1) I don't understand how the LPSV is supposed to function. Basically the housing is a metal body with a straight vertical borehole. When the bed comes down under load the bar will push the plunger up in the housing. I imagine this would close up the brake line to the rear drums. More load in the bed means more braking power to the rear wheels. Does the plunger open up a bypass inside the housing by which added pressure is going to the rear cilinders? Does anyone know how it actually works, the LPSV?

After taking the valve apart I found lean fuid inside. The plunger/needle/piston is freely moving up and down 2 millimeters or so (0,08").
Then I bleeded all 4 wheels. Also I tried to bleed the LPSV. But no fluid is coming out of bleeding valve at the back. The bleeding valve at the back isn't there for no reason. No bleeding fluid doesn't look good I guess. On the other hand the brake line exit to the rear cilinders sits higher up in the housing. No air will be trapped inside the LPSV housing then. What's the use of that bleeding valve?

2) Rear drums do get fluid since I bleeded the back. And the brake shoes do come apart (with drum taken off). With the rear axel put on stands I run first gear. I firmly push down the brake pedal but I cannot stop the engine. Wheel do slow down somewhat. Same thing in 2nd and in 3rd gear: I can't stop the engine, wheels keep on turning. Doesn't feel right either.

Thanks for any input.

 

Well, according to "THE Book", the LPSV should bleed exactly the same way as any of the wheel brakes do. Open the bleed valve, press the brake pedal slowly down, close the bleed valve, release the brake pedal, open the valve, press the pedal, etc, until the fluid runs clean, and no air bubbles come out.
If no fluid is coming out, perhaps the bleed valve has a clog of some sort. Doesn't take much. stick a small piece of wire into it while it's open, to make sure it's clear.

If the wheels can't be stopped by pressing the pedal while they're turning, it sounds like maybe they're not aligned correctly. They have an adjuster screw. Have you tried adjusting them? The Book shows how. Essentially, rotate the wheels backwards, like you were backing the truck up, the press the brake pedal. Keep doing that until it no longer "clicks". When adjusting them, make sure you have the correct load on the rear axle. It should be 1, 984 LBS. Same for when adjusting the LPSV. It could be the LPSV isn't properly adjusted as to why the brakes don't stop the tires, although I suspect the adjustment of the brakes to be the problem there.

Remember, THE BOOK is your best friend for all this
Good luck!
Pat☺