Two years ago, I bought a '94 F150. The day I bought it, I stopped at a garage to inquire about renting a tow dolly (they were also a U-Haul franchise.) Up to that point, the truck drove and braked great.
They didn’t have any dollies, so I left. Upon stepping on the brake prior to engine start, the pedal went to the floor with NO resistance. Upon getting out, I noticed a large and spreading leak along the left frame rail, near the firewall (around where the proportioning valve is). I went in, said, “Oh, by the way…” and they fixed it properly to this day.
My question: are any “single point failures” possible in the hydraulic system beyond the master cylinder? I realize a bad master, or the pedal decoupling from the master…but I thought once you got past that point, you had two fully independent hydraulic circuits.
Did I encounter a “perfect storm” failure of two systems simultaneously, was one circuit previously inop, or what?