Crazy and persistent brake issue
 

I'm fed up with this problem and throw myself on the mercy of the forum.

Not sure when its started but my brakes have become way too soft. They work ok, enough to engage the ABS. BUT you can press the pedal to the floor without real difficulty. Very creepy. To try and fix this I have:
Bled the system numerous times
Rebuilt front calipers with all new seals
Adjusted pedal height and rod
Bled the system numerous times
Replaced the master cylinder
Bled the system numerous times

I've got SS lines all around. Everything else brake related is stock.

Brakes are not my forte, but you may have a leak in your brake booster system. Check the rubber hoses located along the fire wall. One loops into the UIM at the passenger side to get vacuum and another loops into the brake booster (the big drum behind the master cylindar) on the driver's side.

If the vacuum booster leaks, the brake pedal will get hard and you'll have to push like heck to stop. So that's not it.

A mushy pedal can be caused by several things:

Air in the lines (but you've bled, so that's not it)

Flex in brake lines (they expand under pressure, using up the pedal travel)

Bad master cylinder (fluid bypasses the piston)

Severely taper-worn pads (need alot of fluid movement to develop braking force)

Pad stuck in caliper (rusted, etc.)

Stuck caliper piston in front caliper: one is not moving, forcing the opposite one to deflect the rotor until the sticking piston's pad is contacted)

Stuck sliding caliper in rear - similar to above

And probably a few more things I've forgotten.

i think i have a similar problem... it takes one quick pump for me to get a firm brake pedal feel. ive tried bleeding and it didnt work. think it could be the vac lines to the booster system?

Again, low booster vacuum makes the brake pedal hard and the car is hard to stop. Either something is leaking, sticking or flexing, or there is air in the system.

If pumping the brakes improves the pedal feel, It's most likely air in the system, excessive run out of the rotors pushing the pads too far from the rotor and/or (as DaveW said) pads that worn to a taper agian pushing the pistons in too far when you release the brakes. If you hold constent pressure on the pedal and you can feel it slowly go down, it's likely the seals in the master cylinder leaking.

Wouldn't badly worn pads also increase pedal travel that improves when you pump it?

If the pads wear evenly (not at an angle), the caliper pistons just follow them, meaning the pedal travel will remain the same. The travel is made up by filling the piston bores with brake fluid from the reservoir. The reservoirs are made large enough so this is not a problem.