1. Description and scope of the problem

This guide covers the symptoms of abnormal noise and vibration on gear reducers (cylindrical, bevel, epicyclic) used in the aerospace and energy industries. These symptoms often indicate impending failure. The severity classification is critical if it is accompanied by a rapid increase in temperature or metal debris in the oil.

2. Safety Precautions

WARNING: Danger of stored energy and rotation. Before any intervention, strictly apply the lockout procedures (LOTO). Ensure equipment is electrically and mechanically isolated. Use cut-resistant gloves and protective glasses. Never open a gearbox housing under pressure or under load.

3. Necessary diagnostic tools

Tool	Specification/Model	Range/Measurement	Objective
Vibration analyzer	Multi-channel FFT, min 20kHz	0.1 - 50 mm/s	Detection of characteristic frequencies (meshing, bearings)
Thermal camera	Resolution 320x240, ±2°C	-20°C to +500°C	Identification of hot spots (friction, overload)
Thickness Gauge/Comparator	Accuracy 0.01 mm	0 - 25mm	Measurement of backlash
Oil analyzer	Approved laboratory	Spectrometry, ferrography	Detection of wear particles (Fe, Cu, Al)

4. Initial Checklist

Observation	Action	Registration
Alarm history	Consult the supervision system	Type and frequency of alerts
Operational conditions	Measure load, speed, temp	Nominal vs. Current Values
Recent changes	Check maintenance logs	Lubricant, alignment, parts changed
Apparent leaks	Visual inspection	Location and leak rate

5. Systematic diagnostic flow

Step 1: Spectral analysis of vibrations
- If peak at the meshing frequency (GMF) → Check the sidewalls for wear or poor contact.
- If peaks at bearing frequencies (BPFO, BPFI) → Probable bearing failure.
Step 2: Oil analysis
- Presence of ferrous particles (> 50 µm) → Severe gear wear.
- Presence of non-ferrous particles (Cu) → Wear of bearing cage or worm bronze.
Step 3: Physical Inspection
- Excessive play measured → Tooth wear or shaft loosening.
- Localized overheating → Faulty lubrication or poor alignment.

6. Defect-cause matrix

Symptom	Probable causes	Testing	Expected result if confirmed
High-pitched noise (whistling)	Bad alignment, sidewall wear	FFT analysis (GMF peaks)	Increased vibration level to 1x GMF
Low noise (rumbling)	Bearing failure	FFT analysis (peak bearing frequencies)	High levels at BPFI/BPFO frequencies
Erratic vibrations	Imbalance, excessive play	Backlash measurement	Clearance outside manufacturer tolerance

7. Root cause analysis

Tooth wear (pitting/spalling):Caused by cyclical overload or inadequate lubrication. Confirm by oil analysis (Fe particles). Damage: destruction of the teeth over time.
Bearing failure: Caused by fatigue, contamination or improper assembly. Confirm by spectral analysis (bearing frequency peaks). Damage: shaft blocked.

8. Resolution procedures

Replacement of bearings: Respect the adjustment tolerances (eg: H7/p6). Check internal clearances after assembly.
Adjusting the clearance (backlash): Adjust the adjustment shims according to the technical specifications of the gearbox. Tighten to the recommended torque (e.g.: 150 Nm ± 5%).
Verification: After repair, carry out an empty test for 2 hours, followed by a vibration analysis for validation.

9. Preventive measures

Cause	Strategy	Method	Interval
Oil contamination	Filtration and analysis	Oil spectrometry	Quarterly
Rolling fatigue	Predictive maintenance	Vibration analysis (FFT)	Monthly

10. Spare parts and components

Description	Specification	Replacement	Category
Tapered roller bearing	Class P5, waterproof	At the sign of fatigue	UNITEC-D-ROU
Shaft seal (fpm)	Resistance 200°C	At each drop	UNITEC-D-JOINT

To order your certified spare parts, visit: https://www.unitecd.com/e-catalog/

11. References

ISO 10816-3: Evaluation of machine vibrations.
NF ISO 13372: Condition monitoring and diagnostics of machines.
UNITEC-D manufacturers’ technical manuals.