[LordNatedawg]

Vented my frustrations, read through CPPs troubleshooting sheet, and then did some research on braking systems.

Here's what I came up with:

After looking at old part numbers (**** glad I documented part #s), it appears that I ordered a MC and brake booster kit for a 1/2-ton truck. Meaning the bore of the MC is too small to push out the required volume of fluid needed for 3/4-ton disc brakes. It explains why my pedal has a good amount of resistance, but goes to the floor. The MC is currently producing pressure, but not volume.

The bore I have on my MC is likely 1" or 1-1/8". The solution is grab a MC and proportioning valve off of a 1979 GMC 3/4-ton (to match the front discs). They used a 1-1/4" bore. This will allow me to meet the volume needs of the heavy duty disc brakes.

Essentially what we're looking at is the difference between JB5, JB6 and JB7 braking systems. JB5 systems are on light duty 1/2-tons (your typical GMC 1000 or Ch*vy C10). JB6 systems are on heavy duty 1/2-ton and light duty 3/4-ton. JB7 is for light duty 1-ton and heavy duty 3/4-ton. I mixed and matched JB5, JB6 and JB7 parts. My truck has a GVWR of 7,500 which would put it in the JB7 category (7,500-8,400).

So, I'll be ordering a new master cylinder for a JB7 system and I'll see where that gets me. Probably a new proportioning valve too, just to be on the safe side.

*This post is a compilation of everything I researched today. It is accurate to the best of my knowledge.*