Brakes were squealing pretty bad

Yes, that was the procedure I used for the first round of bleeding right after caliper replacement with a helper in the cab. Pedal depressed - bleeder open - pedal held down - bleeder closed - pedal up - repeat. I had removed the old calipers and during replacement the reservoir was ran dry. I installed new calipers and brakes topped off reservoir and began brake bleeding with helper.

The ABS bleeding and other subsequent bleeding were done alone with brake bleed bottle. As follows:

Bleeder bottle hose connected to bleeder and 1/3 full of fluid - bleeder opened - enter truck and depress peddle until no visible air bubbles - exit truck - bleeder closed - repeat in order of distance to master cylinder.

Since this post I have continued troubleshooting and this is what I have found. 1 caliper was not replaced (driver rear) it had no damage was in good condition. While bleeding I noticed it didn’t matter how open the bleeder was (1/4 turn, 1/2, etc) it would leak fluid from around the threads. I found a replacement bleeder screw and solved that issue.

I have bled the entire system several times using bleeder bottle method with no change in brake pedal. Also went through ABS bleed procedure again with no change.

Decided to change up bleed method. Using a long pipe wedged against the seat to depress brake pedal. I went through ABS bleeding procedure with pedal depressed throughout. After this I used this method to rebleed all 4 wheels. At this point very little air was coming out of the lines. By the third wheel I had almost no air escaping.

My procedure with the pipe wedge was as followed:

Pump pedal 2-3x with pipe - wedge pipe between seat and pedal in the depressed position - connected bleeder bottle to wheel - open bleeder - wait 4-5 seconds - close bleeder - pump pedal 2-3x - reset pipe - back to same wheel - open bleeder - repeat until no air bubbles. At the end there was no change.

I cleaned every brake surface I could find and inspected everything with a flashlight for leaks. Topped off the master cylinder turned the vehicle on and drove around the neighborhood. Brakes are the same. Pedal travels to the floor and my stopping power is at the end of travel. Parked the vehicle. And inspected every hose, caliper, the MC, booster. Found no sign of a leak. Reservoir was at the same level.

During my research I found a post stating if the ABS pump is bad it could cause this symptom. I pulled the fuse to this module with no change. My scanner has options to activate the valves on this pump. With the pedal depressed I energized each valve independently I believe there were 6. Some of the valves you could hear an audible click and some you could feel the pedal give way slightly. In the end this did not effect brake performance. There are no ABS codes stored.

With the vehicle engine off I can pump the brakes and the pedal gets hards. With foot on the pedal and vehicle turned on. The pedal will immediately and smoothly go to the floor with no resistance. With the vehicle "on" the brakes can be pumped and will slightly firm up and will slowly sink. If pressure is removed from pedal for a few seconds that firmness is gone and pedal is back to the floor.

Master cylinder was a new unit from NAPA. Of course that doesn’t mean it is a working unit. I did remove the lock ring from the old master cylinder and disassembled looking for seal damage etc. The old unit appeared to be functioning and had no signs of internal damage or heavy wear.

The ABS pump/module seems suspect to me. Is it possible when the reservoir went dry this unit could have been damaged? This is a used truck I purchased 4 years ago. It had 112,000 miles. It currently has 160,000. I had never changed the fluid during my ownership. The fluid was very dark.

Video attached. Pedal held firm from what I can tell. Not sure how much play there should be. You can see the travel distance when vehicle is started.

With the vehicle on pedal reaches floor. Vehicle off, pedal pumped, and held there is very little movement. No sinking. What I meant was, you stated to pump and hold pedal, I am not sure how much “play” (movement) is consistent with a bad master cylinder. I am going to isolate the master cylinder and plug both primary and secondary ports and check for change in performance, if any.

Was able to locate appropriate brass plug fittings. Plugged both ports on the MC peddle inside the cab was firm. Vehicle turned on with master cylinder plugged peddle was still firm. Removed near side plug and replaced brake line. Far side plug still in place peddle was soft. Replaced near side plug and re installed far side brake line pedal soft.

Master cylinder appears to be functioning. However, I did find a very small amount of fluid building up around the gasket where the reservoir seats against the master cylinder body. With the master cylinder clogged on both ports this fluid becomes more obvious but does not quite leak out. Due to this I have decided to return and replace the unit. I will update my results after replacement.

New master installed with no improvement. Was able to secure a salvaged ABS pump/HCU swapped the control module from my vehicle onto the salvaged unit unfortunately this also did not change pedal performance. All bleeding procedure were performed with new master cylinder and ABS.

I decided to start from the beginning. Removed all 4 wheels inspected brake lines and and calipers again. I clamped off all 4 rubber brake lines at the calipers. With vehicle "on" pedal was firm. Removed rear right clamp, pedal firm. Removed rear left clamp, pedal firm. Removed front right clamp, pedal soft. Replaced front right clamp- removed front left clamp, pedal soft.

Removed front left caliper with brake line attached and unclamped, I depressed pedal. The top caliper piston extends fully the bottom piston extends only 1/8” to 1/4”. Using a caliper piston clamp tool I retracted the top piston and left the tool in place, blocking this piston from extending. With the truck on I depressed the pedal and the bottom piston extends fully. Once again I removed the piston clamp tool retracted both pistons flush with the caliper. With the vehicle on depressed the peddle and top piston extends fully bottom does not. I retracted the top piston, blocked it from extending, and depressed brake pedal allowing bottom piston to extend. With rubber brake line clamped. I connected the bleeder bottle and opened the bleeder. I depressed the brake pedal (edit: I did not depress pedal here, I retracted the piston) attempting to isolate any trapped air on that side of the caliper. Several bubbles exited the caliper. This however did not change caliper piston extending when both sides are unblocked

I performed the same test on the front right caliper. And the same issue is present except the bottom caliper extends fully and top caliper only very slightly.

Both of these calipers are new out of the box. Pistons extended fully when one side is blocked but only one piston will extend when both sides are open. There is only one hydraulic brake line going to the calipers.

Could this be an air pocket trapped somehow?

Bad brake line?

Both calipers bad out of the box?

How can I isolate the problem further without swapping a bunch of parts?

Any advice is welcome thank you for your time and help up to this point.