Prado 120 drivetrain slack

Does the handbrake have a two cables running underneath to the rear brakes. Also is this vehicle fitted with rear drum or disc brakes ???? If it has drum brakes on the rear, there is a small chance that either one of two things have happened and that is a broken cable to one of the rear wheels, or the cables have stretched over time to the point that it has so much slack that its not pulling the rear shoes onto the drum or the rear pads onto the disc sufficiently to hold it securely. Suggest you take it to your local garage and get them to check the cables. Other than that Toyotas are notorious for having lousy handbrakes. I carry a wooden chock to place in front or behind the wheel depending on which way the vehicle is facing. One other thing I do is select Lo range and shove it in first or reverse. Gauranteed not to move

Drew,
the handbrake is a drum inside the rear disks and should hold better than that. Sounds like it needs adjustment. Often "skipped" during servicing.
Should be the same as the 90series: Link here.