I have a 2001 Ford F53 chassis, and my parking brake is a circular drum mounted on the driveline, just rearward from the transmission, and certainly not on my differential. Here is a photo of my parking brake, looking toward the front of the coach. You can see the black actuating cable approaching the brake assembly from the upper left, and the cable terminates in a clevis at the 6 o'clock position of the parking brake drum. That said, the holding power of the parking brake is absolutely terrible; I have accidently moved my coach in my driveway with the parking brake set full on; further, I have driven a mile or so with the brake only lightly set. (This is easy to do because the brake light is rather dim and can't be seen at all in full daylight.) Ford should provide a specification of the parking brake's capacity (perhaps defining that it will hold against the GVW on a slope of x degrees), but I have never found such a statement. Without such a statement, a Ford dealer has no guidance about just how bad your particular brake really is. I would have zero confidence that the OEM parking brake could hold on any incline. Since it is so easy for you to abuse this brake (driving with it on will glaze the pads at best and completely destroy the assembly at worst), I would always get in the habit of chocking all wheels if I had to park on any incline.