1978 k35 proportioning valve question

[Jwedd]

I'm dealing with dragging front brakes, both equal in drag. Rears not heating up. The last trip of 10 miles, I had to pull over to the side and let the rotors cool off. After a few pumps of the peddle, something released, and I was able to get home ok. I'm not sure if the brakes have ever been bled, so my goal is to replace calipers, hoses, lines, and master, thinking that one or more of these could be the issue. The master and steel lines from the master to the prop valve are quite rusted on the outside. I suspect the issue is in the common line before the prop valve, or the master itself. It could be at the prop valve too, something cruddy plugging up the front side that keeps it from releasing.

I'm not sure what to do with the prop valve. It looks very different from the aftermarket PV2 units that are out there, and also different from a used ebay unit photo. This one looks considerably more beefy. JB8 brake system with hydroboost. Should I leave it alone?

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[Goldie Driver]

I would leave it alone. The OE are better built and my experiment with an aftermarket PV2 unit, I believe, gave no better results and after about 3 years leaked. I had to put OE back on late last year. The rubber lines from the frame to the caliper can go had and cause calipers to hang. There are some tricks to determine where the issue is that you can try but I can't remember all of them. One is to loosen the bleeder screws when the calipers lock and if the calipers free up it is residual back pressure not calipers. Another is to loosen the 2 bolts that hold the master cylinder to the booster on a non hydroboost and if the brakes release the portion lower than that is probably OK. I am sure others will chime in with additional details.

Good Luck !