Repairing Track Tension Springs on the Caterpillar 951C Loader

[MikePhua]

The 951C and Caterpillar’s Track Loader Legacy
The Caterpillar 951C was introduced in the 1970s as part of CAT’s evolution in crawler loaders, combining the ruggedness of dozers with the versatility of front-end loaders. Powered by a turbocharged 3304 diesel engine producing around 100 horsepower, the 951C featured a direct drive transmission, hydraulic loader linkage, and a sealed and lubricated track system. With an operating weight near 30,000 lbs and a bucket capacity of approximately 1.5 cubic yards, it became a staple in construction, demolition, and land clearing.
Caterpillar’s track loaders were widely adopted across North America and Europe, with the 951 series selling in the tens of thousands. The 951C represented a refinement in operator comfort and serviceability, but like all tracked machines, its undercarriage components—especially the recoil spring assemblies—were subject to wear and fatigue.
Identifying Broken Recoil Springs and Their Risks
The recoil spring, also known as the track tension spring, is a critical part of the undercarriage system. It absorbs shock and maintains proper track tension by allowing the front idler to move under load. When these springs break, several issues arise:

• Loss of track tension control
  
• Increased wear on track links and rollers
  
• Risk of track derailment during operation
  
• Reduced ability to absorb impact from uneven terrain
  

In one case, both recoil springs on a 951C were found broken during a repainting project. Despite the tracks being adjusted to spec, the broken springs still held residual tension, complicating removal and raising safety concerns.
Safe Removal and Replacement Strategies
Removing broken recoil springs requires caution due to residual tension and the risk of sudden release. Several approaches exist:

• Torch cutting the broken spring in place to release tension safely
  
• Using the loader bucket and a block to compress the idler and remove the keeper
  
• Driving out the master pin to split the track and remove the recoil assembly
  
• Employing a spring compressor or hydraulic press to disassemble the unit
  

Operators must identify the master pin, typically marked with dimples on both ends, and use a heavy hammer or press to drive it out. On older machines, heat may be necessary to loosen seized pins. Some technicians recommend collapsing the idler and walking the track off with side tension, though this method is labor-intensive and risky without proper equipment.
Component Inspection Beyond the Springs
Replacing the springs alone may not resolve all issues. The recoil assembly includes:

• Sliders that guide the idler movement
  
• Grease cylinder and piston
  
• Keeper plates and bushings
  
• Mounting brackets and seals
  

Sliders are often rust-pitted or worn, causing binding and uneven tension. These should be inspected and replaced if necessary. Grease fittings must be cleaned and tested to ensure proper lubrication of the recoil cylinder.
Parts Availability and Cost Considerations
Aftermarket suppliers offer replacement springs for the 951C, with prices ranging from $500 to $600 per pair. OEM parts may be available through dealers like HO Penn or Offroad Equipment. Additional components such as drive pucks (flex coupler discs) cost around $77 each and can be replaced from the top without dropping the belly pan.
Operators on a budget may defer full repair and continue light-duty work with adjusted tracks, but this is not recommended for heavy use. Running with broken springs increases the risk of track damage and may lead to more expensive repairs later.
A Story from the Field
In New York, a newly acquired 951C was found to have broken recoil springs during a restoration. The owner debated whether to split the track or attempt removal with the bucket. After consulting with a local mobile repair technician equipped with a 150-ton pin press, he decided to defer the repair and continue light work. Meanwhile, he sourced springs online and fabricated a safety strut for future maintenance. The loader was repainted using dented cans of Rustoleum safety yellow mixed with red tint, giving it a fresh look while awaiting mechanical upgrades.
Preventive Maintenance and Undercarriage Care
To extend the life of track components:

• Inspect recoil springs annually for cracks or corrosion
  
• Maintain proper track tension using grease cylinder adjustments
  
• Clean belly pans to prevent overheating and fire hazards
  
• Use anti-seize on belly pan bolts for easier future access
  
• Block and support the machine securely during undercarriage work
  

Dropping the belly pan reveals hidden issues such as loose hydraulic hoses, oil buildup, and dropped tools. Though unpleasant, this task improves cooling and reduces the risk of damage from debris.
Conclusion
Repairing broken track tension springs on a Caterpillar 951C loader is a demanding but necessary task to preserve undercarriage integrity and operational safety. While temporary adjustments may suffice for light work, proper removal and replacement—ideally with the right tools and support—ensures long-term reliability. In the world of tracked machines, tension isn’t just mechanical—it’s the difference between smooth operation and costly downtime.