Since you have parking brakes intregal with the service brakes I would try the following: Raise drive wheels off the ground (blocks under upright & full tilt forward should accomplish this), engine running, trans in forward, bring wheels to stop w/service brake & while holding brake shift trans into reverse & release brakes- see how free wheels are to turn in reverse. If they stick, put trans in forward again & then put trans in nuetral & let wheels stop rotating on their own. Once wheels stop rotating- shift into reverse & check how free wheels are to trun in reverse again. If they still tick I would back off the brake adjusters & do both tests again. I've seen brake shoe return springs break inside the drumn assy & this can allow a brake shoe so stay out & drag in one direction- hope this helps.