for the past day every few times i hit the brake the pedal goes about halfway before it grabs, if i let off and hit them again they are fine and hold pressure... not loosing brake fluid at all so im not sure whats causing it... oh btw 92 f250 7.3 idi HELPPP PLEASE

 

Most likely air in the lines. You probably need to bleed the brakes.

 

Could be air in the lines, I would def check that first. Could also be an excessively worn master cylinder allowing fluid to leak by the pistons.