Technical 40 Ford Brake Problem

I'm working on a 40 Ford with disc brakes in front and a Ford Exploria disc brakes on the rear. I installed a CPP below the floor power master cylinder kit. I installed a 2lb check valves to the front and rear. I also installed an adjustable proportional valve for the rear after the check valve. I bled the brakes including bench bleed the master many times, but still seems like I'm getting air bubbles. FYI, I'm using a vacuum bleeder. The pedal and rod that goes to the master has the correct clearance.. I have brakes and it stops all 4 wheels, but it's a low pedal, and it doesn't return to the top. I have th pull the pedal up with my foot to release the brakes. This is the first time working on below the floor master cylinder..
I'm stumped, any help would be appreciated.

 

Put a good return spring on your Pedal first off. Low pedal compared to what? (pedal ratio plays a part)
Go drive it, you'll find it may stop just fine without going to the hard spot with it just sitting still.
The Wizzard

 

Putting a vacuum hose on a wheel cylinder bleeder will bleed the cylinder, BUT, it can allow air in also around the threads of the bleeder, giving the appearance of air in the cylinder. This is especially true with new stuff, not so much with older stuff. X2 on return spring. Bones

 

Since your pedal isn't coming all the way back up every time, you may not be letting the cylinder refill at rest.

 

Your booster also has a clearance requirement to the master cylinder. Those small dual diaphragm boosters can get mighty warm under a 40, with the added engine heat the rubber is a little more pliable, so you may need a little extra clearance just to get the proper clearance if that makes any sense to you.
Quik test: Loosen your M/C at the booster and put a couple of 1/16-1/8 body shims and retighten and see if it improves any.

 

Adding a pedal return spring (as already mentioned by alchemy) is very important because the booster internal spring is not designed to return pedals and linkage. In addition;
1-Make sure the pedal is completely free to full travel when dis-connected from the booster.
2-Check for full booster return by making sure the pedal can continue moving back when disconnected from the booster.
3-The clearance between the booster output rod and master cylinder primary piston is critical, and usually around .040" unless otherwise specified, and this should be checked with about 20"Hg vacuum applied.
4-The master cylinder should be able to fully stroke (open circuits) before the pedal bottoms out, to utilize the safety advantage of a dual master cylinder.
5-Using the stock '40 pedal with it's approx. 6:1 manual ratio may be too much for your booster, as most power pedal ratios are in the 3-4:1 range.

 

I'm dealing with the exact same set-up in my '40 pickup. I bled the brakes 4 times and the pedal still seemed to go almost to the floor.
I've double checked the shims in the front disk. They were all good.
I changed the vacuum line for the booster and that helped a bit. I haven't tried it yet since it's blocked in at the back of my garage.

 

If it'll lift with your foot, put a spring on it to lift it, master cylinders don't push back enough and aren't meant to.