Have no pedal when truck is running. Replaced booster pump twice and master cylinder all made no change. Bled brakes after all replacements.

 

pedal will drop when running and vacuum is applied from engine. normal operation. Did you bench bleed master before the install?
How is adjustment on rear drum brakes? what year Durango are we messing with? Should ask that 1st, as "adjustment" only applies to drum brakes although I have seen calipers not give a firm pedal if, say the pads aren't engaged in the machined "ways" that are meant to hold the ends of the pads. and the metal pad backing will flex.
speaking of flex, how bout the rubber hoses? Ive seen them with blisters in them that expand, when brakes are applied/ and they take on the pressure of the brakes being applied. so

 

Sorry 2003 all calipers and rubber lines seem good didnt bench bleed master but I'm getting fluid at all 4 tires. Bled master after install. Just seems funny all i do nothing changes. Even tried to bypass abs changed nothing. This is a 4x4 with the 4.7. On the first booster i replaced with truck running removed vacum lines and had pedal. Replaced both front brake lines and 2 booster pumps because i was told first one was bad.

 

If you bleed with the truck running, do you still get fluid?

 

Havent tried that

 

So do you have REAR DRUM brakes??
If so, did you adjust them properly?

 

03 are disk in the rear.