Restoring the Air Intake and Exhaust System on an International 3400A

[MikePhua]

The International 3400A tractor-loader-backhoe, a rugged utility machine from the 1970s and early 1980s, often requires custom solutions when original air intake and muffler components are missing or deteriorated. Owners restoring these machines for farm or light construction use must navigate parts scarcity, fabrication options, and performance considerations.
International Harvester’s 3400A Legacy
The 3400A was part of International Harvester’s industrial tractor line, designed for municipal, agricultural, and utility work. Built on a heavy-duty chassis with a front loader and optional backhoe, it featured a naturally aspirated diesel engine, mechanical transmission, and open hydraulic system. IH, founded in 1902, was a major player in agricultural and industrial equipment until its merger into Case IH in the mid-1980s.
While exact production numbers are hard to trace, the 3400A was widely distributed across North America. Many units remain in service today, especially on retirement farms and small rural properties.
Terminology Notes

• Under-Hood Muffler: A compact exhaust silencer mounted within the engine bay, designed to reduce noise and direct fumes away from the operator.
  
• Air Intake Stack: A vertical pipe or duct that draws air from above the hood or cab, reducing dust ingestion and improving filter life.
  
• Tan Watery Hydraulic Fluid: A sign of water contamination in the hydraulic system, often due to condensation or poor sealing.
  
• Galvanized Pipe Retrofit: A non-standard replacement using plumbing pipe instead of OEM rubber hoses, common in field repairs.
  

Muffler Replacement Options
The original under-hood muffler may be difficult to source. Options include:

• OEM Reproduction Mufflers: Available from vintage parts suppliers or salvage yards. Match flange size and outlet direction.
  
• Universal Tractor Mufflers: Brands like Stanley or Donaldson offer bolt-on units with similar dimensions.
  
• Custom Fabricated Pipe: While tempting, deleting the muffler entirely can increase exhaust noise, raise backpressure, and affect engine performance. A straight pipe may also violate local noise ordinances.
  

If fabricating a replacement, ensure:

• Pipe diameter matches engine outlet
  
• Heat shielding is installed to protect nearby components
  
• Exhaust routing avoids cab and intake areas
  

Air Intake Restoration
The black plastic intake stack that extends over the radiator is critical for clean airflow. If missing:

• Use a Vertical Stack with Pre-Cleaner: Cyclonic pre-cleaners reduce dust and extend filter life.
  
• Fabricate a Duct Using ABS or PVC: Ensure it’s UV-resistant and securely mounted.
  
• Install a New Filter Housing: Match filter size and flow rating to engine specs.
  

Avoid drawing air from under the hood, where heat and dust reduce efficiency.
Hydraulic System Cleanup
During restoration, the owner discovered:

• Trash in the top strainer of the hydraulic filter
  
• Tan, watery fluid indicating contamination
  
• Aluminum-like sludge in the bell housing
  

Recommendations:

• Flush the Hydraulic System Thoroughly: Use low-viscosity flushing fluid and cycle all functions.
  
• Replace All Filters: Include suction, return, and pilot filters.
  
• Inspect Galvanized Pipe Sections: Replace with proper hydraulic hose to prevent electrochemical corrosion and flow restriction.
  

Field Anecdotes and Practical Insight
In North Carolina, a retired technician restoring a 3400A found that the power steering was disabled due to a push-pull hydraulic valve on the fender. After cleaning the system and replacing filters, steering returned to normal. He fabricated a new intake stack using black ABS pipe and installed a Donaldson pre-cleaner to reduce filter changes.
In Oregon, a farmer replaced the muffler with a straight pipe but later added a silencer after neighbors complained about the noise during early morning starts.
Recommendations for Restoration

• Document All Hose and Pipe Sizes: Helps when sourcing replacements or fabricating new sections.
  
• Use OEM Specs When Possible: Avoid improvisation that compromises safety or performance.
  
• Install Heat Shields Around Exhaust Components: Protect wiring and intake ducts.
  
• Test Hydraulic Functions After Fluid Change: Look for sluggish response or cavitation.
  

Final Thoughts
Restoring the air intake and exhaust system on an International 3400A requires a mix of historical knowledge, fabrication skill, and practical judgment. With careful planning and attention to airflow, noise, and fluid integrity, these machines can be returned to reliable service—ready to dig, lift, and haul for decades to come.