one thing ive found handy is those little hose clamps. get some of them, then block off a flexi hose one at a time, then press the brake pedal. if theres air at the nominated position, then the pedal will get MUCH better. if nothing helps, then block off all hoses, and press again. if the pedal doesnt get better, your problem is in the master cyl/lines.

can you get any wheels to lock up on a hard stop?

also, does the.. umm forget its name.. the safety switch incase you get a major pressure differential from front to rear... is that thing manually resettable on dattos?