Rear brakes draging

Quick checks

1. Lift the rear off the ground, put in neutral, emergency brake off and turn each wheel by hand. What do you get? The wheel should turn freely and if adjusted properly you will hear slight rubbing of the drum to the brake shoes. Like a scratching noise.  (Many times the adjustment is incorrect, many times new shoes are adjusted to tight. Mechanics do this so that re-adjustment is not needed as quickly)

2. Make sure the emergency brake is adjusted properly and the cables work properly. Sometimes the cables will hang up. As soon as the e-brake is used one or both sides hang up. Again with the rear of the car in the air ( tires/wheels on) engage the e-brake, check that the wheels are holding, release the e-brake and check again. Maybe do this  several times as e-brake can hang up intermittently. 

3. Get a TSM ( Service manual) and check for the correct placement of all parts. Springs and adjusting cable are often installed incorrectly. Another part if installed backwards that can cause problems is the (parking brake "link" or called the "strut" or called the "push rod"). The return spring on this part is often installed on the incorrect side. Check the TSM for the correct location specific to your car.

4. Check the brake wheel cylinder. You may need to remove the brake shoes and springs. See if both wheel cylinder push rods are moving freely. Do this by hand, do not push on the brake pedal. As the wheel cylinder wears or begins to rust out the piston cup will start to turn slightly and catches the side of the wheel cylinder housing causing a binding issue. If there is any resistance from a smooth movement of the piston cup, remove the rubber boot and visually check the bore of the wheel cylinder.

 Some other things to check. 

Incorrect brake shoe size is a common problem. Usually the width is the issue. This will cause the drum to rub against the side of the brake pad and can cause the brake pad to hit against the backing plate. I have returned many new brake pads because they may have been packaged incorrectly. ( Wrong part, but the correct part number). It happens! 

Worn out springs may cause sloppiness in the brake parts, which can cause intermittent issues such as rubbing problems, premature wear of parts, etc.

Drum is out of round. Measure proper thickness and the drum is concentric.

Brake pads have uneven wear. ( Many causes, cheap pads, pad is separating from shoe, pad is not tight against the shoe, etc..  - visual check that all parts are built correctly and assembly is correct)

Just some quick thoughts for things to look at.