Final answer:
The backing plate should be replaced if shoe contact areas are worn past the manufacturer's specifications, typically beyond 0.060 inches.
Step-by-step explanation:
The backing plate should be replaced if the shoe contact areas (pads or ledges) are worn more than is specified by the manufacturer. The specific measurement for when a backing plate should be replaced may vary depending on the vehicle model and the manufacturer's specifications.
However, a general rule of thumb in the automotive industry is that if the wear exceeds 0.060 inches (1.5 millimeters), the backing plate should be considered for replacement. When these contact areas are excessively worn, it can lead to brake shoe misalignment.
It is misalignment and uneven braking pressure, potentially causing brake system failure and compromising vehicle safety.