Brake Issue?
 

About a couple months ago, I experienced what I would consider a brake failure. It felt like things were dragging after a bit while backing up and then after driving a bit, the pedal basically goes straight to the floor providing no gradual set of braking, ; the brakes are basically on or off at that point, however when the engine is off, one can pump the brakes hard. I replaced both the booster and the master in the front and while things are slightly better, the same condition basically re-appears.

Are you losing brake fluid? Either way, think I would pull the drums, and see what's what...... if you are losing fluid as well, might be wheel cylinders, or, it might be a popped line.

I dont see anything on the rear wheels or dripping out of the drums, and no puddles, which is what also adds confusion. I can pump the brakes with the engine off and everything gets firm. Things are ok for maybe the first few minutes of driving, except what feels like dragging when backing up at least. I replaced the passenger rear cylinder about 3 years ago because it was leaking and making a mess. Also my 01 QC has the 03 Durango dual piston front brakes if that makes any difference, but that has been on the truck for over 2 years now without any issues.

The line running to the rear can pop, but, fluid doesn't hit the ground immediately.... it pools in the frame, or someplace, and drips down when it gets full. Of course, driving displaces the fluid..... so it doesn't drip when you are stopped..... only when you are moving right along.

I have seen that brake pedal behavior before though.... and it was due to a fitting I had forgot to tighten.... (a leak would do pretty much the same thing.)

Have you checked your proportioning valve? I've seen those cause some odd problems at times.

how does one test the prop valve?

What year truck , what's your location ?
I'm glad I did the whole brake system about 12 years ago...(it's first 7 years in Illinois salted roads)
yes, little seeps along the lines and the junction box at the rear axel , sending the fluid to the brake cyl. are all known maintenance .
I try to give a qiuck spray of PB blaster or such on the bleader valves hopefully once a year. , and been through a few pair of pads.
I think with the new brake fluid, brake pad , shoe material for me in the rear ) calipers, and rotors, my truck probably brakes better than new.
just saying...

The truck is an 01 QC with 03 Durango front hoses, spindles, rotors, and calipers. Location is SC. Going to try and replace the rear brake rubber line first (since I have one for the eventual upgrade of the rear from drum to disc) Still trying to figure out the best way to test the prop valve though.

check it all
 

I suggest pulling the rear drums checking it all out.

Funny but I had no rear brakes for how long I dont know till I decided to look them over I found both cylinders locked up useless. Im 100% sure I moved to Arizona like that. What angers me is within the first month of the move I had a shop check my breaks out and replace the DOT 3 do a flush they charged me and said everything is good. This was maybe a year before I found my rear cylinders were locked up. I tried to bleed the rear cylinders and a small amount of black goo came out and stopped after replacing the cylinders I bleed them and a ton of black DOT 3 came out that was crazy.

You just need to crawl under and check the system 100%

My 03 has discs/!drums combo in the rear. The drums are for the parking brake. Well, the liners fell of the shoes and caused all sports of issues. Didn't figure it out till I pulled them off.