TL;DR

Vibration is most often a worn bearing. Listen for grinding, log a vibration reading, and plan a bearing replacement during the next planned outage.

What you might see

rumbling or grinding noise
elevated vibration at running speed
warm motor housing
shaft whip or knock

Likely causes

Tap to mark as ruled out

Worn or pitted bearings, typical after 30,000+ operating hours
Bearing contamination from dirt, moisture, or grease degradation
Bearing electrical fluting from VFD common-mode currents (no shaft grounding ring)
Coupling misalignment driving load into the motor bearings

Required tools

IR thermometer
Vibration meter (optional but recommended)
LOTO kit
Replacement bearings per Baldor nameplate

Safety first

Lock out and tag out the motor disconnect before opening the conduit box or rotating the shaft by hand on a coupled load.
Never reach into a coupling unless the disconnect is locked out and you have verified zero rotation.

Procedure

7 steps · ~30 min

1
Stop the motor and lock out / tag out the upstream disconnect.
2
Rotate the shaft by hand and listen for grinding, catching, or roughness in the bearing.[1]
3
Measure the motor housing temperature near each bearing with an IR thermometer; readings above 85°C trend toward failure.
4
If you have a vibration meter, take a reading at the drive-end and non-drive-end bearing housings. Velocity above 0.4 in/s is a red flag.
5
Check the maintenance log for total operating hours. If the motor has more than 30,000 hours and you have any bearing symptom, plan a bearing change at the next outage.[1]
6
Order replacement bearings by the part number on the Baldor nameplate. Match shielding and grease grade exactly.
7
If vibration is severe (>0.4 in/s) or the motor is making intermittent grinding, schedule the replacement immediately rather than waiting.

Sources

Baldor Reliance Industrial Motor Maintenance Manual, Baldor Electric Company (ABB)
Baldor Industrial Motor Maintenance Manual, bearing inspection and replacement procedures (general)
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