I have the usual 280zx front strut and disc brake setup on my 72 wagon. My issue is when I first drive off the brake pedal operation is soft. After about 20 minutes of normal driving the brakes start locking up and the brake pedal gets really hard. I rebuilt the front calipers (sand/polished piston and bore) new seals and bled Master. I thought at first it was just the front brakes but when I checked the rears (drums) they too were locking up. If I let the car cool down, the brake pedal is soft again until I start driving it for awhile then they lock up. I am running the 280zx dual Master and just picked up a porportioning valve from a 81 280zx. The problem with this setup is my original setup has 5 lines going into it plus brake switch and the 81 280zx only has 4 and no brake light switch.
I was told that the wagon does not have a porportioning valve rather a hydraulic pressure switch in the brake system.
Can anybody give me some suggestions on this problem?