Why do rear brakes grab

Parking brake cable rusted in the partially-applied position or they're adjusted too tightly. Axle grease, fingerprint grease, or other contaminants on the linings. Longer linings incorrectly installed toward the front of the truck. Grooves worn in the backing plate allowing the shoes to hang up. Height-sensing proportioning valve misadjusted, disconnected, or a sadly misinformed owner installed a lift kit.