Absoutely do _NOT_ ajust the cable under the car, this is only if the cable streaches, this will NOT help you if the auto ajusters are not functioning correctly. The way I do it is to remove the rear wheel, and the drum, then remove the drum inspect everything (you should really do this anyway) and then adjust the rachet wheel, if it does not click it needs servicing, if you cannot see how this is done take it to someone who does, as when these fail the whole balance of the breaking system fails.