1. Problem description and scope
Gear noise and abnormal vibrations are primary indicators of progressive wear or acute defects in drive components. This guide addresses symptoms such as high-frequency whining (gears), grinding noises (rolling bearings) and knocks (damaged teeth). The diagnosis is based on the DIN ISO 10816 (vibration measurement) and ISO 4406 (oil cleanliness classes) standards. This guide is designed for maintenance professionals in the DACH manufacturing industry who need to identify and repair critical or serious gearbox damage.
2. Safety instructions
WARNING: Before diagnosing the transmission, the system must be switched off in accordance with the applicable LOTO (Lockout/Tagout) procedures and secured against unauthorized reconnection. Gearbox housings can exhibit high temperatures after operation. Pressurized oil can cause serious burns. Always use the protective equipment (PPE) prescribed for the risk assessment. Be aware of stored energy in spring-loaded components or load on the transmission output.
3. Diagnostic tools
| Tool | Specification/Model | Measuring range | Purpose |
|---|
| Vibration analyzer | FFT analyzer, >10 kHz | 10Hz - 20kHz | Identification of defect frequencies |
| Thermal imaging camera | Measuring range -20 to +500°C | Accuracy ±2°C | Localization of overheating (bearings/gears) |
| Dial gauge with tripod | Resolution 0.01mm | 0-10mm | Measuring the tooth backlash |
| Oil sample kit | ISO 4406 compliant | Particle counting | Analysis of metal debris |
4. Initial checklist
| Checkpoint | Observation | Record |
|---|
| Operating condition | Load, speed, operating time | Documentation in fault list |
| Environment | temperature, humidity | Note reference values |
| Oil temperature | Measurement at the housing/drain | Comparison with target value |
| History | Last oil change, last repair | Check maintenance log |
5. Systematic diagnostic flowchart
- A. Symptom: High vibration level (> 4.5 mm/s)
- Check 1: Frequency Analysis (FFT).
- IF 1x speed: Probably unbalance or alignment error.
- IF bearing defect frequencies (BPFO/BPFI): Bearing worn/defective.
- IF Tooth meshing frequency: Gear problem (wear/misalignment).
- B. Symptom: Grinding noises
- Check 1: Check oil sample for metallic abrasion.
- IF Metal abrasion (ferromagnetic) present: bearing ring damage or tooth breakage.
- IF no metal abrasion: Possible resonance or cavitation (rare in gearboxes).
- C. Symptom: Knocking/beating noises
- Check 1: Check tooth backlash.
- IF Backlash out of tolerance (DIN 3967): Likely tooth damage or housing deformation.
6. Error-cause matrix
| Symptom | Probable cause | Diagnostic test | Expected result |
|---|
| Whining | Backlash incorrect | Dial gauge | Game > Tolerance |
| Grinding | Bearing defective | Vibration (FFT) | Increased bearing frequencies |
| Knocking | Tooth root fracture/pitting | Oil sample/visual | Large metal particles |
7. Root cause analysis
Rolling bearing wear
Wear on rolling bearings usually occurs due to inadequate lubrication or overloading. Diagnosis is made through frequency analysis. BPFI/BPFO frequencies are critical. If left unaddressed, this will result in locked bearings and catastrophic gearbox damage.
Tooth flank contact pattern error
Caused by incorrect alignment (shaft misalignment). Confirmation by blueprint (dye). Leads to one-sided wear and risk of breakage.
8. Step-by-step repair procedure
- Dismantling: Empty the housing. Remove seals. Check bearings and shafts for wear.
- Adjust the tooth flank backlash: Place the dial indicator on the tooth flank, fix the shaft, measure the backlash. Adjust adjusting washers according to OEM specifications (e.g. 0.05-0.15 mm).
- Bearing change: Press in bearing with a defined seat (tolerance h6/K7).
- Verification: After assembly, test run without load for 30 minutes. Measure vibrations again (limit value < 2.8 mm/s for new measurement).
9. Preventive measures
| Cause | Prevention strategy | Monitoring method | interval |
|---|
| Lubrication | Oil change/filter replacement | Oil analysis | Every 2000 Btr.-hours |
| Normal wear and tear | Condition monitoring | Vibration | Continuously / Monthly |
10. Spare parts and components
| Description | Specification | Change interval | Category |
|---|
| Rolling bearings | DIN 625/630 | In case of defect/wear | Storage technology |
| Gear oil | CLP220 | Regular | Operating resources |
| Gasket set | NBR/FKM | When dismantling | Sealing technology |
For your spare parts requirements, visit: https://www.unitecd.com/e-catalog/
11. References
- DIN ISO 10816-3: Mechanical vibrations.
- ISO 4406: Code to indicate the degree of purity.
- DIN 3967: Gearbox tolerances.
