My parking brake is not effective.(Camaro IROC-Z with rear disc)

What is the best tips ?

This procedure :
‘…However, fixing it yourself should be relatively easy. The rear wheels are removed, and there is a nut on the back side of the brake caliper that holds the parking brake lever. Remove the nut, lever, and soft grommets. Put a large washer over the shaft to act as a spacer, and then put a wrench on the hex of the shaft, and tie it down with the nut. Turn the wrench to back the brakes off. After a while, this will over travel, as if there was a one way clutch. Tighten the shaft to see where the hex is when the pads are tight agains the rotor. If it is in a spot that the parking brake lever will fit, and turn about 1/3 of its travel to tighten apply the brake, then it is good. If not, try again.
This will remove some of the brake pedal slop also. It's supposed to be self-adjusting (apply parking brake thirty times), but it is common for it not to work’’

Or I buy Rear Brake Caliper Actuator Kit # 18019028 ?