98 f150 soft brake pedal?

[Eric]

i have a 98 f150 195000 miles. the pedal seems to go way to far down. all other vehilces ive drove had a tight pedal. mine only gets tight if i pump them while stoping. ive bleed the brakes and took it to a shop and had them bleed them. no difference in brakes. what could be the problem. there are no leaks in the lines. could it be the rear drum brakes, master cylinder, brake booser? i have no idea i just know it isnt right does anyone have an answer? dont want to spend a bunch of money and replacing things that are not the problem.