JLG 400S Swing Bearing Grease Points and Turntable Lubrication Strategy

[MikePhua]

The 400S and JLG’s Boom Lift Engineering
The JLG 400S telescopic boom lift was introduced as part of JLG’s mid-range aerial work platform lineup, designed for construction, maintenance, and industrial access. With a platform height of 40 feet and a horizontal outreach of over 33 feet, the 400S combines reach, stability, and maneuverability. Its four-wheel drive and oscillating axle allow operation on uneven terrain, while the swing bearing and turntable assembly provide 360-degree rotation for precise positioning.
JLG Industries, founded in 1969, became a global leader in aerial access equipment by focusing on safety, serviceability, and hydraulic refinement. The swing bearing—also known as the slewing ring—is a critical component that supports the rotating upper structure and allows smooth, controlled movement. Proper lubrication of this bearing is essential for long-term reliability and load-bearing integrity.
Terminology Annotation:

• Swing Bearing (Slewing Ring): A large-diameter bearing that allows rotation of the boom and platform assembly relative to the chassis.
  
• Turntable: The rotating platform mounted atop the swing bearing, supporting the boom and operator controls.
  
• Oscillating Axle: A suspension feature that allows the axle to pivot, improving traction on uneven surfaces.
  

Locating and Identifying Grease Fittings
The swing bearing on the JLG 400S is equipped with multiple grease fittings—also called zerks—positioned around the circumference of the bearing race. These fittings allow grease to be injected into the bearing channels, ensuring even distribution across the ball or roller paths.
Typical configuration includes:

• 4 to 8 grease fittings spaced evenly around the bearing
  
• Fittings accessible through turntable cutouts or service panels
  
• Some units may have remote grease lines routed to a central manifold
  

Recommendations:

• Use a flashlight and mirror to inspect fitting locations during service
  
• Rotate the turntable slowly to expose hidden fittings
  
• Clean each fitting before greasing to prevent contamination
  
• Replace damaged or missing zerks with OEM-compatible units
  

In one maintenance shop in Alberta, a technician discovered that two fittings had been painted over during a refurbishment. After cleaning and replacing the zerks, grease flow was restored and bearing noise reduced.
Greasing Procedure and Lubricant Selection
Proper greasing of the swing bearing involves:

• Using a high-pressure grease gun with a flexible hose
  
• Applying lithium-based EP2 grease with anti-wear additives
  
• Injecting grease until fresh lubricant purges from the bearing seal
  
• Rotating the turntable during greasing to distribute lubricant evenly
  

Greasing frequency depends on usage:

• Every 250 hours for standard operation
  
• Every 100 hours in dusty or wet environments
  
• After pressure washing or exposure to corrosive materials
  

Terminology Annotation:

• EP2 Grease: Extreme pressure grease with NLGI Grade 2 consistency, suitable for high-load bearings.
  
• Purge Point: The location where old grease exits the bearing, indicating full lubrication.
  
• Flexible Hose: A grease gun accessory that allows access to tight or angled fittings.
  

In one industrial fleet in Georgia, switching to synthetic EP2 grease extended bearing life by 30% and reduced maintenance downtime.
Common Issues and Preventative Measures
Neglecting swing bearing lubrication can lead to:

• Bearing noise or grinding during rotation
  
• Uneven wear and reduced load capacity
  
• Seal failure and grease leakage
  
• Turntable binding or jerky movement
  

Preventative strategies:

• Maintain a greasing log with hours and fitting status
  
• Inspect seals quarterly for cracking or extrusion
  
• Avoid over-greasing, which can damage seals
  
• Train operators to report abnormal rotation sounds
  

In one construction site in Nevada, a 400S developed a rotational stutter. Inspection revealed dry bearing channels and hardened grease. After flushing and re-lubricating, the issue was resolved and rotation returned to normal.
Access Challenges and Service Tips
Accessing grease fittings can be difficult due to:

• Limited clearance between turntable and chassis
  
• Obstructed view from hoses or wiring
  
• Fittings located behind structural members
  

Solutions:

• Use low-profile grease couplers for tight spaces
  
• Install remote grease lines during overhaul
  
• Rotate the boom to optimal service position before greasing
  
• Use color-coded caps to mark serviced fittings
  

In one rental fleet in Texas, technicians added remote grease manifolds to all swing bearings, reducing service time by 40% and improving consistency.
Conclusion
Greasing the swing bearing on a JLG 400S is a critical maintenance task that protects the turntable’s rotational integrity and load-bearing performance. With proper identification of fittings, correct lubricant selection, and consistent service intervals, operators can ensure smooth operation and extend component life. In aerial lifts, rotation is precision—and grease is the silent force that keeps it turning.