I have a major brake problem. I have replaced: rear wheel cylinders (new). front calipers (new), master cylinder (new), vacuum booster (new), all pads and shoes and three brake lines and still have no brakes. I have reset the proportioning valve and suspect it may be damaged. When I block off (isolate) the master, good pressure. When I attach the rear brake line I get half pedal. When I attach front line -no pedal at all. both front lines have been repaced. I find no leaks anywhere, even after cleaning with carb cleaner. Anyone have any ideas?

 

This thread is kind of old, and you would've probably got better answers by starting your own thread than reviving one from the dead.

Nonetheless, I'll see if I can offer up some things to check.

First, make sure your rear brake drums are adjusted correctly.

Are all of your brake line fittings tight? Did you do a double flare on the brake lines to ensure a solid seal? Teflon tape on the threads ensure no leaks whatsoever. How are the soft rubber lines? Are they in good shape?

Are you bleeding the lines in the correct order? If you don't, residual air pockets can be trapped in the brake lines. Bleed the Right rear, left rear, right front, and then the left front.

Have you tried removing the proportioning valve from the equation? If you haven't, give it a shot and see what you get. Plumb the front brake lines to the big reservoir and the rear brake lines to the small reservoir.

Until you get a new proportioning valve, you can run without one for a while. To make the light go off, all you have to do is jumper the wire going to the proportioning valve.

You could always pull the proportioning valve out and pull it apart and see if you can clean it. Just make sure you know how things came apart and went together.

 

The front rubber lines are new. I have had the valve off to reposition the shuttle as the pin was out, indicating front brake low pressure. The light is out. One of the guys a the local NAPA is very knowledgeable and suggested I replace the valve. As I said, I have cleaned and checked all connections and find no leaks, but I have a section of line that runs along the frame from the valve to the rear junction/splitter that I cannot quite see, just no sign of wetness. I need to get the brakes right to have the truck inspected for title as I have change the sheet metal, cab included, because original was totally eaten up ----no floorboards. I am going to change the bed --again-- because I have an offer of a much nicer bed. I will definitely check the frame lines at that time. I have also located an aftermarket valve, all bass, OEM specs for $65.00+ shipping. Thanks much for your reply.

 

You did bench bleed the master cylinder before, right? If so, then I'd just crack the back right tire's bleeder screw and try letting it gravity bleed for about 30 minutes or so. Just remove the cap off the master cylinder, loosen the bleeder screw, and the brake fluid should flow from the high point (master) to the low point (bleeder screw) by force of gravity.

If this doesn't work, you might end up having to try a vacuum brake bleeder to get fluid to the front and rear tires. If the lines were dry, it's going to take a decent amount of brake fluid to fill them back up.

If you don't want to try a vacuum pump to bleed the brakes, you could always get a one man brake bleeder kit from the auto parts store. It's around $5 if memory serves, and I used one to bleed the back tires on my truck. Works great, just follow the instructions. All you do is hook it up to the bleeder screw and pump the air out of the lines with slow smooth strokes until it's filled up, empty it, and repeat until the air is out. You'll have to hop out and check it to be sure the air is out, and stay on top of the brake fluid level.

For $65, it wouldn't hurt to replace the brake pressure differential valve if you think it's defective. And, the way it's sounding, it sounds like it is.

 

Is the bleeder at the top of the calipers? Some vehicles it is possible to install them on the wrong side, with the bleeder at the bottom.

 

I'm back. I have 1 question. After replacing the proportioning valve with a new unit, I have a pedal. The question is: Is the shuttle valve inside the valve block supposed to move when the brakes are actuated. Mine does, but not much and it moves right back when the brakes are released. I have spoken to mechanics and NAPA store personnel only to get conflicting info. I have been told that it moves because this allows the pressure to equalize and I have been told that it should not move at all. Can someone please help. If I am in the wrong place, will someone guide me to the correct page ?