Halderman: I think there is a terminology problem with your comments and question. Before 1967 when there was just a single piston-type master cylinder, the mechanical braking system that applied the rear brakes was called the emergency brake. The standard that this system had to perform was to stop the vehicle within a specified distance using the emergency brake alone.
After 1967, this system was called the parking brake and the standard required the vehicle to be held without moving on an incline. The parking brake applies the brake shoes mechanically using a cable instead of force from the hydraulic brake system.
The parking brake system has to use a separate system from the system that is used to apply the standard brakes, which are called the service brakes. The parking brake cable, operated by either a hand lever or a foot pedal, can apply the disc brake piston mechanically or a separate small drum brake inside the “hat” of the rear disc brake rotor.
Apparently your friend had a failure of the base brake system and she was smart enough to get the vehicle stopped using the parking brake. She should have stopped driving the vehicle and had it towed to a shop for repairs instead of driving it further however.
Submit questions to jim@jameshalderman.com or follow him on Twitter @jameshalderman, or write to: Wheels, Marketing Publications Department, Dayton Daily News, 1611 S. Main St., Dayton OH 45409.
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