unless you have abs, they should lock up. of course, you want all 4 to lock up simultaneously, but sometimes with disc/drum combo configs, you get the front two to lock up first, or the back two (what you don't want, obviously, is either right or left side locking up without the other).

possibly air in the brake lines maybe? could maybe be a froze up or corroded caliper? 14k miles is not enough (well, shouldn't under normal conditions) to wear out pads or rotors.....and if they were worn out you would know it by the awful sounds or the vibration or shaking. did you try (sans trailer, that is) to lock them up, or will they not lock up at all? you'll know you have something amiss if one side locks up before the other.