losing brakes

Do the trick to get the pedal to fall,but do not stop. Then, while still backing and turning, pump the brakes to see if the pedal gets hard.
If the pedal gets hard; then this is a mechanical issue. Something has knocked the piston back, or the pad is not anchored properly or the pads are stuck in a rut in the caliper ways; Ima thinking this last one. Now,this turning and backing thing, has released the caliper, the pad jumps out of the rut, moves into a proper braking position, and you feel it as a drop in the pedal, which you interpret as a pressure loss. Pumping the pedal pushes more fluid out to the caliper and restores the braking action, and pedal-hardness.
But if the pedal does not get hard, then IDK, but here are a couple of other checks;
Check your front brake hose routing, just because, not that I think there is an issue. Next check your lower control arm bushings are not floppy.
If this is OK then next check your front wheel bearing adjustment; With the wheels off the ground, and the steering wheel sorta centered; give the lowest part of the tire a solid kick, and a hard tug.Hit her hard, you can't hurt it, you'll break a toe first..

Finally;Check your power booster operation
turn the engine off, and pump the brake pedal about 5 times, to empty the storage chamber. Then,in Park, press down and hold the pedal while starting the engine. As the engine idles, the pedal should fall about 1 to 1.5 inches, within just a few seconds..
Do this at full-lock left, and at full-lock right; It should drop the same.Steering wheel position should make zero difference. This is just to rule out a booster issue.
That's all I got.

If the caliper ways are rutted, you will have to fill them and dress them down to fit. I use a hard brass brazing rod. Make sure the caliper pins are not bent and move freely in their sockets.