69 Deuce brake problem Building pressure

Last sunday I did 120 miles in the duece. Went to a Veterans memorial hiway convoy run sporting flags along with 150-200 other rigs. I even won a first place ribbon even though other rigs were nicer. Doing a bumper to bumper convoy down a 40 mile hiway, I noticed eventually I had no power and a very high brake pedal. Turns out my brakes were dragging. On the off ramp I noticed smoke coming from all brakes. Pulled in to the stopping point and cracked a bleeder which let go about a 1/4 cup of brake fluid under pretty good pressure. Once the pressure was let off they no longer dragged and I was able to drive the trip home. My pedal is now about half when it shows pressure to stop. All brake components were rebuilt. Air pack, master cylinder and all wheel cylinders. The system was flushed with IPA and filled back up with dot 5 silicon fluid. The brakes worked very well for about 5 months. Now pedal is lower now (probably from shoe wear) and I'm pondering what would create the excess pressure I had to release. Could the air pack have a bad valve or something?? Master no returning before my next push on the brakes? What do you guys think?.... Al

KJ;
Sounds to me like a tiny leak from the air side to the hydro side. It doesn't take much to happen either. Re-check the Master Cylinder to be sure no leak is there, but I'll bet it is.

Sounds like time to rebuild the air pack. They go out two ways...either your brakes stick like yours did...or no brakes at all!! The air packs are simple to rebuild, having the manual handy is not a bad idea though. Pictures are worth a thousand words sometimes!
On the air pack, facing the rear of the truck is a 1/8" NPT pipe plug (often hidden by layers of paint, grease, mud or a combination). Evvery so often you should remove this pipe plug and squirt in a few drops of light lubrication oil, this "should" prevent this from happening again. This is a lube point that is overlooked more often than not on these trucks.

Good point DS, I forgot about that. (Overlook pun intended<img src="emoticons/icon_smile_lol.gif" alt="LOL">)

Absolutely everything was rebuilt approx 5-6 months ago. I did the air pack with the help of the manual. They worked well through all that time. Some freeway miles and it acted up...

KJ;
You have my sympathies! In my 1.5 million miles of driving/repairing diesels I've learned when you shake down a system rust and impurities let loose and can bring havoc to a new and beautiful reman or rebuild. It doesn't take much to put a pinhole in a piece of rubber or plastic and rain on your parade (sorry, can't resist the puns). When she's out on the highway, she's at full tilt and you're actually finding out where the weakest link is when she's at max. power. Just be patient and go through the air pack again and see if there is a leak because by the way you are writing it sounds to me like that's the problem. These air packs are very tempermental and incredibly sensitive to any kind of debris in their system. Keep us updated. If it's something else I'd love to know and build upon what I already understand.