How do I fix a trans mounted brake assembly failure?

Per the paperwork that came with this Motorhome, this is a 1997 Ford-150 or F Series with a F-53 chasis ,class A Pace Arrow. 7.5 engine. It broke down, I could go in reverse and gear into low and neutral, but putting it into 2nd gear or Drive, it would not moved and make a loud clanking n rattling noise. A mechanic diagnosed it as a failed parking brake assembly.But would that make all that noise and cause the RV not be able to go into drive gear? The actual wording for that brake section is called-‘Cable-Actuated Transmission-Mounted Parking Brake Assembly. Sorry for the lengthy discription, just wanted to be more specific.Thanks for your reply🙂