Causes of misalignment in gearboxes

A coupling transfers torque between those shafts, connecting the motor to a gearbox or a gearbox to the driven equipment. When alignment falls outside of the acceptable limits, the coupling applies additional forces to nearby components. Even a flexible coupling has its limits, making alignment an important part of drivetrain reliability. 

Types of gearbox misalignment 

Parallel misalignment, or offset misalignment, occurs when the shaft centerlines remain parallel but are displaced horizontally or vertically. 

Horizontal angle misalignment happens when the centerlines form an angle when viewed from above. Vertical angle misalignment is when they form an angle viewed from the side. 

Compound misalignment combines the offset and angular errors. A combination of horizontal angular and offset misalignment, for example, requires correcting both the sideways displacement and the angle. Measuring only one plane can end up leaving another problem unresolved. 

Common causes of misalignment 

Improper installation is a common culprit. Positioning equipment by eye, using damaged mounting surfaces, or skipping final measurements can leave shafts outside tolerance. 

Soft foot occurs when a machine foot doesn’t sit properly against its support. Tightening that foot, however, can distort the housing and change shaft position. Dirt, bent feet, and poorly fitted shims can also contribute to this. 

Foundation settling shifts the equipment after installation, and cracked grout can also allow the assembly to move under load. Loose fasteners let repeated movements occur, which will undo previous adjustments. Thermal expansion adds another challenge: equipment that’s aligned while cold can start to shift as motors, gearboxes, and supports heat up.  

How misalignment damages gearboxes 

What does shaft misalignment lead to? Additional bearing loads, coupling wear, vibration, heat, and premature component failure are all common consequences. Our guidance on shaft loads explains why bearing selection has to account for the application forces. 

Excessive shaft movement wears seal lips, which allows lubricant leakage or contamination. When loading deflects shafts or distorts bearing supports, internal gear contact can change and concentrate the stress. STOBER’s guide to selecting the best gearbox oil offers useful lubrication context. 

How to detect misalignment 

Add alignment checks to your preventive maintenance process. Look out for rising vibration, unusual noise, recurring seal leaks, and higher temperatures, and compare readings to commissioning baselines under similar speeds and loads. 

Laser shaft alignment systems directly measure angular errors and coupling offsets. Motion amplification relies on video processing to make small movements visible, helping teams investigate relative movement around couplings and supports. 

Document the conditions behind each reading; a vibration change recorded during a speed increase can have a different explanation from one recorded at a steady load. Also, record measurement locations so technicians can repeat the same checks.  

If alignment repeatedly drifts after correction, investigate the support structure and mounting arrangement before moving the machine again, as repeated adjustments without finding the source of movement can leave the underlying fault active and raise the risk of downtime. 

Vibration analysis for misalignment 

Accelerometers measure small vibrations at the bearing housings. Vibration analysis examines frequencies, amplitudes, and trends to help identify developing faults. 

Phase analysis compares vibration timing at different measurement points to help identify angular misalignment. However, imbalance and looseness can have overlapping symptoms. Review multiple measurements and operating conditions before you decide which correction you need. 

Thermography for misalignment 

Thermal imaging spots surface temperature patterns. Friction that’s associated with misalignment often creates hot spots near bearings or couplings. 

Hot areas warrant mechanical investigation, but temperature alone can’t prove misalignment. Compare similar equipment under similar loads, and check the lubrication, cooling, and bearing condition, too. 

Oil analysis for gearbox misalignment 

Oil analysis reveals wear particles and contamination connected to component distress. Rising metal levels might signal bearing or gear wear, but they don’t determine misalignment. 

Review laboratory trends along with the vibration and alignment results. Follow the gearbox manufacturer’s instructions for lubricant sampling. Do not open sealed, maintenance-free gearboxes for oil analysis unless the manufacturer specifically permits it. 

How to correct misalignment 

Before making adjustments, stop the equipment and follow all lockout procedures. Inspect the base, mounting surfaces, fasteners, and coupling, and correct soft foot first; otherwise, tightening bolts can distort the machine again. For foot-mounted equipment, use clean, suitable shims under mounting feet to correct the vertical position. Adjust the front and rear feet, as needed, to address angular error. 

Use jack screws for controlled horizontal movement. After each adjustment, remeasure both planes, and tighten fasteners to the specified torque and repeat measurements, since tightening can change alignment. Record the final results for future reference. 

Coupling alignment under operating conditions 

Precision alignment reduces unwanted forces on gearbox bearings. Rigid couplings generally demand tighter alignment; flexible couplings accommodate limited movement within specified ratings. 

Don’t take a flexible coupling’s maximum allowable misalignment as the installation target. Instead, set alignment targets using shaft speed, coupling requirements, and equipment manufacturer specifications. 

Account for the thermal growth under your actual operating conditions; manufacturer recommendations or measured movement can establish appropriate cold alignment offsets so shafts approach their intended positions after warming up. 

Preventing future gearbox misalignment 

Recheck alignment after any major maintenance, equipment movement, or foundation repairs. Establish the baseline vibration readings after commissioning and retain all alignment records, mounting details, and operating temperatures. 

STOBER precision gearboxes support reliable drivetrain performance when properly selected and installed. Consult STOBER engineers for application guidance on gearbox sizing, bearing options, shaft loads, or mounting requirements. Contact STOBER by clicking the link below, calling (888) 786-2371, or emailing sales@stober.com.