Bad brake caliper in my 72?

[HHStang]

I'm not sure what is wrong, but my pedal is soft. I've bleed a few times, new fluid, etc. and still soft. When I put it on the road, I used a residual valve recommended by MP Brakes for the front discs. A couple miles down the road, the passenger caliper locked. When I loosened the bleeder, the caliper released.

I replumbed without the residual valve using the front two ports of the factory (drum) dist block. The pedal will not get solid as it was before (it goes to the floor basically).

I clamped each soft line going into the calipers and when I did the ft passenger, I got the solid pedal. I'd assume the caliper is bad, but I see no leaks and the piston will go out and in.

Is it the caliper? Distribution block? Thoughts?

Thanks!

 

[2nd Mustang]

I'm going through a similar problem on my 67 coupe with Kelsey Hayes front calipers. My right front rear piston was dragging really bad causing the pads to wear out unevenly. I replaced the pads and calipers (both sides) then it started locking up. I replaced the master cylinder and it still locks up. My next thing to do is to replace the distribution block. There's nothing left in the front braking system. Good luck with your situation.