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The Legacy of the Caterpillar 955 Series
The Caterpillar 955 series track loaders were introduced in the mid-20th century as part of Caterpillar’s push to dominate the crawler loader market. The 955C, produced in the late 1950s, and the 955E, which followed in the early 1960s, were built on the 12A serial number platform and powered by the D315 diesel engine—a four-cylinder workhorse known for its torque and reliability.
Caterpillar, founded in 1925, had by this time become a global leader in earthmoving equipment. The 955 series was widely used in construction, logging, and municipal work. Tens of thousands of units were sold across North America and Europe, and many remain in service today, often in private hands or small fleets. The transition from the 955C to the 955E marked a shift from D4-size undercarriages to D6-size, improving traction and load capacity.
What Is a Balancer and Why Does It Matter
In four-cylinder diesel engines like the D315, vibration control is critical. The balancer assembly—sometimes referred to as a counterbalance shaft or harmonic balancer—is designed to smooth out the engine’s firing pulses and reduce torsional vibration. These components are typically mounted inside the oil pan and driven by the crankshaft gear.
The balancer spins at twice the crankshaft speed and uses weighted lobes to counteract the vertical and horizontal forces generated during combustion. Without it, the engine may suffer from excessive vibration, leading to fatigue in mounts, brackets, and even the block itself.
Terminology Explained
Installing a balancer is not as simple as bolting it in place. It must be timed precisely to the crankshaft to ensure the counterweights are synchronized with piston movement. Misalignment can worsen vibration and cause mechanical damage.
Steps for proper installation include:
Field Anecdote and Practical Insight
A retired operator in Alaska acquired two Caterpillar loaders—one 955C in pieces and one 955E mostly intact. The 955C, nicknamed “Old Bones,” came with a rebuilt pony engine and a reworked undercarriage but was missing key components, including a properly stored balancer. The 955E, by contrast, had simply “quit” one day but remained structurally sound.
Faced with a choice, the operator decided to prioritize the 955E for restoration, citing its complete chassis and smoother engine turnover. The balancer from the 955C was cleaned and preserved as a spare, pending further inspection. This decision reflects a common strategy in vintage equipment restoration: start with the most complete machine and use the other as a donor.
Manuals and Documentation Challenges
Finding accurate service manuals for the 955 series can be difficult. The most valuable document is Service Information Form #3225, which covers the unique aspects of the 955 compared to the D4 tractor. Other useful references include:
Recommendations for Restoration Projects
Modern engines use electronically controlled balance systems and vibration dampers, but the principles remain the same. The balancer in a D315 engine is a mechanical solution to a universal problem—how to make a four-cylinder engine run smoothly under load.
In newer Caterpillar models, vibration control is integrated into the crankshaft and engine mounts, reducing the need for separate balancer shafts. However, the simplicity and durability of the D315 design make it ideal for restoration and long-term use in low-speed, high-torque applications.
Conclusion
The balancer assembly in Caterpillar 955C and 955E loaders is a critical component for engine longevity and operator comfort. Proper installation, timing, and maintenance are essential, especially when restoring machines from parts. With the right tools, documentation, and patience, even a rusty balancer found in a bucket can be brought back to life—just like the loaders themselves. These machines, built in an era of mechanical honesty, continue to teach valuable lessons about engineering, perseverance, and the joy of bringing old iron back to work.
The Caterpillar 955 series track loaders were introduced in the mid-20th century as part of Caterpillar’s push to dominate the crawler loader market. The 955C, produced in the late 1950s, and the 955E, which followed in the early 1960s, were built on the 12A serial number platform and powered by the D315 diesel engine—a four-cylinder workhorse known for its torque and reliability.
Caterpillar, founded in 1925, had by this time become a global leader in earthmoving equipment. The 955 series was widely used in construction, logging, and municipal work. Tens of thousands of units were sold across North America and Europe, and many remain in service today, often in private hands or small fleets. The transition from the 955C to the 955E marked a shift from D4-size undercarriages to D6-size, improving traction and load capacity.
What Is a Balancer and Why Does It Matter
In four-cylinder diesel engines like the D315, vibration control is critical. The balancer assembly—sometimes referred to as a counterbalance shaft or harmonic balancer—is designed to smooth out the engine’s firing pulses and reduce torsional vibration. These components are typically mounted inside the oil pan and driven by the crankshaft gear.
The balancer spins at twice the crankshaft speed and uses weighted lobes to counteract the vertical and horizontal forces generated during combustion. Without it, the engine may suffer from excessive vibration, leading to fatigue in mounts, brackets, and even the block itself.
Terminology Explained
- Balancer Shaft: A rotating shaft with offset weights used to cancel out engine vibrations.
- Dynamic Load: The fluctuating forces generated by moving parts, especially during combustion.
- Lanchester Balancer: A type of dual-shaft system developed by the Lanchester brothers in the early 20th century, often used in four-cylinder engines.
Installing a balancer is not as simple as bolting it in place. It must be timed precisely to the crankshaft to ensure the counterweights are synchronized with piston movement. Misalignment can worsen vibration and cause mechanical damage.
Steps for proper installation include:
- Clean and inspect the balancer for rust, wear, and free movement
- Align timing marks on the balancer gear with the crankshaft gear
- Torque mounting bolts to factory specifications
- Verify rotation direction and clearance within the oil pan
- Prime the balancer bearings with oil before startup
Field Anecdote and Practical Insight
A retired operator in Alaska acquired two Caterpillar loaders—one 955C in pieces and one 955E mostly intact. The 955C, nicknamed “Old Bones,” came with a rebuilt pony engine and a reworked undercarriage but was missing key components, including a properly stored balancer. The 955E, by contrast, had simply “quit” one day but remained structurally sound.
Faced with a choice, the operator decided to prioritize the 955E for restoration, citing its complete chassis and smoother engine turnover. The balancer from the 955C was cleaned and preserved as a spare, pending further inspection. This decision reflects a common strategy in vintage equipment restoration: start with the most complete machine and use the other as a donor.
Manuals and Documentation Challenges
Finding accurate service manuals for the 955 series can be difficult. The most valuable document is Service Information Form #3225, which covers the unique aspects of the 955 compared to the D4 tractor. Other useful references include:
- D315 Engine Service Manual
- 955 12A Parts Manual
- 955 Operation and Maintenance Guide
Recommendations for Restoration Projects
- Always inspect balancer shafts for wear, rust, and bearing integrity
- Do not install a balancer without verifying timing and gear alignment
- Use service manuals to guide installation and torque specs
- Consider ultrasonic cleaning or bead blasting for heavily corroded parts
- Replace seals and gaskets during reassembly to prevent oil leaks
Modern engines use electronically controlled balance systems and vibration dampers, but the principles remain the same. The balancer in a D315 engine is a mechanical solution to a universal problem—how to make a four-cylinder engine run smoothly under load.
In newer Caterpillar models, vibration control is integrated into the crankshaft and engine mounts, reducing the need for separate balancer shafts. However, the simplicity and durability of the D315 design make it ideal for restoration and long-term use in low-speed, high-torque applications.
Conclusion
The balancer assembly in Caterpillar 955C and 955E loaders is a critical component for engine longevity and operator comfort. Proper installation, timing, and maintenance are essential, especially when restoring machines from parts. With the right tools, documentation, and patience, even a rusty balancer found in a bucket can be brought back to life—just like the loaders themselves. These machines, built in an era of mechanical honesty, continue to teach valuable lessons about engineering, perseverance, and the joy of bringing old iron back to work.
