Rear brake pressure regulator valve, Brake repair Options

[DamonsCarrera]

The brake pedal on my 914-6 is very spongy, even after repeated bleeding with a pressure bleeder. I isolated the problem to the brake-proportioning valve or pressure regulator. I cannot seem to get the brakes properly bled with this valve in the system.

I've read other posts by some here and it seems this valve is a source of some debate . Is there some trick to bleeding the brakes with it? Do I need to bleed the brakes the old-fashioned way, have someone push on the brake pedal?

[toolguy]

No trick concerning the proportioning valve. . . all that is inside of it is a sliding piston and a big spring. . . the piston moves and cuts off brake fluid to the rear calipers when a preset pressure is exerted. .
When I redid my entire brake system, I couldn't successfully bleed it with a pressure or vacuum single person system even after a dozen tries. . . . finally had a friend come over and and we did it the old way still took going all the way around 4 times to get a rock solid pedal. .
What I finally figured out was when cracking the bleeders loose to bleed, air was seeping back into the calipers from the bleeder threads. .