CAT 963B Track Tension Failure and Grease Cylinder Troubleshooting

[MikePhua]

The CAT 963B and Its Undercarriage Design
The Caterpillar 963B track loader was introduced in the early 1990s as an evolution of the original 963 series, offering improved hydraulic performance, enhanced operator comfort, and a more robust undercarriage system. Built for versatility in construction, demolition, and land clearing, the 963B featured a hydrostatic drive, a 3204 turbocharged diesel engine, and a sealed and lubricated track system designed to reduce wear and extend service intervals.
The undercarriage includes a grease-filled recoil mechanism that maintains track tension by pushing the idler forward. This system relies on a grease cylinder, a tension piston, and a spring-loaded recoil assembly. When functioning properly, adding grease through the tension fitting increases pressure, extending the idler and tightening the track.
Symptoms of a Failed Track Tensioning System
When the track fails to tighten and refuses to accept grease, several mechanical issues may be at play. Common symptoms include:

• Excessive track sag or derailment during turns
  
• Grease gun resistance or inability to inject grease
  
• Visible leakage around the tension cylinder or fitting
  
• Idler movement that does not respond to grease pressure
  
• Audible popping or clunking from the recoil spring housing
  

Terminology notes:

• Grease Cylinder: A sealed chamber that uses injected grease to push the idler forward.
  
• Recoil Spring: Absorbs shock and maintains tension under dynamic loads.
  
• Tension Fitting: A zerk-style grease port used to inject grease into the cylinder.
  
• Idler: The front wheel of the track assembly that adjusts position to maintain tension.
  

Root Causes and Diagnostic Strategy
When grease cannot be injected and the track remains loose, technicians should investigate the following:

• Damaged Tension Fitting
  The fitting may be clogged, cross-threaded, or internally broken. Replace with a new zerk fitting and test grease flow.
  
• Blown Seal Inside the Cylinder
  Internal seals may rupture, allowing grease to bypass the piston or escape into the recoil housing. Disassembly and seal replacement are required.
  
• Cracked Cylinder Housing
  Hairline fractures in the grease cylinder can prevent pressure buildup. Inspect with dye penetrant or pressure test.
  
• Piston Seizure
  Rust or debris may cause the piston to seize inside the cylinder. Removal and cleaning may restore function.
  
• Grease Relief Valve Failure
  Some models include a relief valve to prevent over-pressurization. If stuck open, grease will escape without building tension.
  

In one case, a contractor in Alberta discovered that the grease fitting had snapped off inside the cylinder port, blocking flow entirely. After extracting the broken fitting and flushing the port, the system accepted grease and restored track tension.
Repair Procedure and Component Notes
To repair a non-functioning tension system:

• Remove track guards and clean the area thoroughly
  
• Use a pipe wrench or spanner to loosen the tension cylinder cap
  
• Extract the piston and inspect for scoring, rust, or seal damage
  
• Replace seals with OEM or high-quality aftermarket kits
  
• Reassemble with fresh grease and test idler movement
  
• Monitor for leaks over the next 10 operating hours
  

Recommended parts include:

• Seal kit for 963B grease cylinder
  
• Replacement zerk fitting (high-pressure rated)
  
• Synthetic grease with anti-corrosion additives
  
• Torque wrench for proper reassembly
  

For machines operating in wet or abrasive environments, consider upgrading to a stainless steel fitting and applying thread sealant to prevent moisture intrusion.
Preventive Maintenance and Operator Tips
To avoid future tension failures:

• Grease the track tension system every 100–150 operating hours
  
• Inspect idler movement during daily walkarounds
  
• Avoid over-tightening, which can stress the recoil spring
  
• Clean fittings before greasing to prevent contamination
  
• Replace grease with fresh lubricant annually
  

Operators should be trained to recognize early signs of tension loss, such as increased track slap, uneven wear, or difficulty turning. A loose track not only accelerates undercarriage wear but also increases the risk of derailment and downtime.
In 2023, a fleet manager in Georgia implemented a quarterly undercarriage inspection protocol across all 963B units. The program reduced tension-related failures by 60% and extended track life by an average of 800 hours.
Conclusion
Track tension issues in the CAT 963B often stem from grease cylinder failure, seal degradation, or blocked fittings. While the system is mechanically simple, its reliability depends on regular maintenance and prompt diagnosis. With proper tools, replacement parts, and attention to detail, technicians can restore full function and prevent costly undercarriage damage. The 963B remains a powerful and dependable machine—provided its tension system is kept in check.