For production-critical gearboxes where unplanned failure means extended downtime or long lead times, see the Gearbox PM Checklist — Critical.
⚠️ 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.
Gearboxes don't announce their failures. They drip, heat up, get loud, and slowly turn into expensive scrap while their PM records show nothing but checkmarks. The oil goes dark. The seals start to weep. The mounting bolts work loose from a vibration nobody logged. By the time production notices something is wrong, the damage is already months old.
This checklist covers the standard preventive maintenance tasks for industrial gearboxes used in non-critical applications — equipment where replacement is a reasonable option and extended troubleshooting is not the priority.
For a complete overview of gearbox failure modes and how a PM program should address them, see industrial gearbox preventive maintenance fundamentals.
How to Use This Checklist
Write down what you find — not just whether something passed or failed. "Slight weeping at input shaft seal, no active drip" is a finding. "Checked — OK" is a checkbox. The first one gives the next tech something to compare against. The second one is noise.
Record oil level readings with specifics: sight glass at 3/4, topped off with 2 oz of ISO 220 gear oil. Record abnormal noise observations with context: low-pitched whine on startup, clears after 2 minutes of operation. Trend those readings over time. A gearbox that needs topping off every PM cycle has a leak that hasn't been found yet.
If a task reveals something outside normal range, write a work order. Don't carry the finding in your head.
Visual Inspection
Field Checklist — Critical Tasks
| Task | Freq | Type |
|---|---|---|
| Inspect the gearbox exterior for oil leaks at seals, gaskets, and drain plugs. Note any wet or stained areas. | Every PM | MEC |
| Check oil level via sight glass or dipstick. Top off with correct oil type and viscosity if low. | Every PM | MEC |
| Inspect all vent/breather plugs for blockage or damage. Clean or replace as needed. | Monthly | MEC |
Reference Checklist — Full Task Library
| Task | Freq | Type |
|---|---|---|
| Inspect gearbox exterior for oil leaks at seals, gaskets, vent plugs, and drain plugs. Note location and severity. | Every PM | MEC |
| Check oil level via sight glass or dipstick. Compare to manufacturer fill spec. Top off with correct oil type and viscosity if low; investigate cause if repeatedly low. | Every PM | MEC |
| Check oil condition by observing color and clarity. Dark, milky, or metallic-tinged oil indicates contamination or internal wear — schedule oil sample or change. | Monthly | MEC |
| Inspect breather/vent plugs for blockage, damage, or missing plugs. Clean or replace to prevent pressure buildup. | Monthly | MEC |
Operational Checks
Field Checklist — Critical Tasks
| Task | Freq | Type |
|---|---|---|
| Listen for abnormal noise during operation — grinding, whining, or knocking. Tag for further inspection if found. | Every PM | MEC |
Reference Checklist — Full Task Library
| Task | Freq | Type |
|---|---|---|
| Listen for abnormal operating noise: grinding, whining, knocking, or rumbling. Compare to baseline. Tag for follow-up if noise has changed. | Every PM | MEC |
| Check gearbox operating temperature with IR thermometer. Compare to nameplate or baseline. Elevated temperature may indicate lubrication failure, overload, or bearing wear. | Monthly | MEC |
| Check for unusual vibration at gearbox housing using a vibration pen or handheld meter if available. Log reading and compare to previous values. | Quarterly | MEC |
Mechanical Inspection
Field Checklist — Critical Tasks
| Task | Freq | Type |
|---|---|---|
| Check all mounting bolts and foundation fasteners for tightness. Torque to spec if loose. | Quarterly | MEC |
| Inspect input and output shaft seals for leakage or wear. Flag for replacement if leaking. | Quarterly | MEC |
| Check coupling or sprocket connection at input and output shafts for wear, looseness, or misalignment. | Quarterly | MEC |
Reference Checklist — Full Task Library
| Task | Freq | Type |
|---|---|---|
| Inspect input and output shaft seals for leakage, cracking, or lip wear. Replace if leaking or degraded. | Quarterly | MEC |
| Check input and output shaft for radial play (wobble) and axial play (end float). Excessive movement indicates bearing wear. | Quarterly | MEC |
| Inspect coupling or sprocket at input and output shafts for wear, cracking, or looseness. Verify set screws or keyways are secure. | Quarterly | MEC |
| Verify shaft-to-load alignment at output. Correct if misalignment exceeds manufacturer tolerance to reduce bearing and seal load. | Semi-Annually | MEC |
| Check all mounting bolts and base fasteners for tightness. Torque to spec. Inspect mounting pad or base for cracking or corrosion. | Quarterly | MEC |
Lubrication
Field Checklist — Critical Tasks
| Task | Freq | Type |
|---|---|---|
| Drain and replace gearbox oil per manufacturer interval. Record oil type, quantity, and date. | Annually | MEC |
| Inspect oil fill and drain plugs for condition and proper installation. Replace sealing washers if worn. | Annually | MEC |
Reference Checklist — Full Task Library
| Task | Freq | Type |
|---|---|---|
| Drain and replace gearbox oil per manufacturer-specified interval. Record oil type, viscosity, quantity, and date of change. Inspect drained oil for metal particles. | Annually | MEC |
| Collect oil sample for laboratory analysis if condition monitoring program is in place. Submit for viscosity, wear metals, and moisture content. | Semi-Annually | MEC |
| Inspect drain plug and fill plug condition. Replace sealing washers or thread sealant if showing signs of leakage. | Annually | MEC |
| Review gearbox maintenance history for recurring leaks, oil consumption trends, temperature spikes, or previous repairs. Adjust PM frequency or tasks as warranted. | Annually | MEC |
Failure Modes This Checklist Targets
Lubricant degradation and contamination. Gear oil breaks down from heat, moisture, and accumulated wear metals — and once it goes, it takes internal components with it. Catching dark, milky, or metallic-tinged oil before the next change interval is the whole game.
Seal failure and oil loss. Shaft seals are the most common leak point in any gearbox. They wear, harden, and crack — especially when they're exposed to misalignment, overpressure from a blocked breather, or oil that's been in service too long. Leaks that get ignored become fires.
Breather blockage. A plugged breather creates internal pressure that accelerates seal failure. Nobody talks about it until the oil is on the floor and the seals are already gone. Takes 30 seconds to check. Takes three hours to clean up when it's missed.
Bearing wear. Shaft play and abnormal noise are the field-level indicators. Radial wobble and axial float don't appear suddenly — they develop over time and get louder if the trend is ignored. Catching them during a quarterly check costs nothing. Missing them costs a full rebuild.
Misalignment-induced overload. Output shaft misalignment puts constant side-load on bearings and seals. The gearbox looks fine. The PM records look clean. The bearing is burning hours off its service life every shift. Alignment verification stops that.
Mounting looseness and structural fatigue. Vibration works fasteners loose and cracks baseplates over time. Loose mounts amplify everything else — vibration increases, alignment degrades, and the failure cascade accelerates. Torquing mounting bolts is a five-minute check that earns its time back every PM cycle.
Related Checklists
The critical version of this checklist for production-essential gearboxes: Gearbox PM Checklist — Critical
Checklists for specific gearbox types:
Standard helical gear reducer PM tasks
Standard bevel helical reducer PM tasks
For the failure modes behind these tasks: Why gearboxes fail and what PM checks prevent it
