Loosing Brake Pressure

When driving downhill, after about 10 seconds of having the brakes down, the pedel just drops(almost to the floor) anyone kno what could be my problem, and how i go about solving it?

Look at your master cylinder first. any wetness and it has to go. check your wheel cylinders next, pull the rubber back, any wetness and they need to go. (unless it's grease, but that is a different problem) Check your brake lines and the proportioning valve, they should also be dry. I have never seen a proportioning valve leak however.

Good luck and let us know how it turns out

Nate