08-27-2025, 08:00 PM
The Lull Legacy in Material Handling
Lull telehandlers, once a staple in North American construction, were known for their unique horizontal boom traversal system. Originally developed by Lull Engineering in the mid-20th century and later acquired by JLG Industries, these machines offered precise load placement and extended reach without repositioning the chassis. The Lull 644 and 944 series were particularly popular among framing crews and masonry contractors due to their ability to “reach and place” materials with minimal effort.
Though Lull-branded machines ceased production after JLG consolidated its telehandler lineup, thousands remain in active service. Their mechanical simplicity and robust hydraulic systems make them ideal for long-term use, provided maintenance is kept up—especially in the hydraulic circuit.
Understanding Hydraulic Cylinder Drift
Hydraulic cylinder drift refers to the unintended movement of a cylinder when the control lever is in the neutral position. In telehandlers, this often manifests as the boom slowly lowering or extending without operator input. Drift is typically caused by internal leakage past piston seals or failure in the control or counterbalance valves.
In Lull machines, drift affecting both the main boom lift and telescoping functions simultaneously suggests a shared hydraulic control issue rather than isolated cylinder wear. When multiple cylinders exhibit drift at the same time, the root cause is often upstream in the valve bank or joystick assembly.
Counterbalance Valves and Their Role
Counterbalance valves are designed to hold a load in position when the control valve is in neutral. They prevent gravity or external forces from moving the cylinder unless hydraulic pressure is intentionally applied. These valves are especially critical in boom lift and extension circuits, where loads are suspended and safety is paramount.
Each cylinder typically has its own counterbalance valve mounted either directly on the cylinder or on a nearby manifold. If the valve’s internal seals degrade or the spring setting shifts, the valve may allow fluid to bypass, resulting in drift.
In one case, a contractor noticed that both the boom lift and extension cylinders were drifting simultaneously. After inspecting the joystick and control valve, he discovered that the counterbalance valves shared a common joystick input. This led him to rebuild both valves using OEM o-ring kits, which contained over a dozen seals each. The repair significantly reduced drift in the boom lift, though the extension cylinder continued to drop overnight.
Hidden Valves and Overlooked Components
Some Lull models feature secondary counterbalance valves mounted on the opposite end of the cylinder or tucked into rear manifolds. These smaller valves are easy to miss during inspection, especially if the parts diagram shows them in a different location than the actual machine. In the case above, the operator later discovered a second valve on the extension boom manifold and rebuilt it as well, reducing overnight drift to less than an inch.
This highlights the importance of thorough inspection and cross-referencing diagrams with physical components. Hydraulic systems often evolve during production runs, and field modifications may alter valve placement.
Repair Strategies and Cost Considerations
Rebuilding counterbalance valves is a cost-effective solution compared to full cylinder replacement. OEM seal kits typically cost under $100, and local hydraulic shops can perform the rebuild for modest labor fees. In the documented case, the second valve was rebuilt for $58, bringing the total repair cost under $200.
Recommended steps include:
Preventive Maintenance and Long-Term Reliability
To minimize future drift and hydraulic issues:
Conclusion
Hydraulic cylinder drift in Lull telehandlers is often a symptom of valve seal degradation rather than cylinder failure. By understanding the role of counterbalance valves and inspecting all related components, operators can restore stability and safety without major expense. These machines, though no longer in production, continue to serve reliably thanks to their mechanical transparency and field-repairable design. With proper care, a Lull can remain a trusted lifting partner for decades.
Lull telehandlers, once a staple in North American construction, were known for their unique horizontal boom traversal system. Originally developed by Lull Engineering in the mid-20th century and later acquired by JLG Industries, these machines offered precise load placement and extended reach without repositioning the chassis. The Lull 644 and 944 series were particularly popular among framing crews and masonry contractors due to their ability to “reach and place” materials with minimal effort.
Though Lull-branded machines ceased production after JLG consolidated its telehandler lineup, thousands remain in active service. Their mechanical simplicity and robust hydraulic systems make them ideal for long-term use, provided maintenance is kept up—especially in the hydraulic circuit.
Understanding Hydraulic Cylinder Drift
Hydraulic cylinder drift refers to the unintended movement of a cylinder when the control lever is in the neutral position. In telehandlers, this often manifests as the boom slowly lowering or extending without operator input. Drift is typically caused by internal leakage past piston seals or failure in the control or counterbalance valves.
In Lull machines, drift affecting both the main boom lift and telescoping functions simultaneously suggests a shared hydraulic control issue rather than isolated cylinder wear. When multiple cylinders exhibit drift at the same time, the root cause is often upstream in the valve bank or joystick assembly.
Counterbalance Valves and Their Role
Counterbalance valves are designed to hold a load in position when the control valve is in neutral. They prevent gravity or external forces from moving the cylinder unless hydraulic pressure is intentionally applied. These valves are especially critical in boom lift and extension circuits, where loads are suspended and safety is paramount.
Each cylinder typically has its own counterbalance valve mounted either directly on the cylinder or on a nearby manifold. If the valve’s internal seals degrade or the spring setting shifts, the valve may allow fluid to bypass, resulting in drift.
In one case, a contractor noticed that both the boom lift and extension cylinders were drifting simultaneously. After inspecting the joystick and control valve, he discovered that the counterbalance valves shared a common joystick input. This led him to rebuild both valves using OEM o-ring kits, which contained over a dozen seals each. The repair significantly reduced drift in the boom lift, though the extension cylinder continued to drop overnight.
Hidden Valves and Overlooked Components
Some Lull models feature secondary counterbalance valves mounted on the opposite end of the cylinder or tucked into rear manifolds. These smaller valves are easy to miss during inspection, especially if the parts diagram shows them in a different location than the actual machine. In the case above, the operator later discovered a second valve on the extension boom manifold and rebuilt it as well, reducing overnight drift to less than an inch.
This highlights the importance of thorough inspection and cross-referencing diagrams with physical components. Hydraulic systems often evolve during production runs, and field modifications may alter valve placement.
Repair Strategies and Cost Considerations
Rebuilding counterbalance valves is a cost-effective solution compared to full cylinder replacement. OEM seal kits typically cost under $100, and local hydraulic shops can perform the rebuild for modest labor fees. In the documented case, the second valve was rebuilt for $58, bringing the total repair cost under $200.
Recommended steps include:
- Identify all counterbalance valves associated with drifting cylinders
- Source OEM or high-quality aftermarket seal kits
- Remove valves carefully, noting orientation and hose routing
- Clean all internal surfaces and replace seals
- Reinstall and test under load, monitoring for drift over 24 hours
Preventive Maintenance and Long-Term Reliability
To minimize future drift and hydraulic issues:
- Replace hydraulic fluid every 1,000 hours or annually
- Inspect valve seals and cylinder rods for wear or scoring
- Keep breather caps and reservoir filters clean to prevent contamination
- Exercise all hydraulic functions regularly to prevent seal hardening
- Use manufacturer-recommended fluid viscosity for seasonal conditions
Conclusion
Hydraulic cylinder drift in Lull telehandlers is often a symptom of valve seal degradation rather than cylinder failure. By understanding the role of counterbalance valves and inspecting all related components, operators can restore stability and safety without major expense. These machines, though no longer in production, continue to serve reliably thanks to their mechanical transparency and field-repairable design. With proper care, a Lull can remain a trusted lifting partner for decades.
