Copyright Goodheart-Willcox Co., Inc. Heavy Equipment Power Trains and Systems 592 Preload and Endplay As in most transmissions, shims are used to set the preload or endplay in final drives. A dial indicator is used to check the pinion shaft’s end- play, Figure 17-31. If the endplay needs adjustment, the shims need to be changed to a different thickness. See Figure 17-32. Failure A nalysis Components fail for a variety of reasons. Identifying the root cause of the failure is crucial in order to avoid repeat failures. Failures can be the result of improper use or maintenance, contamination, or manufactur- ing mistakes. Wear, fracture, distortion, and corrosion can occur. Wear Components can wear, causing the outer surface of the component to erode. There are three common types of wear failures: • Adhesive wear. • Abrasive wear. • Corrosion wear. Adhesive wear occurs when two adjacent component surfaces con- tact each other. Friction between two heated components results in the two surfaces welding to each other. As the components attempt to move, material lifts off both components, tearing off or transferring material. Adhesive wear causes a component to fail quickly. Adhesive wear can occur due to lack of proper heat treatment. When a component is heat treated, the outside surface hardens and becomes wear-resistant. A component that lacks proper heat treatment experi- ences adhesive wear but will not be discolored if it was properly lubri- cated. See Figure 17-33. Pro Tip A file can be used as a hardness gauge. If the file digs into the component and scratches the metal when only light force is applied, the component is too soft and lacks heat treatment. If the file skates across the surface with- out digging in, the component has a hardened surface. Shims A B Goodheart-Willcox Publisher Figure 17-31. A dial indicator is used to check the pinion shaft’s endplay. Goodheart-Willcox Publisher Figure 17-32. If final drive pinion shaft endplay needs adjustment, the shims are changed to a different thickness. Goodheart-Willcox Publisher Goodheart-Willcox Publisher Figure 17-33. A component that exhibits adhesive wear and has not been properly heat treated will not be discolored if it has proper lubrication. A— This bevel gear lacked proper heat treatment and shows adhesive wear. B—The outside race to the tapered roller bearing lacked proper heat treatment, causing it to exhibit adhesive wear. The inside race and tapered roller bearings show little wear because they were properly heat treated.