If your vehicle is showing rear wheels locking up or dragging while driving, here are the most likely causes and the parts you'll need to fix each one.
The brake caliper piston or slide pins can rust and seize, preventing the brake pads from releasing after you let off the pedal. This causes constant friction, overheating, and dragging.
The protective sheath around the parking brake cable can crack, allowing water in that rusts the internal wire. When you release the handle, the cable stays stuck, keeping the rear brakes applied.
If the rear brakes were recently serviced, the star wheel adjuster or parking brake cable may have been set too tight. As the brakes heat up and expand during driving, they lock against the rotor or drum.
On vehicles with rear drum brakes or drum-in-hat parking brakes, the friction material can separate from the metal shoe, or a return spring can snap. The loose pieces wedge between the shoe and drum, locking the wheel.
The internal rubber lining of the flexible brake hose can deteriorate and collapse, acting like a one-way valve. It allows fluid pressure to apply the brakes but prevents it from returning, keeping the caliper locked.
A severely worn wheel bearing can overheat, melt, and physically weld itself together or collapse. This will cause the wheel to violently lock up or drag heavily while driving.
Lack of lubrication or extreme stress can cause the internal gears or bearings in the rear differential to shatter. The broken metal chunks wedge into the gears, instantly locking the rear axle.