1992 Brake issues

[Yellow92]

I know there are a thousand brake posts, but I have not seen one with this symptom.
Just bought this 92, with 26K on it. Drove it home, was 2 hours away, and on the way
home pedal seemed to sink further and further towards floor. Had to press very hard to get
brakes to work. Long story short, turned rotors, new pads, checked ABS unit for air as FSM states.
Flow out of rear calipers seemed slow, also pedal would not go to floor when bleeding.
Front calipers bled normally, all clear fluid out of all calipers.
Hear swooshing sound when pushing down pedal, but I hear no leaking when depressed.
As it stands now, car stops straight, but it seems I need to press to hard on the pedal to make it stop.
Also, is it normal to have a hissing sound at the back of the engine when car is shutoff, doesn't seem to
happen all the time, but have heard it a couple times. The pedal does not always go down when car is turned on, indicating
intermittent booster issue. Thanks for reading my loooonnngg description. :ugh

 

[Hot Rod Roy]

Those are all signs of a defective brake booster.

 

[Yellow92]

Thanks, I think someone may have did a rig-job on the hose going from the bottom of
Master Cylinder to the ABS pump, not sure if that may be an issue also.

 

[Hib Halverson]

My guess is you have a problem with the brake booster or the hose which runs between it and the intake manifold. Either there is a leaks somewhere in the system or the booster if failing.

As for the ABS prime pipe...I'm not sure what a "rig job" means, but the instructions for bleeding and or servicing that are in the Service Manual.