If you've done a bunch of work on your brake system and you've bled the wheels several times and you still can't get a good brake pedal out of it, try this. Take the vehicle into a vacant parking lot and accelerate fast enough to lock up the wheels when you apply the brakes. Lock the brakes up several times and recheck your brake pedal. You might find that your brake pedal feels great after doing this. Just be sure that you've exhausted all other possibilities before doing this. It does work though. Here's a video.