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The axle change will not solve your problem as the brake hydraulics are unrelated to things like which size birfield or full floating/semi floating axles, knuckles, etc. The problem MUST be somewhere between the brake foot pedal and the furthest wheel cylinder (right rear) in the system and be contained therein.
If the pedal goes to the floor repeatedly and CAN NOT be pumped up you have a leak. This could be internal i.e. - brake fluid is squeezing past a seal in the master cylinder and thus the master is not pressurizing OR your leak is external i.e. - fluid is escaping the system such as squirting out a loose bleeder or damaged line (hard or soft) or past a wheel cylinder where you will eventually see it on the ground. You would see a noticeable drop in the reservoir (front or rear) after half a dozen pedal depressions (unrelated to "Non-Functioning Cruiser Depression").
If the pedal goes to the floor on the first pump but repeated pumping increases pedal pressure that DOES NOT diminish as you hold the pedal down on the last pump you have air in the system. Period. Fluid is used in hydraulic systems because, unlike gas (air), fluid is difficult to compress. An air bubble in a closed hydraulic system will eventually compress and allow a modicum of service UNTIL you release pressure and the air expands again at which time you will need to re-apply pressure (pump your pedal) until the air is compressed enough to force fluid thru the lines.
If the pedal goes to the floor until you pump it up it and then, after re-establishing pressure, the pedal slowly goes to the floor while continuing to hold it down - you have a slow leak either internal or external.
Two further points:
1} Any contamination to the system from conventional petrochemical compounds will cause hydraulic seal failure. And dang fast, too. Is it possible you inadvertently used the wrong type of assembly lube when installing your new components? Grease on your hands? Did you blow out the hard lines with brake cleaner?
2) A hole or leak in a hard or soft line can exhibit a one way effect at times. Fluid may not leave the system with the application of pedal pressure but air may enter the system as pressure is relieved (foot off the pedal). The air is sucked in thru the hole as pressure drops. This is uncommon but I've known it to happen. A poorly fitting connection at any point in the system can contribute to this affect. Whether you would see a rising fluid level in your reservoir or not is dependent on how much air is entering the system and contributing to system volume. Air may be drawn into your system as the pedal moves up and be expelled as pressure is applied as well. Fluid can also be forced past a leaking wheel cylinder seal, collect under the dust cap, and then be re-drawn into the system. You'd eventually see a visible leak due to the fact that the wheel cylinder dust cap is not designed to hold any pressure. Look at the inside of your bleeder valves. Are there any nicks/gouges or are they shaped irregularly. They must make a perfect metal-to-metal seal or you will have problems.
I am a little unhappy with your description of bleeding the system with your brothers help. The brake bleed valve at each wheel cylinder should be closed firmly until pressure is applied to the system (your brother's foot on the pedal). This need not be excessive. Then open the valve. Fluid/air will be forced out of the bleed valve and pressure will begin to diminish (leak). YOU MUST CLOSE THE BLEED VALVE BEFORE ALL PRESSURE IS LOST OR AIR WILL RE-ENTER THE SYSTEM. Sorry for the emphasis. The volume of fluid moving thru the system displaces air better than high pressure. If your assistant's foot bottoms out it can prove too late and air can re-enter the system before you close it off. Close the valve as the fluid is still squirting from the bleed screw hole and begins to tail off. You only need to turn the bleed screw about a half turn (or less) either way. If his foot comes off the pedal or he raises his foot so much as a millimeter or two you will doomed to a never ending cycle of air contamination.
Here's what I would do. Re-check all connections for tightness. Confirm that your hard and soft lines are in perfect working condition. Be honest about your sterility level when assembling your system and then diagnose either a LEAK or AIR IN THE SYSTEM. I'd hate to see you spend a lot of money and effort and end up with the same problems all over again. Once you get your brake skills in order it will matter little whether you're working on a disc or drum system or whether or not it's boosted. HTH
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