spongy brake pedal

if i hit the pedal hard brakes lock on.

but a slow press some times the pedal just slowly sinks down. and i lose the bite unless i hit the pedal again.

the cars has goodridge stainless braided brake hoses 6 piece kit

Front brakes:
AP Racing 4-Pot Calipers with 330mm grooved AP discs

Rear brakes:
305mm vented disk conversion

Ferrodo Ds2500 pads all round

no apparent loss of brake fluid anywhere

ideas