Gear Pump Seal Replacement and Hydraulic Reliability in the Lull 844B Telehandler

[MikePhua]

The Lull 844B and Its Role in Material Handling
The Lull 844B is a rough-terrain telehandler designed for lifting and placing materials in construction, agriculture, and industrial settings. Manufactured under the Lull brand—later acquired by JLG—the 844B features a unique horizontal boom pivot system that allows precise load placement without repositioning the chassis. With a lift capacity of 8,000 pounds and a maximum reach of 44 feet, the machine became a staple on job sites requiring reach and stability.
Lull’s design philosophy emphasized operator control and mechanical simplicity. The 844B was powered by a diesel engine driving a hydraulic system that controlled boom extension, tilt, and auxiliary functions. At the heart of this system was a gear-type hydraulic pump, responsible for generating flow and pressure to actuate cylinders and motors.
Understanding Gear Pump Function and Seal Design
Gear pumps operate by trapping fluid between rotating gears and the pump housing, then forcing it through the outlet port under pressure. The Lull 844B typically uses a fixed-displacement gear pump mounted directly to the engine or transmission housing. These pumps are known for their durability and simplicity but rely heavily on internal and external seals to maintain pressure and prevent leakage.
Key sealing components include:

• Shaft seal: Prevents hydraulic fluid from leaking around the drive shaft
  
• Body-to-cover gasket: Seals the mating surfaces of the pump housing
  
• O-rings or lip seals around inlet and outlet ports
  
• Backup rings to prevent extrusion under high pressure
  
• Wear plates and bushings that maintain internal tolerances
  

Terminology Note: “Fixed-displacement” means the pump delivers a constant volume per revolution. “Shaft seal” is a radial seal around the rotating shaft, often made of nitrile or Viton rubber.
In 2023, a contractor in Arizona noticed hydraulic fluid pooling beneath his 844B after cold starts. Inspection revealed a cracked shaft seal that had hardened over time. After replacing the seal and flushing the system, the leak stopped and pressure returned to spec.
Symptoms of Seal Failure and Diagnostic Strategy
Seal failure in gear pumps can manifest in several ways:

• External fluid leaks at the pump flange or shaft
  
• Loss of hydraulic pressure or slow cylinder response
  
• Air intrusion causing foamy fluid or erratic movement
  
• Increased pump noise due to cavitation or wear
  
• Contaminated fluid from degraded seal material
  

Diagnostic steps:

• Clean pump exterior and monitor for fresh leaks
  
• Use pressure gauge to test output at control valve
  
• Inspect fluid for air bubbles or discoloration
  
• Remove pump and check shaft seal for cracks or hardening
  
• Measure housing flatness and gear wear for internal leakage
  

A technician in Maine diagnosed a pressure drop in a Lull 844B and traced it to a worn body gasket that allowed internal bypass. After replacing the gasket and torqueing the cover bolts evenly, the pump regained full output.
Seal Replacement Procedure and Best Practices
Replacing gear pump seals requires precision and cleanliness. General steps include:

• Disconnect hydraulic lines and drain fluid
  
• Remove pump from engine or transmission mount
  
• Disassemble pump housing using proper tools
  
• Extract old seals with seal puller or pick
  
• Clean all surfaces with lint-free cloth and solvent
  
• Install new seals using seal driver or press
  
• Reassemble pump and torque bolts to spec
  
• Refill system and bleed air from lines
  

Recommendations:

• Use OEM or high-quality aftermarket seal kits
  
• Match seal material to fluid type and temperature range
  
• Replace all seals during service, not just the failed one
  
• Inspect shaft for scoring and polish if needed
  
• Test pump on bench before reinstalling
  

In 2022, a fleet manager in Texas rebuilt three gear pumps from Lull 844B units using Viton seals rated for high-temperature synthetic fluid. The upgrade extended seal life and reduced downtime during summer operations.
Preventive Maintenance and System Longevity
To extend gear pump and seal life:

• Change hydraulic fluid every 1,000 hours or annually
  
• Use filters with 10-micron rating or better
  
• Monitor fluid temperature and avoid overheating
  
• Inspect pump mounting bolts for vibration loosening
  
• Keep spare seal kits and gaskets in inventory
  

Upgrade options:

• Install fluid temperature sensor with cab alert
  
• Use magnetic drain plugs to detect wear particles
  
• Retrofit pump with external case drain to reduce seal pressure
  
• Add inline pressure gauge for real-time monitoring
  

A technician in British Columbia added case drains to all gear pumps in his telehandler fleet. The modification reduced shaft seal failures by relieving internal pressure spikes during cold starts.
Conclusion
Gear pump seal failure in the Lull 844B telehandler can lead to hydraulic inefficiency, fluid loss, and operational downtime. With proper diagnostics, high-quality replacement seals, and preventive upgrades, the pump can be restored to full performance and reliability. In material handling, hydraulic pressure is the lifeblood—and the seals are its guardians. Keeping them intact means keeping the lift moving, the boom reaching, and the job on schedule.