JD 310D Reverser Oil Line Leak Caused by Obsolete Fittings and Flare Nut Seizure

[MikePhua]

Quick answer
A persistent leak on the rear fitting of the reverser oil feed tube in a John Deere 310D backhoe is likely due to seized flare nuts and aged ferrel-style fittings. The original part (AT101368) is discontinued, and repair requires heat treatment, mechanical separation, or sourcing replacements from aftermarket hydraulic specialists.
John Deere 310D background and reverser system overview
The JD 310D was introduced in the early 1990s as part of Deere’s D-series backhoe loaders. It featured:

• A 4.239L naturally aspirated diesel engine
  
• Hydraulic reverser transmission with torque converter
  
• Wet clutch packs for directional control
  
• Converter feed tube supplying pressurized oil to the reverser unit
  

The reverser allows seamless forward-reverse transitions without clutching, ideal for trenching and loader work. Oil is supplied through a rigid steel tube with flare fittings at both ends, connecting the transmission case to the reverser housing.
Leak diagnosis and fitting behavior
After resealing the reverser and replacing the engine rear main seal, the operator discovered a leak at the rear fitting of the converter feed tube. Despite tightening the nut, oil continued to seep. Upon removal, the fittings refused to separate from the flare nuts, suggesting corrosion or mechanical seizure.
Key observations:

• The reverser ports are 3/8" female pipe thread
  
• The fittings resemble flare or ferrel-style connections
  
• No rubber seals or O-rings are present inside the fitting
  
• The part number AT101368 is discontinued by Deere
  

This configuration is typical of industrial hydraulic systems from the 1980s–90s, where steel-on-steel sealing was common. Over time, heat cycling and fluid exposure cause flare nuts to seize, especially if dissimilar metals are used.
Repair strategy and mechanical separation
To separate the seized fittings:

• Apply penetrating oil and allow several hours to soak
  
• Use heat: A propane torch can expand the outer fitting and break corrosion bonds
  
• Strike the fitting lightly: A hammer tap can shock the threads loose
  
• Avoid over-tightening: Excess torque may split the ferrel or distort the flare
  

If the ferrel is cracked or the flare cone is damaged, the fitting will never seal properly. In such cases, replacement is the only option.
Replacement options and sourcing advice
Since AT101368 is discontinued, alternatives include:

• Joseph Industries: Specializes in legacy hydraulic components for construction equipment
  
• Hydraulic rebuild shops: Can fabricate custom tubes with matched flare angles
  
• Industrial supply vendors: May stock compatible 3/8" flare fittings and tubing
  

When sourcing replacements:

• Match thread type (NPT vs. SAE)
  
• Confirm flare angle (typically 37° for JIC or 45° for SAE)
  
• Use high-pressure rated tubing (minimum 3,000 PSI)
  
• Request zinc-coated or stainless steel to resist future corrosion
  

One technician rebuilt a similar line using Parker 37° flare fittings and a custom-bent steel tube, restoring full seal integrity.
Preventive measures and long-term reliability

• Use anti-seize compound on flare threads during reassembly
  
• Inspect fittings annually for signs of weeping or corrosion
  
• Replace aged tubing during major transmission service
  
• Label and photograph connections before disassembly to avoid routing errors
  

In cold climates, thermal contraction can exacerbate flare nut seizure. Preheating fittings before removal reduces risk of thread damage.
Conclusion
The JD 310D’s reverser oil line leak stems from seized flare fittings and obsolete part availability. With careful heat treatment and mechanical separation, the fittings may be salvaged. If not, aftermarket hydraulic suppliers can fabricate replacements. Understanding the fitting type and thread geometry is essential for restoring seal integrity and preventing future leaks.