My 2005 Ram 3500 dually has been issues with the brakes dragging and the pedal going soft while the truck is running...since it was all four calipers dragging I started out replacing the master cylinder, which didn't help anything. Then I swapped calipers with my brothers dually(its an 04). Still no improvement. Then I switched the hyrobooster and ABS modular/diverter. I still has not isolated the problem. I know dodge is known for poor brake hoses and I haven't tried replacing any yet, but what would cause my brake pedal to feel good and firm when the truck is shut off but once I start it, it fades away? It still has good braking power, its just that the calipers don't release all the way...I can take a pry bar and pry the pads back and the hub with spin freely. Any advice?? I running out of things to replace.

 

i had an old chevy 2500 (2000 model old style) that did that on one front hub.

they replaced the brake assemby on that wheel and all was good.

also had an older chevy, 77 model and the front wheel brakes would hang or drag as you say.

It was the brake hoses from truck frame to brake assembly, the hose had come apart inside and would block the fluid from returning to the master cylinder.

when one of your brakes appears locked, loosen the brake line from the brake, see if brake loosen up. If so then its your brake lines blocking the return of the fluid. Hard to believe it can block the fluid but it did on the old chevys. No exterior leaks, etc: just interior line breakdown and blockage.

gm had a big problem with that years ago on their old chevy trucks. many old boys bought a complete brake job until some good old redneck mechs. finally figured out what was what on the bad rubber brake lines.