The parking brake on the Pinto is cable accuated. Lifting the lever pulls on a cable which in turn pulls on a lever expanding the rear brake shoes. Most likley your problem is a rusted brake cable. This happens when the parking brake is not used very often, very comon on automatic transmission cars as most people just put in park and not engage the parking brake.To be safe replace it with a new one.

Look under the car below the brake handle area above the drive shaft to see if the cable is connected to the horseshoe  shaped bracket attached to the brake mechanism.

It might also be the brake hardware on the drums. A good way to check is jack the car up, use jack stands to support the rear end and remove one wheel and drum. Get a good manual and see if everything is there, on that side, and than, of course check the other side. I'm betting it's not the cable but the hardware that makes everything work..  I have had to replace the hardware on two cars. If you get a brake hardware kit you should have every thing you need to fix the problem, just the hardware nothing else IE no brake shoes , cylinder etc...