flexing calipers, or pads bent or not installed parallel to the rotors
But
if the pedal does not come up; most likely, the Compensating Port is not working. This port is in the M/C and the position of the piston that controls the working of it, is set by the length of the pushrod.
>If the system is working perfectly, including the pads contacting the rotors over their entire face; but the stopping distance is poor, the culprits might be, in order of likelihood;
1) the rear-shoes are not conforming to the drums
2) the friction material on your pads
3) It could be a pressure problem; and that is controlled by the size differential of the M/C bore to the caliper bore, or
4) it could be a pedal-ratio problem.
5) or, I suppose, it could it be the power of your brake-leg.
To find out which it is, you would have to rule them out one atta time
BTW
as to plumbing ;
the rear-most port on the M/C goes to the front brakes, via the end-port on the Combination Valve, which then splits left/right.
The front and rear braking systems are kept separated inside the Combination Valve. During operation, if one end experiences a sudden loss of fluid, there is a little shuttle valve inside the valve that moves towards the leaking end and turns the light on, on the dash.
<If the rear has failed, the rear-most split power-piston inside the M/C will move further on down the line than usual, until it hits the back of the front-most piston. It will then mechanically shove that front piston all the way to the bottom of the bore, where it will stay and shut off the fluid to the rear brakes. Then the rear-most piston will begin pushing fluid out to the calipers. The result of this, is a pedal that seems to go almost to the floor before anything happens.
But that is not all; when the brake pedal returns to it's upper, parking-stop, the inter-piston cavity is now much larger, and it has to be re-filled ..... thru the compensating port(s). and to do that, the pedal has to return all the way to the top, and to simultaneously PULL the rear-most piston back up. .... which means the pushrod has to be captured in the socket provided for that.
< if the front brake system has failed; the Rear-most piston again heads towards the front, same as usual, operating thru the hydraulic connection and the rear brakes do all the work. Two things manifest;
1) the rear brakes are only designed to do about 15% of the braking, so they are totally inadequate for flying solo. The stopping distance will be much increased, and it will take a lotta pedal pressure to achieve it. and
2) every time you step on the parked pedal, the rear-most piston may pump fluid out the leak, and eventually the reservoir will run dry. To mitigate this, you can just not let the pedal park, while you make your way to the repair shop.
But
from what I remember when I rebuilt my Combination valve, with the shuttle valve moved to either end of it's travel, that action also shut off the fluid flow from the M/C, to that end
3) remember, the front brakes are mathematically designed and hydraulically assisted to do 85% or more of the braking. The front hydraulic system has to receive 100% of the hydraulic pressure that your M/C is capable of generating at any one time, by your leg muscles, multiplied by the pedal ratio. This pressure can be as high as 1000 or more psi. But it all depends on the strength of your muscles. To make it easier on your leg, install a brake booster. They can easily multiply your leg-power in the range of, I'm guessing, 5>7 times.
The rear brakes are more or less just the automatic back-up emergency system....... altho it doesn't absolutely have to be this way.
The high and hard pedal is the desired end-goal, with a fully-functioning compensating port system, and the shuttle centered in the Combination Valve.
BTW-3
One of my favorite tests it to remove the calipers and shoes, then C-clamp all the pistons into their respective bores. Now step on the pedal which should almost instantly be ..... high and hard; and stabbing the pedal multiple times should make zero difference. A bit extreme? Well at 100 bucks an hour, I like to get to the bottom of things as quickly as possible, and this test can save a great deal of time spent in frustration. This test when it passes, completely exonerates the hydraulic system.
BTW-4
New shoes in machined drums, do not usually conform to them. If you look, they usually touch in only a tiny patch, close to the centers. Because of this, when the car is stopped, with brakes applied, those patches will force the drum to go oval and this then makes the drums act, like big powerful springs.
Firstly; This requires extra pedal-travel, with multiple stabs to achieve a somewhat hard pedal. and secondly during use, those little patches don't do much except act like expansion chambers to the front brakes, delaying and reducing their effectiveness.
If you see/experience this, you have two choices;
1) take your drums and shoes to an old-time brake shop and have the shoes cam-ground to fit the drums, or
2) get new un-machined drums, that may fit the shoes better ...... or not, you still gotta check them......
BTW-5
there are two flavors of shoes, those with long linings and those with short linings. The shorties go to towards the front of the car. This is for two reasons;
1) brake-drum systems are self energizing and the rear shoes do more work than the front, and so for equal life, the rear-most linings need to be a lil longer. and
2) if you reverse them, the long shoes, now on the front, will try to do the work, fail, and in the failing will reduce the effectiveness and life of the short shoes.
BTW-6
the parking brake strut that links the front and rear shoes, has to be relaxed otherwise rear brake action will be compromised. To relax it the Park-Brake System has to be adjusted. I know, I know; yur cables are probably seized. If they are, you need to fix that....... because sponginess in the rear brakes telegraphs into the effectiveness of the front brakes.
To test for this, just unhook the front cable from the splitter, then readjust the rear slack-adjusters to just tight enough to put a good drag on the drums. You may have to step on the pedal several times to center the shoes. Got High-hard pedal? BadaBoom!, fix the parking brake.
