Troubleshooting / Gearbox

Gearbox Troubleshooting

The most common gearbox problems on the plant floor, with the likely causes and the fix for each. Part of the OEE Lab troubleshooting directory.

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Problems on this page:

OverheatingNoise or whineOil leakGear tooth wear or pittingWater or dirt in the oilBearing failure inside the gearboxBacklash increasingVibration rising

Overheating

Hits OEE: Availability

Symptoms: High case temperature, thinning oil, discolouration.

Overfilled or low oil
Set oil to the correct level; both extremes cause heat.
Wrong lubricant
Use the specified grade/viscosity.
Overload
Confirm load within rating; check service factor.
Blocked cooling/breather
Clean cooling surfaces; clear the breather.

Prevention: Oil level/analysis, correct lubricant, load and breather checks.

Noise or whine

Hits OEE: Quality

Symptoms: Whine, growl or knocking that changes with speed/load.

Worn/pitted gears
Inspect gear teeth; replace worn gearsets.
Bearing wear
Identify and replace failing bearings.
Backlash/misalignment
Check and reset backlash; align input/output.
Low/contaminated oil
Top up or change oil; investigate contamination source.

Prevention: Oil analysis, vibration checks, alignment, contamination control.

Oil leak

Hits OEE: Availability

Symptoms: Oil around the seals or joints, falling oil level, a slip hazard and a contamination risk.

Worn shaft seals
Replace the input and output seals and check the shaft surface where the seal runs.
Blocked breather (pressure build-up)
Clean or replace the breather so pressure cannot build inside the case.
Overfilled or wrong oil
Drain to the correct level and use the grade on the nameplate.
Gasket or cover joint failed
Re-seal the joint and tighten the cover bolts evenly.

Prevention: Seal and breather checks on the route, correct oil level and grade.

Gear tooth wear or pitting

Hits OEE: Availability

Symptoms: Pitting, scuffing or polished tooth faces seen at inspection, and noise rising over weeks.

Oil too thin or the wrong grade for the load
Use the oil grade on the nameplate or in the manual.
Overload or shock loads
Check the actual load against the gearbox rating and service factor.
Contaminated oil
Change the oil and find how dirt or water got in.
Misalignment with the motor or driven machine
Re-align the input and output couplings.

Prevention: Tooth inspections through the inspection cover at planned shutdowns, and oil analysis.

Water or dirt in the oil

Hits OEE: Availability

Symptoms: Milky or dark oil, sludge on the dipstick, particles on the drain plug magnet.

Breather letting in moisture or dust
Fit a desiccant or filtered breather suited to the area.
Washdown water getting past the seals
Keep direct spray off the seals and use seals rated for washdown.
Oil change intervals stretched
Change the oil at the maker's interval or on oil analysis.
Dirty top-up containers
Use clean, labelled containers for top-ups.

Prevention: Oil analysis on critical gearboxes and clean oil handling.

Bearing failure inside the gearbox

Hits OEE: Availability

Symptoms: Rising noise and heat at one shaft, play in the shaft, metal particles in the oil.

Oil level wrong for the mounting position
Check the fill level for the actual mounting position, which can differ from the standard one.
Overhung load too high (belt or chain too tight)
Check belt or chain tension and the overhung load rating.
Contaminated oil
Change and flush the oil and fix the source of contamination.
Bearing damaged at fitting
Use the correct fitting tools and procedure at overhaul.

Prevention: Vibration trending on the bearing positions and correct belt tension.

Backlash increasing

Hits OEE: Quality

Symptoms: Play at the output shaft, positioning errors, a knock when the drive reverses.

Gear wear
Measure backlash, compare it with the manual and plan a rebuild.
Worn keys, keyways or loose coupling hubs
Check keys and hubs for fretting and looseness.
Bearing wear allowing the shaft to move
Replace the worn bearings.
Loose mounting bolts
Re-tighten the gearbox mounting to the specified torque.

Prevention: Backlash measured at planned intervals on positioning drives.

Vibration rising

Hits OEE: Availability

Symptoms: Vibration readings climb on the trend and the base or guard rattles.

Misalignment
Re-align the couplings after any work.
Soft foot or loose base bolts
Check the feet and tighten the base.
Gear or bearing damage
Use vibration analysis to tell gear mesh problems from bearing problems.
Unbalanced coupling or driven load
Check the coupling and the driven machine.

Prevention: Vibration readings on a route with trend alarms.

Guidance only. Always follow lockout/tagout and your site's safe-work procedures, and verify against OEM manuals before acting.

Related equipment guides: coupling · bearing · fan blower · electric motor · meat grinder · roll forming machine · wire drawing machine · electric chain hoist · gear hobbing machine · pulper · internal mixer · two roll mill

Stop the same fault coming back

Recurring gearbox stops usually trace to a cause you cannot see by hand. The partner we recommend is Fabrico: it tracks OEE and downtime live from PLCs, IoT sensors or AI cameras; where cameras are fitted, the video of a stop sits next to its machine data so the cause can be reviewed; and a technician opens the work order from the stop in the same system. Data is hosted in the AWS EU region, and Fabrico and the company behind it hold ISO/IEC 27001, ISO/IEC 20000-1 and ISO 9001.

Book a Fabrico demo
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Related tools: full troubleshooting directory · OEE calculator · downtime cost · MTBF / MTTR · glossary

Methods that cut recurring stops: the six big losses · root cause analysis · preventive vs predictive maintenance · TPM · SMED & changeover