The way this works is it is called parking brake shoes and there is a set of brake shoes inside the rear rotor. When you pull the brake, it pulls a cable which pulls a lever, which presses the shoes against the inside part of the rotor. This friction holds the vehicle in place. However, inside each rotor there are two shoes. One called the primary shoe and the other called the secondary. One of them holds the vehicle when the weight is trying to move the vehicle forward and the other holds the weight of the vehicle when it is trying to move rearward.
It holds one way and not the other because they are out of adjustment and when you pull the brake handle only one of the shoes in each rotor are making enough contact to hold the vehicle in place.
I attached the adjustment procedure but if they have not been inspected in a while, you probably want to take them apart and replace what is needed.
Let me know if you have any questions. Thanks
Images (Click to enlarge)
Tuesday, May 7th, 2019 AT 7:09 PM