...The pedal always felt good and the brakes felt fine for normal driving. But when I safely tested their ability, I learned they didn’t have much more stopping power than I had been using.
Then it's very unlikely you need to continue to bleed them. Air in the system will make the pedal more "soft" or "spongy" feeling. If it's full and firm, air is not the issue to my mind.
This could be due to a weak vacuum booster. Or maybe even a weak vacuum signal if you have a performance cam or leak or something like that.
But a weak booster is not uncommon. Is it new, used, older new, or original factory style?
Hard to tell probably if you didn't install it yourself, and they were not available on the actual truck until near '76 if I remember.
I replaced one of the axle seals and did not notice anything out of the ordinary. I am familiar with drum brakes, but with the leak in seal possibly contaminating the rear shoes on one side, even though they looked fine, I will replace them.
I'm not sure I'd bother just yet. If they don't look contaminated (and you're familiar with how they should look) it seems a waste of time unless you think you can get a better friction material. Sometimes the compound alone can make or break how the system works.
Especially if your testing was done cold.
Any ideas on what vehicle the master would have been found on would be helpful but i imagine I will need some pics before anyone can id it.
Correct. Way too many possibilities.
If it's got equal-sized reservoirs and two wire bails (the top clamps) then it's likely the aftermarket replacements like we sell, or perhaps a used GM-based setup.
The diameter of the piston is critical. I prefer 1" but you can go as large as 1 1/8" with these setups. But not larger until you get into hydro-boost systems.
If it's got an odd-shaped top, with one large reservoir in the back and a much smaller one in the front, with a single wire-bail that flips up from the sides, it's likely Ford-based.
But even the factory Ford drum brake master is perfectly fine for front discs. That's the setup I have and I can lock up both front and rear with 32" tires.
But that leads to another question. With 33's you really need as much performance as you can get. From shoe and pad material, to booster strength.
First thing I would do is peek over the tops of the front tires and make sure you see daylight (or the ground) between the calipers and the steering knuckle castings. If not, you need to do some grinding. If there is some, best to be at least 1/8" or so for pad wear. A little more might be even better.
The booster-to-master rod clearance sounds ok. If it was not, you would either have a longer pedal travel than normal (too much gap) or your brakes would start dragging after awhile (no clearance), but it sounds like you don't have either issue at this point.
Also, can you tell what size rear brakes you have? Small ones would be 10" or so, and the large ones were 11" or so. In '72 (assuming the rear end and brakes are still from the '72) a large brake would have meant a large bearing axle. If you remember the part number of the seal you bought, that can tell us whether you have large or small brakes.
If the small brakes, then maybe you're fighting more uphill with the heavy 33" tires as well.
So there are still some diagnostic tests you'll need to be doing to see where the weakness lies.
Paul