Why Does the Grove RT-60S Cab Growl When Rotating Under Load

[MikePhua]

The Grove RT-60S and Its Role in Mid-Range Lifting
The Grove RT-60S is a rough terrain crane designed for industrial lifting, plant maintenance, and construction logistics. Manufactured by Grove, a company founded in 1947 and later acquired by Manitowoc in 2002, the RT-60S was part of Grove’s push to offer compact, mobile cranes with high lifting capacity and off-road capability. With a rated capacity of 60 tons and a boom length exceeding 100 feet, the RT-60S became a popular choice for machinery movers and rental fleets.
Its hydraulic swing system allows the superstructure to rotate smoothly under load, but like many mid-size cranes, it relies heavily on proper lubrication, bearing integrity, and operator technique to maintain performance. When the cab begins to “growl” or vibrate during rotation under load, it’s often a sign of mechanical stress or insufficient maintenance.
Identifying the Source of the Growl
Operators have described a low-frequency vibration or audible growl when rotating the superstructure with a heavy load. This sensation is typically felt through the seat and control levers and may be accompanied by slight shaking. The most common causes include:

• Insufficient lubrication in the swing bearing
  
• Excessive wear or runout in the turntable bearing
  
• Hydraulic pressure fluctuations during swing
  
• Structural flexing under near-capacity loads
  

Terminology clarification:

• Swing Bearing: A large-diameter bearing that allows the crane’s upper structure to rotate on the lower frame
  
• Turntable Runout: The amount of vertical movement or wobble in the bearing under load
  
• Grease Zerk: A fitting used to inject lubricant into bearings or joints
  

In one case, the operator was lifting a large industrial oven and noticed the growl during rotation. The load was significant, though not at full chart capacity, suggesting that the issue was mechanical rather than operational.
Measuring Swing Bearing Deflection
To assess the condition of the swing bearing, technicians recommend measuring vertical deflection under load. This involves:

• Blocking the boom and applying downward pressure
  
• Measuring the distance between the frame and the top of the swing bearing
  
• Performing a lift near rated capacity and re-measuring
  

Acceptable deflection is typically under 0.5 inches, though exact specifications vary by model. A dial indicator can be used to measure runout by rocking the boom back and forth at different angles. If the bearing shows excessive movement or the cab rocks noticeably, it may be time for replacement.
Greasing the Swing Bearing Properly
One of the most overlooked maintenance tasks is swing bearing lubrication. The RT-60S typically has two grease fittings mounted to a plate, with lines running to the bearing. To ensure proper lubrication:

• Use high-quality grease rated for heavy-duty bearings
  
• Inject ¾ to 1 full tube of grease while rotating the superstructure
  
• Avoid low-grade or contaminated grease, which can accelerate wear
  

A technician in Indiana noted that many Grove cranes respond well to fresh grease, especially if the bearing hasn’t been serviced recently. He recommended greasing while the crane is actively swinging to distribute lubricant evenly.
Estimating Load Without a Scale
For operators working without a load cell or scale, estimating weight becomes critical to avoid structural overload. One method involves using the winch as a crude scale:

• Determine the winch’s line pull capacity (e.g., 6,000–7,000 lbs per part of line)
  
• Use known weights (like a forklift or trailer) to calibrate
  
• Monitor engine RPM and winch strain during lifts
  

For example, if a crane is rated for 20,000 lbs at a given radius, using four parts of line allows roughly 5,000 lbs per part. If the winch begins to strain before the load lifts, the operator knows they’re near or over chart limits.
Safe Operating Practices and Radius Management
When lifting unknown weights, especially in machinery moving or scrapping operations, it’s safer to boom in after lifting rather than boom out with a suspended load. This reduces radius and increases stability. Operators should:

• Test lift near the ground before booming out
  
• Use outrigger pads on soft ground to distribute load
  
• Avoid swinging heavy loads over the side unless chart permits
  

One operator shared his practice of lifting loads directly over the side—typically the weakest point in the chart—to verify safety before setting them over the front. He also emphasized the value of large outrigger pads, especially on lawns or soft soil, where smaller pads may sink or shift.
When Growling Is Normal and When It’s Not
Some Grove cranes naturally emit a growl under heavy load, especially when rotating at low RPM or near chart limits. However, persistent vibration, excessive rocking, or audible grinding may indicate bearing wear or hydraulic imbalance.
A rental fleet manager recalled a Grove unit that growled consistently but measured within factory specs. The machine operated safely for years, though operators were trained to throttle up during rotation and avoid abrupt movements.
Conclusion
A growling cab on the Grove RT-60S during rotation under load is often a sign of mechanical stress, lubrication deficiency, or nearing structural limits. By measuring bearing deflection, greasing properly, and estimating load with practical methods, operators can maintain safe and efficient lifting operations.
The RT-60S remains a trusted tool in the field, but like any crane, it speaks to its operator—sometimes with a growl. Listening carefully, maintaining diligently, and lifting wisely ensures that the message is one of performance, not warning.