Inspecting Springs and Wheel Bearings for Corrosion, Overheating and Wear

Spring Inspection Procedures

It is essential that any exposed springs are carefully inspected for evidence of corrosion or overheating. Corrosion typically develops on static springs and reduces their load-carrying capability. When a spring subjected to cyclic loading becomes corroded, the combined effects of fatigue and corrosion result in a significant reduction in fatigue strength.

Overheating can be identified by blistering or deterioration of the surface protective coating and, in severe cases, by a discoloration of the metal caused by loss of temper. If overheating is detected, the spring must be considered unserviceable for its intended function.

Springs must be checked in accordance with specified figures or graphs. Some inspections are carried out at prescribed intervals, while others are performed on an opportunity basis, such as when a brake caliper is dismantled for overhaul.

Common Spring Checks

The most common inspection performed on a coil spring is a static length measurement. Load-versus-deflection checks are carried out on springs used in critical applications. These tests are performed using a dedicated test rig that applies compressive, tensile, or torsional loads, with instrumentation indicating the corresponding load and deflection values.

Any spring that fails to meet the required criteria is removed from service and replaced with a serviceable unit. 9275

Wheel Bearing Inspection

Once cleaned, the wheel bearing is inspected. There are many unacceptable conditions of the bearing and bearing cup, which are grounds for rejection. In fact, nearly any flaw detected in a bearing assembly is likely to be grounds for replacement.

Conditions That Cause Rejection

Common conditions of a bearing that are cause for rejection are as follows:

• Galling: caused by rubbing of mating surfaces. The metal gets so hot it welds, and the surface metal is destroyed as the motion continues and pulls the metal apart in the direction of motion.
• Spalling: a chipped away portion of the hardened surface of a bearing roller or race.
• Overheating: caused by lack of sufficient lubrication, which results in a bluish tint to the metal surface.
• Brinelling: caused by excessive impact.
• False Brinelling: caused by vibration of the bearing while in a static state.
• Staining and surface marks: located on the bearing cup as grayish black streaks with the same spacing as the rollers, caused by water that has gotten into the bearing.
• Etching and corrosion: caused when water and the damage caused by water penetrate the surface treatment of the bearing element.
• Bruising: caused by fine particle contamination, possibly from a bad seal or improper maintenance of bearing cleanliness.

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