This is the Critical version of the Gearbox PM Checklist — for production-critical equipment where unplanned failure means extended downtime or long lead times. For non-critical gearboxes where replacement outpaces troubleshooting, see the Standard version.
⚠️ Disclaimer: These tasks are guidelines only. They do not include lockout/tagout (LOTO), energy isolation, or other safety requirements. Review and verify suitability for your specific equipment and application. Add all required safety procedures per your company's policies and regulatory requirements before use. You are responsible for the safe and appropriate execution of all maintenance activities.
When a critical gearbox fails, the clock starts immediately. Lead times on replacement units can stretch weeks. Repair shops aren't waiting on you. Production doesn't stop calculating the cost while you're waiting on parts.
The failure usually didn't start that day. It started months earlier — with oil that looked a little dark, a vibration reading that crept up gradually, a bearing that was running warm and nobody wrote it down. The gearbox told you. Nobody listened.
This checklist is for the gearboxes you cannot afford to lose. It covers inspection, lubrication, mechanical condition, bearing monitoring, thermal imaging, and oil analysis. It is designed for maintenance teams building a real PM program — not one that exists to generate closed work orders.
Start with the full gearbox cluster here: Industrial gearbox PM fundamentals, failure modes, and what most programs miss.
How to Use This Checklist
Record findings with specificity. "OK" is not a finding. "Sight glass shows oil at midpoint, color normal, no sheen or particulate visible" is a finding. The difference matters when you're looking at the history six months later trying to figure out when the contamination started.
Trend everything that has a number. Temperature, vibration, oil analysis results, shaft runout — none of these mean anything in isolation. They mean everything in sequence. A vibration reading of 0.18 in/s RMS looks fine until you notice it was 0.09 in/s RMS eight months ago.
A bad finding sounds like: "Checked gearbox. Running okay." A good finding sounds like: "IR reading at input shaft housing: 187°F. Baseline from last PM: 162°F. 25°F rise flagged for follow-up. Oil sample submitted."
Date every entry. Sign every entry. If something is deferred, document why and when it will be addressed.
Field Checklist — Critical Tasks
These are the 10 highest-consequence tasks for field execution. Fast to run. Designed to catch the failures that announce themselves before they complete.
Visual Inspection
| Task | Freq | Type |
|---|---|---|
| Inspect gearbox exterior for oil leaks at all seals, gaskets, vent plugs, fill plugs, and drain plugs. Photograph and document any active leaks with location and severity. | Every PM | MEC |
| Check oil level via sight glass or dipstick. Compare to manufacturer fill specification. Record reading. Investigate cause if oil is consistently low between PMs. | Every PM | MEC |
| Inspect oil color and clarity. Dark (oxidation), milky (water contamination), or metallic-tinged oil (internal wear) requires immediate oil change and investigation. | Every PM | MEC |
Operational Checks
| Task | Freq | Type |
|---|---|---|
| Measure gearbox operating temperature at housing using calibrated IR thermometer. Record and trend. Elevated temperature (>20°F above baseline) indicates lubrication failure, overloading, or bearing degradation. | Monthly | MEC |
| Listen for abnormal noise during operation: whining (gear mesh), grinding (bearing), knocking (tooth damage), or rumbling. Record observations. Any new or changed sounds require follow-up. | Every PM | MEC |
| Inspect breather/vent plug. Confirm vent is open and unobstructed. Replace contaminated or damaged breathers. Pressurized gearboxes should maintain specified internal pressure. | Monthly | MEC |
Bearing Condition Monitoring
| Task | Freq | Type |
|---|---|---|
| Measure vibration at gearbox housing (drive end and non-drive end) in radial and axial directions using calibrated vibration meter. Record overall velocity (in/s RMS) and compare to ISO 10816 or site baseline. Elevations >25% above baseline warrant investigation. | Monthly | MEC |
| Perform infrared thermography scan of gearbox housing, input shaft, and output shaft areas. Flag hot spots. Document and compare to previous thermal baseline image. | Quarterly | MEC |
Oil Analysis / Lubrication
| Task | Freq | Type |
|---|---|---|
| Collect oil sample from drain port or sample valve for laboratory analysis. Submit for viscosity, oxidation level, water content, and wear metals (Fe, Cu, Al, Pb). Compare to previous results and flag deteriorating trends. | Semi-Annually | MEC |
| Verify output shaft-to-load alignment using dial indicator or laser alignment tool. Correct angular and parallel misalignment to within manufacturer tolerance. Record final alignment values. | Semi-Annually | MEC |
Reference Checklist — Full Task Library
Complete task library for maintenance managers building or auditing gearbox PM programs. Pick and apply based on equipment criticality, operating environment, and failure history.
