You might be missing some components
You might be missing some components or your adjuster has become unthreaded. The park brake system that brakes on the driveshaft typically uses a cable that goes to the park brake drum on the rear of the transmission. The cable (bear with my beer adleded memory) has a threaded portion at the park brake handle and at the drum mechanism. You could have a stripped nut on the handle as well if someone torqued it down real hard. Tighten the handle with the brake released (it may turn for quite a time, it's fine threaded) and see if that helps. Your could have a broken cable or as I stated above, stripped threads. The cables are available at the dealer, NAPA, CarQuest, or other medium duty parts sellers. Good Luck!