Recently my rear brake line popped off and casued me to lose my rear brakes. So i put it on and bled all my brakes. Everything was all good for about two to three weeks. Now I have lost almost all my brake pressure. I jacked the truck up. Looked. No leaks. No loose hoses. Nothing. The resovoir is still full which confirms the no leak part. When I brake I have to press the pedal down to almost the floor to get any response. And I get my pressure there but not as much as if it was working fine. Im thinking my master cylinder is shot but want to be sure before I buy a 70 dollar part. By the way its a 1998 4 cylinder. Any and all help is appreciated. I hate brakes....

 

Sure the shoes in the drum are still setup good? A friend had the same problem, the shoes came off the rear cylinder, could not build pressure as they were basically pushing against nothing. Hard to explain but check the rears...

 

Definately pull the drums off and make sure everything is still in place and also look at the wheel cylinders. It could be your master cylinder but thats not very common for one to go out. Check the vacuum lines under the hood. Make sure the brake booster line is still connected at the booster and at the intake. Since your resovoir is still full it can be a number of things. Good luck man.