Drum Parking Brakes
Integral parking brake drum brake system's have similar characteristics. Instead of hydraulic pressure, mechanically operated parking brakes are controlled with a brake lever or pedal. Parking brake systems like the one in the illustration use a cable, a lever, and a strut to apply the parking brakes. A cable is attached to the lower portion of the brake lever and the upper portion is attached to a swivel or pivot on the secondary shoe. The lever pushes the rear shoe outward and the brake strut forces the forward shoe into the drum.
The secondary shoe is the shoe facing the rear of the vehicle. In the illustration you see that the parking brake strut is the member that acts upon the primary shoe, facing the front of the vehicle. These two parts (cable | strut) work together to apply both the secondary and the primary shoes with equal force.
As the driver engages the parking brake the cable pulls the lever forcing the secondary shoe in one direction and primary in the other. It does this by acting upon the brake strut located between the two. It's because this strut is located further down the lever arm than the swivel that its leverage forces the primary shoe outward.