We just got back from Big South Fork (a lot of mountains) when we go home and pulled in to park the trailer we had no brakes. The peddle went completely to the floor.
I want to know if anyone else has experienced this after a long pull. Now my husband checked the brakes, no leaks and the mastercylinder was OK too.
After the truck sat for a few minutes we had brakes again.
We took it to a repair shop and this is what they told us...........
The shop said it could have had a vacuum by-pass and that it may never happen again. He told my husband that diesel engines work off of a different vacuum system than gas engines.
We don't like the odds on this and want to know if anyone out there has had this happen to them and if so how do we fix it.
We don't want to take a chance on the odds of it happening again...........

Welcome to the forum ..
Not having the truck to look at, the best you'll get over the Internet are guesses.

Diesels don't generate a vacuum like a gas engine. So they have to have a hydraulic booster or a vacuum pump running from a belt or internal engine parts... Someone else will know the Ford PS better than I.

As for guesses. Brake fluid absorbs water from the air over time. After a long down hill run with the brakes being used hard and hot (like descending Black Mountain) The water boils and creates gas bubbles (steam) in the brake system. Unlike brake fluid, the gas compresses and lets the petal go to the floor. This might be a likely cause of your lack of brakes... It also fits that when the system cools off it returns to normal.

When was the last time you had the brake system flushed and the fluid changed? Since 1999? Eight years ago ? Change the brake fluid ASAP...