The rear brake drums must be removed in order for the shoes may be inspected and measured for remaining thickness. Use a cloth dampened with water to wipe down the components or use an aerosol brake cleaner. Do not use a dry brush or air to clean the shoes. Measure the friction material (not the backing plate) at the thinnest point. Refer to the Brake Specifications chart for minimum thicknesses.
NOTE: It is a characteristic of brake shoes to show slightly uneven wear or for each shoe to wear differently. A shoe may have very different thicknesses at opposite ends; if the rest of the system is in good condition, this is not a sign of a problem.