Ford Truck Enthusiasts Forums - 5.4, brake pedal goes to the floor, with a whoosh sound, with engine running?

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5.4, brake pedal goes to the floor, with a whoosh sound, with engine running?

Pedal is firm, when engine is off. I have good fluid levels in master cylinder and nothing on the truck has been messed with in months. Truck ran fine 2 days ago, but started it yesterday and brake pedal, now goes to the floor. I checked the fluid level and its fine. Is this a brake booster problem or an ABS problem? I don't remember seeing any brake warning lights and the fluid level looks good.

I have been told, a bad booster will not cause the pedal to go to the floor, but I don't know??? I would greatly appreciate some help from one of you truck guru's... :)
Thanks guys!
TB

Has anyone ever suggested posting your year, model, chassis and fuel type in your questions here?

Quote:

Originally Posted by mach2race (Post 18722054)

but started it yesterday and brake pedal, now goes to the floor. I checked the fluid level and its fine.

Inspect the inside of all the wheels and underbody for signs of brake fluid leaking. A tiny leak will cause the low pedal and still take a while to lose a noticeable amount of brake fluid.