Visual Inspection
| Task | Freq | Type |
|---|---|---|
| Inspect gearbox exterior for oil leaks at all seals, gaskets, vent plugs, fill plugs, and drain plugs. Photograph and document any active leaks with location and severity. | Every PM | MEC |
| Check oil level via sight glass or dipstick. Compare to manufacturer fill specification. Record reading. Investigate cause if oil is consistently low between PMs. | Every PM | MEC |
| Inspect oil color and clarity. Dark (oxidation), milky (water contamination), or metallic-tinged oil (internal wear) requires immediate oil change and investigation. | Every PM | MEC |
| Inspect mounting base and foundation for cracking, corrosion, or grout deterioration. Flag any structural concerns for engineering review. | Semi-Annually | MEC |
Operational Checks
| Task | Freq | Type |
|---|---|---|
| Measure gearbox operating temperature at housing using calibrated IR thermometer. Record and trend. Elevated temperature (>20°F above baseline) indicates lubrication failure, overloading, or bearing degradation. | Monthly | MEC |
| Listen for abnormal noise during operation: whining (gear mesh), grinding (bearing), knocking (tooth damage), or rumbling. Record observations. Any new or changed sounds require follow-up. | Every PM | MEC |
| Inspect breather/vent plug. Confirm vent is open and unobstructed. Replace contaminated or damaged breathers. Pressurized gearboxes should maintain specified internal pressure. | Monthly | MEC |
| Verify gearbox nameplate data matches current application requirements: ratio, service factor, input speed, output torque. Flag any discrepancies for engineering review. | Annually | MEC |
| Verify gearbox load conditions have not changed. Confirm duty cycle, operating speed, and connected load match original design basis. Escalate to engineering if changes have been made without review. | Annually | MEC |
Mechanical Inspection
| Task | Freq | Type |
|---|---|---|
| Inspect input shaft seal for leakage, cracking, or hardening. Check lip contact. Replace if leaking or oil tracking is present. | Quarterly | MEC |
| Inspect output shaft seal for leakage, cracking, or hardening. Check lip contact and surrounding area for contamination entry. Replace if degraded. | Quarterly | MEC |
| Measure input shaft radial runout and axial end float using dial indicator. Compare to manufacturer spec. Elevated readings indicate bearing wear or shaft damage. | Semi-Annually | MEC |
| Measure output shaft radial runout and axial end float. Document results and compare to previous readings and manufacturer tolerance. | Semi-Annually | MEC |
| Verify output shaft-to-load alignment using dial indicator or laser alignment tool. Correct angular and parallel misalignment to within manufacturer tolerance. Record final alignment values. | Semi-Annually | MEC |
| Inspect input coupling for wear, cracking, spider element condition (if elastomeric), or loose set screws/keyways. Replace worn elements. Verify coupling torque rating matches drive requirements. | Semi-Annually | MEC |
| Inspect output coupling or sprocket/chain connection for wear, backlash, or mechanical looseness. Verify drive component is properly keyed and secured. | Semi-Annually | MEC |
| Check all gearbox mounting bolts and base fasteners. Torque to manufacturer specification using calibrated torque wrench. Record torque values. | Quarterly | MEC |
| Inspect fill plug and drain plug threads and seating surfaces. Replace sealing washers or apply thread sealant as required. Confirm plugs are torqued to spec. | Annually | MEC |
Lubrication
| Task | Freq | Type |
|---|---|---|
| Collect oil sample from drain port or sample valve for laboratory analysis. Submit for viscosity, oxidation level, water content, and wear metals (Fe, Cu, Al, Pb). Compare to previous results and flag deteriorating trends. | Semi-Annually | MEC |
| Drain and replace gearbox oil at manufacturer-specified interval. Inspect drained oil for metal particles, shiny swarf, or sludge. Record oil type, viscosity grade, quantity, and date. Flush if contamination is found. | Annually | MEC |
Bearing Condition Monitoring
| Task | Freq | Type |
|---|---|---|
| Measure vibration at gearbox housing (drive end and non-drive end) in radial and axial directions using calibrated vibration meter. Record overall velocity (in/s RMS) and compare to ISO 10816 or site baseline. Elevations >25% above baseline warrant investigation. | Monthly | MEC |
Thermal Imaging Reference Points
| Task | Freq | Type |
|---|---|---|
| Perform infrared thermography scan of gearbox housing, input shaft, and output shaft areas. Flag hot spots. Document and compare to previous thermal baseline image. | Quarterly | MEC |
Program Administration
| Task | Freq | Type |
|---|---|---|
| Review complete gearbox maintenance history: oil changes, leak repairs, vibration trends, oil analysis results, and any reported abnormalities. Update maintenance plan based on findings. | Annually | MEC |
| Confirm spare parts availability for critical components: shaft seals, gasket sets, breather plugs, coupling spider elements, and oil fill. Update spare parts inventory if needed. | Annually | MEC |
Failure Modes This Checklist Targets
Lubricant Degradation and Contamination Oil that's broken down, contaminated with water, or carrying wear metals is no longer protecting gear teeth or bearings — it's accelerating their destruction. Oil analysis and visual checks catch this before the damage becomes structural.
Bearing Wear and Fatigue Gearbox bearings carry both radial and axial loads and are among the first components to show degradation through vibration and temperature rise. Monthly vibration trending and quarterly thermography catch bearing deterioration while options still exist.
Gear Tooth Wear and Surface Fatigue Pitting, spalling, and micropitting on gear tooth flanks develop gradually under load — often with no external indication until gear mesh noise or oil analysis metal content spikes. Operational sound checks and oil analysis are the primary detection tools.
Shaft Seal Failure Lip seals age, harden, and lose contact with the shaft. The result is oil loss, external contamination entry, and — in environments with particulate — accelerated internal damage. Seal inspections catch degradation before it becomes a leak and a contamination event simultaneously.
Misalignment Output shaft misalignment loads bearings and seals unevenly, accelerates gear tooth wear on one flank, and generates vibration that compounds every other failure mode already in progress. Semi-annual alignment verification is one of the highest-return tasks on any gearbox PM.
Fastener Loosening and Structural Degradation Gearboxes run under sustained dynamic load. Mounting bolts back off. Base grout cracks. A gearbox that's moving on its base is producing misalignment, fretting, and accelerated wear — and often nobody notices until the base has deteriorated enough to require a shutdown to repair.
Related Checklists
The standard version for non-critical gearboxes: Gearbox PM Checklist — Standard
For helical gear reducers specifically: Helical Gear Reducer PM Checklist — Critical
For bevel helical reducers: Bevel Helical Reducer PM Checklist — Critical (Bevel Helical Reducer PM Checklist — Critical)
If you're still working out why the gearbox failed in the first place: the failure modes and PM gaps that show up in every gearbox cluster
