I have a 1982 f-150 and when i press the brakes at first they are fine but if i let off just a little they go farther down before they catch and if i hold them even not letting off evetually they go to the floor anyway. If you let it come back up by itself or pull it up with your foot it is fine till you let off of it and then the same thing. What would cause this? Thank for any help!

 

2000 XLT SD SC 7.3 DIESEL 4X4 AUTO.

Sounds to me like the Master Cylinder. Check it quick ! ! !

 

Hay bud was the fluid level down when you checked it? Have you replaced your master cylinder? Don't over look the vacuum buster!