Before starting the inspection, review the background information and service history with the contact person. Then interview those involved in the design, installation, operation, maintenance, and failure of the gearbox. Encourage them to tell everything they know about the gearbox even if they feel it is not important.
After completing the interviews, explain your objectives to the technician who will be working with you. Review the gearbox assembly drawings with the technician, checking for potential disassembly problems.
Visual examination. Before disassembling the gearbox, thoroughly inspect its exterior. Use an inspection form as a guide to ensure that you record important data that would otherwise be lost once disassembly begins. For example, the condition of seals and keyways must be recorded before disassembly. Otherwise, it will be impossible to determine when any damage may have occurred to these parts. Gear tooth contact patterns should be taken before completely disassembling the gearbox (see next section).
After the external examination, disassemble the gearbox and inspect all internal components, both failed and undamaged. Examine closely the functional surfaces of gear teeth and bearings and record their condition. Before cleaning the parts, look for signs of corrosion, contamination, and overheating.
After the initial inspection, wash the components with solvents and re-examine them. This examination should be as thorough as possible because it is often the most important phase of the investigation and may yield valuable clues. A low power magnifying glass and pocket microscope are helpful tools for this examination.
It is important to inspect the bearings because they often provide clues as to the cause of gear failure. For example:
• Bearing wear can cause excessive radial clearance or end play that misaligns the gears.
• Bearing damage may indicate corrosion, contamination, electrical discharge, or lack of lubrication.
• Plastic deformation between rollers and raceways may indicate overloads.
• Gear failure often follows bearing failure.
