Soft Brakes

[Murfdawg]

I bought a 64 short bed step side at an auction. It was pretty thoroughly rebuilt by the PO. It has the CPP disk brake conversion with booster and stainless steel lines. Disk brakes in front and drums in rear with a proportioning valve.
It stops fine but has a soft pedal. So I thought bleeding the brakes was in order.
I am not a brake expert but have bled brakes numerous times over the years.
But this time I am puzzled and stumped.
I started with an assistant applying pressure while I cracked the bleeder screw. I GOT NO FLOW! This was with the left rear wheel. Since the brake lines are obviously near new I could not believe it was plugged and so tried all the other wheels. Same result, NO FLOW! I then tried a brake bleeder vacuum. NO FLOW!
I not only cracked the bleeder screw but turned it more than a full turn. NO FLOW! Each wheel cylinder is working just fine and the brakes work, but the pedal is soft.
Help please! Anybody have an idea what is going on? What am I doing wrong?

[Tazimafied]

Sounds like some gunk got in your brake lines or the fluid got contaminated somehow. I would take the entire system apart at this point, thoroughly flush it and clean out the master and slave cylinders.

[Captainfab]

It sounds to me like you need to re center the valve in the proportioning valve. It is most likely stopping the flow of brake fluid to the rear.

[Murfdawg]

Thanks Captain Fab, I was hoping it had something to do with the prop valve. I don't have a clue how to center it. Any tips? Thanks again!

[Rolland]

I recently rebuilt the brakes on my 60 GMC and had a similar problem.
Finally noticed that the bleeder hose wasn't fitting tightly enough over the bleeder screw nipple and was leaking air. Problem solved with a new and snugly fitting clear hose.

[Murfdawg]

I think I found the info I needed on the CPP website. I plan to work on it this weekend. Thanks for your help everyone!