spongy brakes.... im at a loss...

Ok so here is the full length story. i have a 76 f250. dana 60 rear and dana 44hd front. i had all the componts for brakes replaced in the rear, wheel cylinders, drums, hardware, and shoes. all the rubber lines going to both front calipers and the single line going to the rear diff. calipers have been replaced a few years ago. master cylinder and power booster since the rear brakes were done. this was not a married unit. i adjusted the nipple on the booster to meet the master cylinder so that the cylinder sat flush to the booster. according to my haynes book on their is a bleeder rod on the pressure differential valve that needs pushed in, in order to bleed the calipers. due to gvwr is over 6800lbs. With the truck shut off the pedal has about an inch of freeplay and feels like it should. with the truck running its spongy and travels almost to the floor but the brakes work like they should but way more travel than they did. ive tried bleeding in every which way that i know as a mechanic and as the haynes book says but the pedal doesnt feel right. there is for surely no air in the system and no signs of a hydraulic leak anywhere.... any ideas? neighbor says maybe the reman booster is defective or "works" too good? also there are no adubile vacuum leaks, thats why i changed the booster. The master cylinder is new and not a reman.... HELP!!!!!

It sounds like the rear brakes need adjusting.
Too much freeplay between the brake shoes and the drums can feel like air in the system

This one had me thinking, but I think echnidna may have hit the nail on the head!!!
Kurt

Back it up and apply brakes several times----unless they left out the self adjusting hardware--------

Make sure the front caliper slides are not froze up,along with the other suggestions. Also when doing rear brake jobs you need to be sure the e brake adjustment is backed off before you do main adjustment,then go back and re adjust the e-brake.

If it's spongy, I'd suspect the hose(s). Maybe you could have someone push the pedal down and release while you held the hose and see if you can feel it expand..??..?? Do them one at a time. Simple check and cheap too! I don't care how "new" they are, we've all had a defect or two right out of the box!