Technical Brake Problems on a 1941 Ford Tudor

I have a 41 Ford Tudor and I just put disc on the front. The discs work fine with the single master cylinder, I have good pedal pressure and the car brakes really good.
The problem I have is that when the car is on a slight uphill incline, I lose pedal pressure. The pedal goes all the way to the floor and I have to pump it a few times before it even builds pressure, and usually not till it levels out. And it doesn't happen all the time. While driving going uphill it is fine.
So I installed a 2 lb residual valve on the front line and 10 lb on the rear line as well as a proportioning valve.
Pedal pressure is the same as before, but I am getting the same problem with losing pressure on a slight incline. I have bled the brakes at all 4 corners. I replaced the master cylinder about a year ago, but I didn't have this problem with the drums. I do have the residual valves in the right flow direction.
So I am a little stumped as to what to do. I am worried that I will change to a dual master cylinder and still have the same problem. Is there something I am missing here? Should I install a 10 lb valve on the front instead? Or will that keep the calipers locked up?

 

You really need changing to a dual master cylinder.
There already is a residual (check) valve in the stock '41 master, unless you removed it, which should be removed because of the disc brakes. You want no more than a 2 lb residual to the front discs, and 10 lb to the rear drums.
It sounds like something in/on your front suspension could be contacting the calipers, causing them to retract more than necessary, if they are floating calipers.

 

Thanks V8 Bob. I guess I will try changing to a dual master cylinder. Someone on a different thread mentioned the AMC master cylinder being good. Which adapter do I need. I have seen two different styles. One is just a flat plate and the other puts the M/C about 3" away from the original mount.

 

I use adapters made and sold by Ch***is Engineering Inc, that allow most Ford 2-bolt masters (Mustangs in my case) to bolt up to the '39-'48 3-bolt bracket. These are flat, while the thicker 3" or so adapters may have an angle that helps clear the dual master from the floor.