I have a 1998 Ram 2500 V-10. I got in it to go to town and the brake goes to the floor. Checked the whole truck and no fluid leaks. I bought a new master cylinder, replaced it after bench bleeding it. Bled it at lines after installation. The brake pedal still goes to the floor. What is going on? Proportioning valve? ABS? Thanks

 

Did you check the brake line running along the frame next to the gas tank? They are known to rust out and burst. You may not see the fluid because the frame catches it before it finds a way down to the ground.

 

I did not look at that specifically. I could not find any wet spots, and I am not losing

 

Rear line won't necessarily put fluid on the ground right away. Lots of places for it to pool, and wait til you are moving to run off.