Unfortunately, no it did not solve the problem. Maybe slightly better, but still feels like there is air in the system. Truck stops fine, it will slide the tires if you push it down hard at speed, but the pedal goes to the floor if you push it there at a stoplight.
I have stainless flex lines on the way and I have a nicer crossover tube than the one under my truck that I got at the pick a part. When the flex lines come in, I will replace all of that and see if things improve.
It did seem to get a little better on a 40 mile round trip this afternoon....

 

Stainless flex lines did not fix the issue. They did make the pedal stiffer however, which is a step in the right direction.
I tested the master cylinder with plugs.
First with the pedal at the top, will not budge with the plugs installed.
Then tested it by stroking to 1/2 pedal movement and then having the plugs tightened, just thinking there might be some problem / port / scratch in the master cylinder allowing fluid to transfer between the two pistons within it. Nope, master cylinder is firm as soon as the plugs are tightened.

Testing will continue...

Anyone ever had this issue?

Thanks!

 

Mine was bad lines. Mostly the rubber lines, bad blocks, and a bad proportioning valve.

 

I had suspected the rubber lines and crossover line under the engine and replaced them. But the pedal will still slowly sink to the floor. I bled the rwal solenoid and proportioning valve, but the problem still persists. Very strange issue I have here...

 

I would say what all did you replace?

 

Think I might be tempted to find a safe area, that you can give your antilock system some serious exercise.

 

Master Cylinder (4 times)
Front Calipers
Front Pads
Used Proportioning valve and antilock solonoid block from another vehicle.
Rear Wheel Cylinders
All rubber lines with Stainless Flex Lines
Crossover line under the engine.

 

Just tested the antilock solenoid block by inserting a cut off q-tip into the hole normally covered with the rubber boot. Cranked the truck so the power brake booster would work and had my helper apply the brakes repeatedly, with the pedal slowly sinking to the floor each time. Accumulator piston within the antilock solenoid did not move. I had the q-tip fully inserted until it bottomed out to feel for movement. So I think this clears the anitlock accumulator from being the issue.

The proportioning valve spindle did move each time, protruding as the brakes were pressed, but it does that on my other vehicle, a 3/4 ton chevy and no issues with the brakes on it.

 

I like that idea. Next time it rains I will head down to the large parking lot near here. Otherwise I can go find a dirt road...

 

Dirt road would be good. Easier on the tires.