Replacing an Aging TD6 with a Caterpillar D4H

[MikePhua]

The Legacy of the International TD6
The International Harvester TD6 was a post-war crawler tractor introduced in the late 1940s, powered by a two-cylinder gasoline starting engine coupled to a four-cylinder diesel main engine. It was a compact, reliable machine for its time, widely used in farming, logging, and light construction. Many TD6 units were purchased by small landowners who needed affordable mechanization. Its mechanical simplicity made it easy to repair, but by the 21st century, most surviving TD6s were showing their age—leaking seals, worn clutches, and obsolete parts.
In one case, a farmer who had inherited his father’s TD6—purchased in 1963 with a mortgage on the farm—was faced with the decision to either restore the aging machine or replace it with something more capable. The TD6 had sentimental value, but its limitations were becoming a liability.
Introducing the Caterpillar D4H
The Caterpillar D4H was introduced in the mid-1980s as part of Caterpillar’s H-series dozers, offering hydrostatic drive, improved operator comfort, and increased horsepower. The D4H filled the niche between the smaller D3 and the heavier D5, making it ideal for land clearing, grading, and agricultural work.
Caterpillar Inc., founded in 1925, had by then become the global leader in tracked equipment. The D4H was produced in several configurations, including XL (extra long), LGP (low ground pressure), and standard track. Its popularity extended across North America, Australia, and New Zealand, with thousands of units sold.
Key specifications include:

• Engine: Caterpillar 3204 or 3304 four-cylinder diesel
  
• Horsepower: 95–105 HP depending on model
  
• Operating weight: 10–11 metric tons
  
• Transmission: Hydrostatic drive
  
• Track gauge: Varies by configuration (standard, XL, LGP)
  

Engine Variants and Performance
The D4H came with either the 3204 or 3304 engine. The 3204 produced around 95 HP, while the 3304 delivered 105 HP. Both engines were known for their torque and reliability. Despite being four-cylinder units, they performed comparably to six-cylinder engines in similar-sized machines.
Terminology annotation:

• Hydrostatic drive: A transmission system using hydraulic fluid to transfer power, allowing smooth variable-speed control.
  
• LGP: Low Ground Pressure configuration with wider tracks for soft terrain.
  
• Blow-by: Combustion gases escaping past piston rings into the crankcase, often a sign of engine wear.
  

Operators noted that the D4H could push aggressively without bogging down, even in scrub or clay. One user reported putting over 5,000 hours on a D4H with minimal issues beyond hydraulic hose replacements.
Structural Weak Points and Inspection Tips
While the D4H is generally robust, there are known areas to inspect before purchase:

• Roller frame cracks near the track adjuster cover
  
• Pivot shaft flange wear where the roller frame attaches to the tractor
  
• Angle ram bushings on the C-frame, which can explode under stress if not greasable
  
• Final drive bearings, which are relatively easy and affordable to replace
  

A telltale sign of roller frame cracking is a string of grease leaking from the weld seam. Buyers should also check for excessive blow-by from the breather tube, which may indicate worn piston rings or valve guides.
Operational Considerations and Fuel Use
The D4H is efficient for its size but can consume fuel aggressively when operated at full throttle. In scrub-clearing applications, operators often work the governor hard, leading to higher fuel burn. However, the productivity gained offsets the cost in many cases.
One contractor in Australia outfitted his D4H with tree spears and a walkin-stick rake for clearing bushland. Despite the fuel usage, he found the machine ideal for the task, citing its maneuverability and pushing power.
Comparing Alternatives and Market Realities
In regions like New Zealand, small dozers are scarce. Alternatives such as Komatsu D31s or John Deere 650s are available but often priced higher. A 2000 JD 650H LGP with 4,800 hours and an enclosed cab was listed at NZD 70,000—well above the budget for many farmers.
The D4H, by contrast, was valued around NZD 30,000–35,000, making it a more accessible option. Auctions can drive prices higher, as seen when one unit reached NZD 61,000—beyond the bidder’s limit.
Test Drive and Evaluation Advice
Before committing to a purchase, prospective buyers should:

• Run the machine until fully warm to assess hydraulic and engine behavior
  
• Check for transmission responsiveness and steering clutch engagement
  
• Inspect undercarriage wear, especially sprockets and track tension
  
• Verify serial number to determine engine type and configuration
  
• Look for signs of oil leaks, especially around final drives and hydraulic cylinders
  

Oil analysis is ideal but may not be feasible in auction scenarios. In such cases, visual inspection and operational testing become critical.
Conclusion
Replacing a beloved TD6 with a Caterpillar D4H is not just a mechanical upgrade—it’s a generational shift. The D4H offers more horsepower, better ergonomics, and hydrostatic precision, making it a worthy successor for small-scale farming and land management.
While sentimental machines like the TD6 carry history, modern demands require reliability and efficiency. The D4H, with its proven track record and accessible maintenance, stands as a practical and powerful choice for those ready to move forward without forgetting where they started.