Nothing worries operators more than unexpected sounds from running equipment. Unusual noise from a gearbox doesn’t always mean it’s broken — but it’s always a signal that something isn’t right. Today, let’s talk about how we diagnose gearbox condition based on sound and vibration.
First, learn to “read” the noise
A gearbox sounds completely different under different conditions. Our test stand technicians have developed these rules of thumb over years of experience:
- Continuous “humming” sound
If the noise is low-pitched and persistent, accompanied by noticeable vibration on the housing, it’s usually a sign of bearing wear. As bearing clearance increases, rolling elements no longer run smoothly within the raceway, producing this type of background noise.
- Rhythmic “clicking” or “knocking” sound
This noise occurs at the same frequency as the rotational speed — a click or knock at a fixed interval per revolution. It most likely indicates severe pitting, spalling, or even a broken tooth on the gear face. In this case, shut down immediately for inspection. Continuing to run will cause further damage to additional gears.
- High-pitched “whining” or “screaming” sound
High-frequency whining is often related to gear meshing. Possible causes include: poor gear surface finish, oil film breakdown due to inadequate lubrication, or improper gear mesh clearance during assembly.
How do we assess vibration?
Sound is for the ears; vibration is for the hands and instruments.
· Hand-feel vibration: Place your palm on the housing. Under normal operation, vibration should feel smooth and fine. If you feel a rhythmic “jerking” or “stuttering,” it indicates binding somewhere in the driveline — commonly caused by coupling misalignment or loose foundation bolts.
· Radial runout: Use a dial gauge to measure the radial runout of the output shaft. If the reading exceeds the specified tolerance, the issue points to bearing wear or a bent output shaft.
How does Kunka test on the test stand?
Every Kunka gearbox undergoes a 4- to 6-hour test run before leaving the factory. During this process, our technicians use a sounding rod to listen to bearing housings and gear mesh zones section by section, while measuring vibration amplitudes at multiple points on the housing with a vibration meter. Data is recorded both during cold start and at thermally stable operation. Any abnormal fluctuations are flagged and re-inspected until the root cause is identified.
A final recommendation
If you hear unusual noise on-site, first identify the type of sound, then decide whether it’s safe to continue running. If you’re unsure, record a short audio clip and send it to Kunka Tech — our engineers will help you listen and diagnose.[Contact Us→]