CAT 931 Track Loader Remains a Durable Workhorse but Requires Careful Attention to Powertrain Components

[MikePhua]

The Development and Legacy of the CAT 931
The Caterpillar 931 track loader was introduced in the 1970s as part of Caterpillar’s push to offer compact, versatile machines for construction, agriculture, and light demolition. Positioned between the smaller 933 and the heavier 941, the 931 was designed to deliver maneuverability with enough breakout force to handle moderate excavation and loading tasks. It featured a hydrostatic drive system in later models and a torque converter transmission in earlier variants, such as the 931B and 931C.
Caterpillar Inc., founded in 1925, has long been a global leader in heavy equipment manufacturing. The 931 series was produced during a time when mechanical simplicity and field serviceability were prioritized. Thousands of units were sold globally, and many remain in operation today due to their rugged construction and availability of aftermarket parts.
Torque Converter Issues and Replacement Challenges
One of the most critical components in the early CAT 931 models is the torque converter, which transmits engine power to the transmission while allowing for smooth gear changes and load absorption. Over time, torque converters can fail due to:

• Internal clutch wear
  
• Fluid contamination
  
• Overheating from clogged coolers
  
• Seal degradation leading to pressure loss
  

When a torque converter fails, symptoms include sluggish movement, poor pushing power, excessive engine revving without corresponding track response, and overheating. Replacing the torque converter is a labor-intensive process, often requiring the removal of the loader frame or splitting the machine at the bell housing.
Sourcing Rebuilt or New Torque Converters
Finding a replacement torque converter for a CAT 931—especially one with a serial number in the 78U range—can be challenging due to the machine’s age. Options include:

• Contacting specialized salvage yards that deal in vintage Caterpillar parts
  
• Reputable rebuilders who offer remanufactured torque converters with updated internals
  
• Online heavy equipment parts exchanges or auctions
  
• Custom rebuild services that refurbish the original unit with new seals, bearings, and clutch packs
  

When sourcing a rebuilt unit, ensure it includes a warranty and verify compatibility with your specific serial number. Some rebuilders may require the old core in exchange.
Installation Tips and Precautions
When installing a new or rebuilt torque converter:

• Flush the transmission and cooler lines thoroughly to remove debris
  
• Replace all associated seals and gaskets
  
• Check the flex plate and input shaft for wear or misalignment
  
• Use the correct torque specs for mounting bolts to avoid warping the housing
  
• Refill with the manufacturer-recommended transmission fluid and monitor pressure after startup
  

Anecdote from the Field
A contractor in North Carolina shared that after months of sluggish performance, his 931 loader finally lost all forward motion. Upon inspection, the torque converter had suffered internal clutch failure. After sourcing a rebuilt unit from a Tennessee-based supplier, he completed the swap in three days with the help of a local mechanic. The machine returned to full function, and he noted improved responsiveness and reduced fuel consumption.
Conclusion
The CAT 931 remains a reliable and capable track loader when properly maintained. However, its torque converter is a known weak point in aging units. Operators should monitor for signs of transmission inefficiency and act quickly to prevent further damage. With the right parts and attention to detail, even a decades-old 931 can continue to serve effectively in modern job sites.