You are right the handbrake does not auto tighten. there is a blanking grommet in the bottom of the rear disk back plate that allows access to the adjuster. with the wheel off the ground tighten each one until the wheel binds with the handbrake two clicks up. the hand brake on GV's is poor at the best of times so don't expect too much. The cable in the cabin should not need tightening and definitely shouldn't be used to adjust the brakes.