The best way to adjust the handbrake on these is at the handbrake shoe adjuster (barrel type adjuster on handbrake shoes),not at the handle lever inside the car.The handle lever adjustment needs to be backed off all the way, then the handbrake shoes need to be adjusted.This involves removing the rear calipers and disc rotors and turning the adjuster so the discs still turn freely when fitted and the actuation levers have minimal travel.Then the handbrake lever inside the car is adjusted.This will give you a good strong handbrake that shouldn't require adjusting for a while.Too many people take the quick way out and just keep adjusting the handle but this isn't the best way to do it because the levers on the handbrake shoes are at a bad angle for maximum leverage effect.
Hope this helps.