Hi, i am sending you the proper procedures for adjusting the parking brake system. If after adjusting them they still don't seem to hold the vehicle then verify that when you set the parking brake with the handle you can actually see it expanding the brake shoes. If the brake shoes do not expand then the problem would be in the cables and handle. If the shoes do expand make sure the mating surface on the drum part of the rotor is clean, smooth and dry.
I hope this information is helpful and if so please choose to accept.
ADJUSTMENT - REAR DRUM IN HAT PARK BRAKE (ROTOR REMOVED) Under normal circumstances, the only time adjustment is required is when the shoes are replaced, removed for access to other parts, or when one or both rotors are replaced.Adjustment can be made with a standard brake gauge or with adjusting tool. Adjustment is performed with the complete brake assembly installed on the backing plate.CAUTION: Before adjusting the park brake shoes be sure that the park brake pedal is in the fully released position. If park brake pedal is not in the fully released position, the park brake shoes can not be accurately adjusted.