Rear brake question

[Jaysonb]

My truck is a 80 k10. If all of the rear brake components are in working condition, what is the action that keeps the rear brakes adjusted? (Like using brakes in reverse, or using parking brake) My rear brake system is new, including all of the parking brake components, and when I installed them the brakes were awesome. The brakes still work good, but I can tell that the back brakes are not as tight as when I manually adjusted them, when I installed them. Thanks for any input!