Brakes driving me crazy

[1500ram12]

So on my 1990 w250 12v Cummins I've been struggling with getting the brakes figured out.

Everything is brand new. basically did a fluid flush yesterday to ensure that there's no air in the system. ABS has been removed completely (not that there's much on these trucks).

When the truck is OFF the pedal is perfect.

When the truck is running the pedal will sink to the floor with normal pressure. Bled the brakes with it running and nothings changed.

Pinched off the rear rubber hose and the pedal was firm but did slowly drop a little. Thinking that the hose wasn't completely closed off.

Did the same for the front and the pedal didn't drop.

There is zero leaks in the system.

I'm at a loss on what's going on

 

[fireflymedic]

Diesels don't get vacuum from the engine. Not sure where a ram gets it but on a Ford ambulance I was assigned to it was a pump ran off v belt. It also ran the power steering so if belt broke you lost power steering and brakes.

 

[1500ram12]

It's similar to the Ford but not belt driven it's gear driven. Small gear on the lower right driver's the vacuum pump and power steering. From everything I've read it's not vacuum related, at least not completely. It's still possible that this master cylinder is bad also. I have another test to try tomorrow that should verify if the master cylinder is good or bad

 

[bm02tj]

When you are done replace the hose you pinched as you ruined it