1968 break pedal issues

[Heathcliff68f100]

My 68 ford needed major break work when i got it,
new rear drums,
new spring kits,
new wheel cylinders all around,
and 2 new master cylinders,

Isaid 2 because the first one sprang a leak at the rear seal,
the second one, the one thats currently in it, has a "spongy" feel.
the pedal, is pathetic, push once, it builds up pressure, let off, push again, and firm as can be. but let it sit, and push the pedal, and it goes to the floor, nothing happens, ive bleed the brakes hundreds of times, HELP i need to figgure this out so i can drive this bad boy..
Thanks

[fordman]

sounds like a bad master still. my 67 does that. i need to replace the master.

[Heathcliff68f100]

Theres nothing else that could cause this problem?, it couldnt the the porportioning valve? Is there any chance i would need to pressure bleed the system?

[91Bear]

It's a brake pedal, not a break pedal.

[fordman]

these drum brake truck only have a pressure differential switch in them. that switch trips when it gets a low brake fluid pressure in either the front or back brakes. and all it will do is turn on a light on the dash. if the switch was tripped it would make the brakes bad all the time.

[Heathcliff68f100]

so if my differential switch has been tripped, it would affect my brakes all the time?
sorry for so manny questions, but, how exactly does this switch work?

[fordman]

let me start over here. there are a many things that can happen to make the brakes spongy. with new drums and old shoes the shoes may not be completely touching the drums when the brakes are applied. rearching the old shoes to match the new drums is the correct procedure for replacing drums. if old shoes are used they can be worn to a point where the wheel cylinder can reach the end of the correct travel for it before it comes apart and could leak out fluid. and not correctly apply the brakes. on the overextended wheel cylinder. a leak in the lines could also make this happen. the centering of the differential swithc has to be done when bleeding brakes. you do it similar to bleeding the brakes. one person pushes on the brakes as you loosen up the switch and then retighten it. this will reset or center the pressure in the lines correctly. other things that can happen is there master can bleed back internally to itself. the symptoms you are describing are the symptoms of a bad master cylinder though or a leak in the system someplace. that is what i am reading anyway. if it was just spongy and didnt bleed off then it could be one of the other things mentioned. maybe one of the wheel cylinders isnt all the way tight or seated into the wheel cylinder.

[Heathcliff68f100]

Well, that all makes sence, but i believe my brother inlaw and i found the problem, the adjuster on the rear passenger side drum wasnt adjusted properly and loosened itself, i reinstalled it, and adjusted it, and now the pedal is MUCH better, Thanks alot for the help, i really appreciate it