Transmission Seal Compatibility and Preventive Replacement on the Lull 844C

[MikePhua]

Lull Telehandler History and the 844C Series
Lull telehandlers, originally developed by Lull Engineering Company in Minnesota, became widely known for their unique sliding boom design, which allowed operators to place loads with precision without repositioning the machine. The 844C model, part of the 8000 lb class, was designed for rugged construction environments and featured a Cummins 4BT diesel engine paired with a powershift transmission. These machines were commonly used in framing, masonry, and utility work across North America.
After several corporate transitions, including acquisition by JLG Industries, the Lull brand was eventually retired, but the 844C remains in active service due to its mechanical simplicity and robust frame. Thousands of units were sold throughout the 1990s and early 2000s, and many are still maintained by independent contractors and municipal fleets.
Terminology Annotation

• Front Transmission Seal: A radial lip seal located at the input shaft of the transmission, preventing fluid leakage between the engine and transmission interface.
  
• Directional Seal: A seal with molded grooves or arrows designed to channel fluid away from the sealing lip, enhancing leak resistance under rotation.
  
• Cross-Reference Seal: A replacement part matched by dimensions and material but not necessarily by design features such as directional ribs.
  

Why Replace the Seal During Engine Swap
When performing an engine swap—such as replacing or reinstalling a Cummins 4BT—it is common practice to inspect and replace the front transmission seal. Even if the original seal is not leaking, preventive replacement can avoid future downtime and fluid loss. The seal is accessible during engine removal, making it a low-cost insurance step.
In one documented case, a technician chose to replace the original directional seal with a cross-referenced part that lacked the molded arrows and ribs. This raised concerns about compatibility and long-term performance, especially under high rotational speeds and fluid pressure.
Differences Between Directional and Non-Directional Seals
Directional seals are engineered with helical ribs that actively pump fluid away from the sealing lip when the shaft rotates. This design is particularly effective in high-speed applications or where fluid splash is frequent. Non-directional seals rely solely on static sealing pressure and lip geometry.
Key differences:

• Directional seals reduce leak risk under dynamic conditions
  
• Non-directional seals may be sufficient for low-speed or intermittent use
  
• Material composition (e.g., nitrile vs. Viton) affects temperature and chemical resistance
  
• Shaft rotation direction must match the seal’s rib orientation for effectiveness
  

In the case of the Lull 844C, the transmission input shaft rotates consistently in one direction, making directional seals advantageous. However, if the replacement seal matches the dimensions and material but lacks ribs, it may still perform adequately in moderate-duty cycles.
Recommendations for Seal Selection and Installation
To ensure proper sealing and avoid premature failure:

• Match seal dimensions precisely: inner diameter, outer diameter, and width
  
• Confirm shaft rotation direction and select a seal with matching rib orientation if directional
  
• Use seals rated for transmission fluid and operating temperatures (typically -40°C to 120°C)
  
• Inspect the shaft surface for scoring or wear before installation
  
• Apply transmission-safe sealant sparingly around the outer diameter if recommended by the manufacturer
  
• Use a seal driver to install evenly without distortion
  

If unsure about compatibility, consult the transmission manufacturer or a seal supplier with access to OEM specifications. Some vendors offer upgraded seals with dual lips or spring-loaded designs for enhanced performance.
Field Anecdotes and Practical Advice
In Pennsylvania, a contractor performing a 4BT swap on a Lull 844C noted that the original seal had directional ribs and a part number that cross-referenced to a plain seal. After installing the new seal, he monitored for leaks over 200 hours of operation and found no issues. However, he later sourced a directional seal from a transmission rebuilder and replaced it during routine service for peace of mind.
In Texas, a fleet technician emphasized the importance of checking seal orientation markings. He once installed a directional seal backward, causing immediate leakage. Since then, he marks the shaft rotation direction on the housing during disassembly to avoid confusion.
Preventive Maintenance and Long-Term Reliability
To extend transmission life and reduce seal-related failures:

• Replace front transmission seals during any engine removal or clutch service
  
• Monitor fluid levels and inspect for seepage at the bellhousing
  
• Use high-quality transmission fluid with anti-foaming additives
  
• Avoid overfilling, which can increase internal pressure and stress seals
  
• Document seal part numbers and installation dates for future reference
  

Conclusion
Replacing the front transmission seal on a Lull 844C during an engine swap is a smart preventive measure. While directional seals offer enhanced leak resistance, non-directional replacements may suffice if properly matched and installed. Understanding seal geometry, shaft rotation, and material compatibility ensures long-term reliability and protects against costly fluid loss. With careful selection and attention to detail, operators can maintain the integrity of their telehandler’s drivetrain and keep it working efficiently for years to come.