Restoring a Caterpillar 955K Track Loader for Ranch Work

[MikePhua]

The Legacy of the 955K
Caterpillar’s 955K crawler loader was introduced in the late 1960s as part of the company’s evolution in mid-size track loaders. Designed for versatility in earthmoving, land clearing, and material handling, the 955K featured a D330C diesel engine producing around 115 horsepower, paired with a powershift transmission and a rugged undercarriage. The machine weighed approximately 32,000 lbs and offered a bucket capacity of 1.5 to 2 cubic yards depending on configuration.
Caterpillar, founded in 1925, had by then become a global leader in heavy equipment. The 955K was a popular choice for contractors and landowners alike, with thousands sold across North America. Its successor, the 955L, introduced the 3304 engine and refined hydraulics, but the K model remained a workhorse in the field for decades.
Auction Find and Initial Assessment
One operator acquired a well-worn 955K at a local auction with plans to use it for brush clearing on a hunting ranch. The machine had undergone several modifications, including the installation of a dozer blade from a D5 or D6 in place of the original bucket, which was still in good condition. The loader arms had been patched with heavy steel, preventing the original safety bar from engaging, prompting the fabrication of a custom support bar to safely work beneath the raised arms.
Terminology annotation:
- Loader Arms: The hydraulic arms that raise and lower the bucket or blade. - Safety Bar: A mechanical lockout device used to secure the loader arms during maintenance. - Guillotine Risk: A colloquial term for the danger posed by unsupported loader arms falling unexpectedly.
The undercarriage appeared solid, but the left track sagged despite repeated greasing, suggesting a failed recoil spring or damaged tensioner piston. This issue required immediate attention to prevent derailment or uneven wear.
Cooling System Overhaul and Radiator Discovery
During initial operation, the machine overheated, forcing multiple shutdowns. Inspection revealed coolant spraying from pinholes in the radiator core, which was heavily clogged and partially blocked. Upon disassembly, the operator discovered that the radiator had been replaced with one from a later 955L model, including a full-length hydraulic cooler that was not connected and occupied valuable space.
The decision was made to rebuild the radiator using the original top and bottom tanks and a new core of correct dimensions. Several bolts broke during disassembly, requiring thread repair and careful reassembly. The hydraulic cooler was removed to restore airflow and cooling efficiency.
Terminology annotation:
- Radiator Core: The central section of the radiator where coolant flows and heat is dissipated. - Hydraulic Cooler: A heat exchanger used to cool hydraulic fluid, often integrated with the radiator in heavy equipment. - Stop Leak: A chemical additive used to seal minor leaks in cooling systems, which can cause long-term clogging and corrosion.
Field mechanics often warn against excessive use of stop leak products, as they can block narrow passages in the radiator and oil cooler, reducing thermal efficiency and increasing the risk of overheating.
Engine Identification and Filter Conversion
The machine’s engine was initially believed to be a D330C, but debate arose over whether it might be a 3304, given the serial number and modifications. The 85J prefix on the machine indicated a late-model 955K, just before the transition to the L series. According to Caterpillar production data, the switch to the 3304 engine occurred at serial number 85J4672, confirming that this unit likely retained the original D330C.
The operator sought to convert the oil filter system from a cartridge-style element to a spin-on filter for easier maintenance. The existing filter base was leaking and outdated. While some conversions are straightforward—such as using a D7G filter base on a D7F engine—the compatibility between early and late 3304 oil coolers required verification before sourcing parts.
Terminology annotation:
- Spin-On Filter: A self-contained oil filter that screws onto a threaded base, simplifying replacement. - Cartridge Filter: A replaceable filter element housed within a permanent base, requiring more labor to service. - Oil Cooler: A component that regulates engine oil temperature by transferring heat to the coolant or ambient air.
Operators converting filter systems should confirm mounting flange dimensions, oil flow direction, and pressure ratings to avoid mismatched components that could restrict flow or cause leaks.
Loader Blade and Undercarriage Modifications
The dozer blade mounted to the 955K was adapted from a larger machine, requiring custom brackets and altered geometry. Observers noted cut-down dozer shoes and unusual blade supports, suggesting extensive field modification. While functional, such changes can affect balance, hydraulic response, and visibility.
The undercarriage appeared to be from a D5, which shares similar dimensions but may differ in sprocket pitch and recoil spring strength. Matching track components across models requires careful measurement of:

• Track pitch (distance between pin centers)
  
• Shoe width and grouser height
  
• Idler and sprocket alignment
  
• Recoil spring preload and tensioner stroke
  

Terminology annotation:
- Track Pitch: The spacing between track links, critical for sprocket engagement. - Recoil Spring: A spring mechanism that maintains track tension and absorbs shock. - Grouser: The raised ridge on a track shoe that provides traction.
Improper undercarriage matching can lead to accelerated wear, misalignment, and reduced pulling power.
Lessons from the Field and Practical Advice
One technician recalled converting a D7F to a spin-on filter using parts from a D7G, noting that the oil cooler flange matched perfectly. However, he cautioned that not all CAT engines share interchangeable components, especially across series transitions. Another operator emphasized the importance of verifying engine serial numbers, which are often stamped on the left rear block below the head, though they may be obscured by grime or missing tags.
Recommendations for restoration projects:

• Document all serial numbers and component origins
  
• Avoid mixing cooling system parts across models without verifying airflow and fit
  
• Use thread chasers and anti-seize on radiator bolts to prevent future breakage
  
• Install a loader arm support bar if the original safety system is compromised
  
• Pressure test the radiator and oil cooler before reassembly
  

Conclusion
Restoring a Caterpillar 955K for ranch work is a rewarding challenge that blends mechanical skill with historical appreciation. From cooling system rebuilds to undercarriage diagnosis and filter upgrades, each step reveals the machine’s legacy and the ingenuity of its operators. With careful planning and attention to detail, even a heavily modified loader can return to productive service—clearing brush, moving earth, and carrying the spirit of old iron into new terrain.