loss of pedal pressure mid stopping

[sab24711]

98 ranger with a 96 5.0 with over 50,000 miles since the swap
pretty much what the title says. during braking, the pedal went to the floor and a complete loss of braking ensued. I wasn't driving the truck when it happened so I'm not completely sure if the abs played a role in the situation. I recently replaced the front brakes and rotors and have also driven the car for a few weeks and nothing like this has happened to me and I know the person driving wouldn't lie about it. no signs of a leak or low fluid, any help would be appreciated

 

[Uncle Gump]

I've had it happen to me... and seen it on a few customer vehicles in the past. It's a master cylinder. Work flawlessly... then nothing. I think a piston seal rolls and pedal goes to the floor. On the way up the seal gets back into position the works until it happens again. Chances are... you will see some fluid loss between the master and the booster too.

 

[91stranger]

Whenever this happens to me it is due to a rusty brake line, normally at the rear axle. I live in Ohio so if brake lines are over 10 years old they start to rust and can get pinholes that can cause a soft pedal but not show leaks unless you physically see the leak when the brakes are applied. Have you tried having someone putting a lot of pressure on the brake pedal while you scroll around the brake lines? Wouldn't hurt. I'd rather replace a brake line than a master cylinder.