Random out of the box thought I don't know if this is possible

But your rubber hoses going to the axle and calipers good? With brake booster off its not supplying lots of line pressure- but when it is maybe a hose is expanding?

I didn't see if you replaced these

 

I used a Russel braided stainless kit and replaced them too while I was doing everything. I pretty much replaced all the parts so I wouldn't ever have to do this again lol

 

Switch to hydroboost system if you need to switch out brake booster - junk yards around michigan 55$

 

I would say it's the master cylinder. Also try pressure bleeding Vs. vacuum bleeding.

I typically get much better results when doing it this way.

When you crack the screws vacuum bleeding you can actually introduce air into the system. It gets in through the threads. I find I typically have to go in and do it old school with someone's help after that to get a good feel. At least until I bought a pressure bleeder. It force's the fluid from the master through the lines as you crack them loose.

 

Hopefully it is lol

And my vacuum bleeder shouldn't be letting air in through the threads. Before I installed all the calipers, I toke the bleeders out and I applied a small bit of teflon around the threads and made sure it wasn't hanging past or get into the caliper and clog the bleeder. Can also verify this isn't happening because I get fluid out of every one very easy

 

yep. this was my problem. i had my girlfriend help me old school style and built up good pressure at the pedal with a good bleeding

 

Replaced the master cylinder today.

Big improvement in it. Kinda. The pedal travel is consistent now with the truck on or off.

Still have a lot of air in the ABS, worked a good deal of it out the rear. No air coming from the rear now.

Small amounts of air still coming from the front. Fronts still don't seem to be engaging at all though.

One thing I noted with the old master, it was super easy to push the valve in and when I did, the front port would get a big stream of brake fluid while the rear port would kinda trickle and barely shot out. The new master cylinder was a bitch to get the valve to move. I ended up sticking it in the truck and bench bleeding it with someone working the brake pedal so I could watch.

 

Ended up finding out the ABS pump doesn't work. Bled and bled and bled, had my old man helping me and we could not get the pump to cycle any air out.

After a bit a buddy of mine came over and helped a little too and he called his friend who works at the dealership, an hour or two later and this guy messing with the tech 2 tool and trying to get it and nothing. The pump seems to be air locked or something. The fronts just won't grab and we can't get the air out of the pump. The rear works beautifully.

We also checked all the brake line routings to be sure and all was where it should be.

I have everything I need to delete the ABS, tomorrow I'm deleting the ABS out and will finally have working brakes again lol

I'm hoping after this, I'll never have another brake issue again with this truck

 

When I replaced my brake lines, I filled the system by pumping fluid through the bleeders in the order of first r rear, then l rear, the r frnt then l front. I had to keep removing the extra from the master cylinder. It needed no bleeding afterward. Sorry I didn't post this sooner in case it might have helped.

 

No worries. I never worried about doing that except the master cylinder lines before the ABS.

Pump never worked on the front side. Don't know why.

I deleted the ABS and rebled it all and the pedal is rock hard and the brakes worked damn good for the stock style calipers, and rotors. I could probably launch myself through the windshield if I slammed them hard enough.