So this morning I do my commute to work on a high speed highway, go to surface roads, stop lights, turns, etc, and pull into the company parking lot.
I hit the brakes to slow down a little in the lot, I was not going fast anyway, and the pedal goes to the floor.
WTF? Pump and I have a little braking power so I back into the parking spot get out and open the hood. Master cylinder reservoir is a little low.
I suspect a blown brake cylinder. I look under the truck and there is brake fluid running down the backing plate on the left rear-
I must have blown out a wheel cylinder on that last stop. There we NO warning of an issue before this happened. 
I was extraordinarily fortunate it happened this way and not when I was stopping from 70 mph only minutes before..
Tow truck is on the way to bring me home - I waited until the end of the work day to do that part, no rush.
How old is the truck? Shouldnt a dual circuit master (in most stuff since like 1967) have at least kept pressure in the fronts?
Very nice place to have a brake issue, I agree!
In reply to jharry3 :
Has little to do with drum brakes and everything to do with no dual circuit system. Disk brakes can blow out a seal too.
Early disk brake systems are just as vulnerable.
When one half of a dual circuit fails, there will likely be brakes somewhere down there by the floor. You do have a series of potential problems, though- Was the pedal a bit low before? Gonna be way low now. Is the master cylinder 20 years old with a layer of crap on the unused portion of the bore? Gonna be sticky, or damaged immediately. Are you an old guy with three layers of floor mats jammed under the pedal? Might bottom out before you commence to stopping.
From his profile page it's a Ford Ranger, which certainly would have a dual circuit master cylinder.
I check his profile page as well which showed a ford ranger. I’m my experience of having old slightly beater cars once one circuit craps out the initial pedal drop can push the master cylinder piston past it’s normal travel into a crapped up bore tearing the seals.
So word of advice for what it’s worth is due both wheel cylinders, the rubber hose, and the master cylinder. It’s cheap insurance for down the road.
