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It sounds as if there is not enough pressure in the system. This could be the result of a faulty master cylinder, or inadequate brake fluid. It is also possible the piston assembly in the calipers have a fault.
it sounds like to me that your master cylinder might be bad
It sounds like there is a problem with the proportioning valve. I highly advise you to seek professional help with this repair. This is a very dangerous situation and needs to be corrected ASAP.
air still in lines. rebleed
ABS brakes are not spongy. If you have spongy brakes the reason is that there is air in the system. You need to have your brakes bled.
It would be helpful to know: What vehicle you are working on. The condition of the rear brakes, and were they also bled. Does the brake fluid level stay full, if no then there may be a brake fluid leak.
You need to bleed the brakes.
SOUNDS LIKE (NOT ENOUGH VACUUM) CHECK FOR BROKEN OR MISPLACED HOSE)S This buzzing noise maybe something with the ABS system. I don't know if any of the lights are on, on the gauge. If the brakes were just changed maybe they need to be bled better. Low fluid in the master cylinder, try rapidly pumping the brakes, if that helps then it is a fluid issue or air in the system and needs to be bled.
Master cylinder
Did you replace the master. It might be by passing.
You either got the wrong master cylinder or you haven't actually bled all the air out of the system.
You have air in the lines and they need to be bled out.