bad brakes after disassembly and reassembly

[sircrunch]

73 C-10 Power brakes, front disc, rear drum.... So here's the story. I did a complete suspension rebuild, new shocks, springs, bushings, you name it. Front and back. While doing this job I decided to pull everything and paint it all real nice, including the rear axle and front calipers.... everything. So I had to disconnect the brake lines front and back. I even put new brake hoses. So during this whole process which took me about 2 months off and on, the master cylinder leaked down. Fast forward a bit, I decided to rebuild the rear brakes, new wheel cyls, new shoes, new hardware. So when I'm finished I button everything up and bleed the brakes. It takes a while, but finally I'm able to get a good steady stream at all 4 wheels. I go for a test drive and its terrible. the pedal easily goes to the floor. The truck does stop eventually, but its very gradual. It would spell disaster to drive this truck anywhere except around the block. The pedal is very loose until it gets near the floor. If you pump the brakes, it does NOT get firmer, but instead stays sloppy.

At that point I decide to rebleed the brakes. I have spent a lot of time bleeding brakes. Again I get full force streams at all 4 wheels. There was no air coming out, it was good stream right from the start this 2nd time around. I try driving it again. It is no better than before....

At that point I raised the rear wheels and made good and sure that the drum brakes are adjusted right. They are snug against the drum.

At this point I raise all four corner and spin the wheels. All 4 wheels stop when brakes are applied.

So I'm here wondering what went wrong. The brakes worked perfect before I started this. The only reason I touched the brakes during this suspension rebuild is because 1) I had to pull the parts for repaint 2) the rear drum shoes were worn.

[Dead Parrot]

It is possible the master cylinder needs replacing now. When it leaked down, the piston moved to a part of the bore rarely visited. It was probably corroded there and damaged the piston seal. Your bleeding the brakes also visited that rarely used part of the bore. Better to have discovered it now then when towing your new boat home from the lake at 65mph on a 3 lane Interstate.

[Bandit130]

Yes, sounds like master cylinder. When I saw (the master cylinder leaked down) that was my first thought since I did not see that it was replaced in the list. Don't forget to bench bleed!!!
On the other hand, if master cylinder leaked down due to lines not connected to calipers/wheel cylinders, could have leaked down due to connections. Does not rule out master cylinder especially if it has been a few years since being replaced or if ever.