Brake problem, emergency

Had brakes and resonator repl. On our Nissan Maxima
Emergency brake handle worked before to hold the car. Now after getting back the emer. Brake doesn't hold as it has to be cranked all the way up and still
doesn't hold. Mech says the reason is the threads in the cylinder of the caliper are worn and they are slipping when the brake handle is operated. He says he hears the sound in the rear brake area. I hear it when i'm under the car and someone operates the
brake handle, above the resonator assy. And heat shield. This area is just under the front seat area.
Is the mech. Correct or could it be the cable popping out of it's position above the heat shield. Can't see the cable as it disappears under the body metal.
Thanks, Just want to know if I should repl. The calipers to cure the problem. Joe in Ill.