When should you adjust the rear brakes on a disc-drum brake system?

Adjusting the rear brakes on a disc-drum brake system should be done after releasing the parking brakes to ensure proper brake operation. When the parking brake is engaged, it can cause the rear brake shoes to remain extended against the drum, which may lead to an inaccurate assessment of the brake's clearance and performance.

Releasing the parking brakes allows the brake shoes to retract properly, giving a true representation of the adjustment needed. This prevents unnecessary stress or wear on the components and ensures that adjustments reflect the actual operation of the brakes under regular conditions.

Moreover, performing maintenance tasks such as checking brake fluid levels or inspecting brake pads before the adjustment process would not provide the necessary environment to accurately adjust the rear brakes. Hence, the correct procedure is to always begin any adjustments with the parking brakes released.