Help - New parts and soft brakes

So of the myriad of issues im currently chasing on my 01 5vzfe 4wd, my brakes have been giving me a headache.

I had NAPA reman 13WL front, oe drum rear, with stainless lines and stock booster and master. Pedal was firm but with the engine running the pedal went slowly to the floor and I figured had a leaking master. Engine also pulled to one side while braking, so I needed to address that.

So I replaced the master with a FVP rockauto master cylinder and confirmed the caliper was seized so replaced it with new powerstop 13wl calipers. New pads in the front and rear.

Booster is original, wheel cylinders are original.

Bench bled the master, bled all the lines multiple times, no leaks, no abs, and I have a firm pedal with the truck off. As soon as I turn it on, pedal goes to the floor. Multiple pumps builds pressure but goes to the floor still. Truck stops and the brakes work, but im thinking I got a bad master. It just has almost zero feel in the pedal.

Any other ideas?

 

Below is a Cut and Paste from “Car Talk” online search below:

Does this truck have vacuum assisted brakes or hydraulic assisted brakes? If they are hydraulic - run off the power steering pump - the booster may have failed.

If the booster is vacuum assisted, it sound like it has failed although I’ve not had a vacuum booster fail that way.

 

^^Yup.
He beat me to it.

 

Not sure if entirely understand the why. Looks like this is the link you found.

If the booster fails shouldnt the pedal just become non assisted and firm? They dont really explain it or how to test. Ill keep digging on my end, but if people have ideas im open.

As of right now i know I missed the bpv so I need to assess that. But drums are adjusted correctly and calipers are oriented correctly with a new, bench bled master and literally about 3 quarts of fluid run through the bleeders.

 

Im looking at the used / junkyard booster options, toyota shows that the 3rd gen 4run has a different p/n than the 1st gen tacoma.

Are these interchangeable?