lots of good information on the pedal pumping procedure, but only one or 2 mentions of the shoes themselves.

the reason it's important to check the shoes for proper adjustment, is because unlike a disc where the pad "floats" right at the disc with no return spring, a drum brake has springs to physically pull the shoes away from the drums.

if you do not have the shoes adjusted properly, so that they are ever so slightly dragging on the drums, then your return springs are pulling them to far back in and the wheel cylinders are being "fully compressed"

when you pump the pedal, what you THINK is a soft pedal from air in the system could actually just be the airgap between the shoes and the drum being taken up by pedal stroke.

add in the fact that all 4 of your wheels are drums, and it's even that much more critical that your shoes are properly adjusted and seated.

--jack on one wheel at a time, have a helper step on the pedal to push out on the shoes, then grab the wheel and try turning it back and forth. this will help to seat the shoe. then release the pedal and click out on the adjuster.

this may need to be done a few times if the shoes are new, as the high spots will wear away quickly, and the brakes will go out of adjustment very fast until the shoes fully bed themselves to the drums.