Reviving the CAT 931B: Diagnosing Steering and Hydraulic Leaks

[MikePhua]

Introduction to the CAT 931B Track Loader
The Caterpillar 931B track loader is a workhorse in its class—a compact yet powerful crawler loader designed for general construction, utility work, and farm operations. With its straightforward mechanical systems and rugged undercarriage, the 931B has found a second life in private yards and small-scale commercial jobs across the globe. But like any aging machine, it brings with it a series of mechanical quirks, often centered around hydraulic leaks and steering issues.
Understanding the Steering System and Its Vulnerabilities
The 931B features a clutch-brake steering system. This system relies on two steering clutch packs—left and right—to allow the machine to pivot. When the operator pulls back on one of the steering levers, the corresponding clutch disengages, and the brake slows or stops the track on that side, enabling a turn.
Over time, the most common problems involve:

• Loss of clutch engagement due to worn friction discs or weak springs
  
• Brake fade or failure from fluid contamination or mechanical wear
  
• Sticking levers caused by rusty linkage or hardened grease
  
• Hydraulic seepage entering the steering clutch compartment, leading to slipping
  

One particular user noted that the left steering clutch was nearly ineffective and that engaging it yielded no response. This kind of behavior is typically indicative of oil contamination—when the clutch discs become saturated with hydraulic or transmission oil, their ability to grip diminishes drastically. It’s not a matter of force but of friction. Once the discs are soaked, they slip instead of engaging.
Clues from Hydraulic Leaks
Hydraulic leaks in older Caterpillar machinery are almost a given. However, discerning where they originate and what systems they affect is vital to planning repairs.
In this case, fluid was found dripping from the belly pan, near the left steering clutch housing. This strongly suggests:

• Input shaft seal failure, allowing transmission oil to migrate into the steering clutch compartment
  
• Hydraulic line or fitting failure, often from chafing or fatigue near the tank or control valve
  
• Brake rod seals or cover gasket leaks
  

Adding to the complexity is the loader’s hydraulic tank itself. One helpful voice pointed out that the hydraulic reservoir has a known weak spot on top—where hoses are clamped down tight. Over-tightened clamps can crack the tank, creating a slow and deceptive leak. Compounding this is the location of the belly pan—it collects fluid from almost anywhere, making it hard to visually trace leaks without dropping the pan.
Troubleshooting Strategies
When tackling these issues, the following strategies have proven effective:

• Use UV dye in the hydraulic and transmission fluids to trace leak origin
  
• Pull inspection covers on the steering clutch housing to check for oil contamination
  
• Check hydraulic tank welds and hose clamps for stress fractures
  
• Replace steering clutch discs and clean the compartment if contamination is confirmed
  

A seasoned mechanic also recommended a less invasive approach: drill a small inspection hole near the bottom of the steering clutch housing and install a magnetic plug. Over time, the plug will collect fine metal particles if the clutch is wearing excessively, and oil presence can be confirmed by a simple dipstick.
Lessons from the Field
A memorable story comes from a small logging operation in British Columbia. The owner ran a 931B in rough terrain and started noticing a loss of left-turning power. Assuming it was just clutch wear, he continued operating the machine—until one day it lost all steering on that side. When he finally opened it up, he discovered the clutch pack was submerged in a mixture of transmission oil and brake lining sludge. It turned out a minor input shaft seal had failed six months prior. The delay cost him a new clutch pack and significant downtime during peak season.
Recommended Fixes and Precautions
The consensus among experienced operators and mechanics includes the following action points:

• Replace seals preemptively: Once one fails, others are likely close behind.
  
• Keep belly pans clean: Fluid build-up hides early warning signs.
  
• Install a filter on the hydraulic breather cap to reduce dust and moisture ingress.
  
• Upgrade to modern, heat-resistant rubber hoses if originals are still installed.
  
• Check venting: A clogged transmission case vent can increase internal pressure and blow out seals.
  

Summary of Components to Inspect or Replace

• Input shaft seals (transmission side)
  
• Brake rod seals
  
• Steering clutch friction and steel discs
  
• Hydraulic tank return lines and clamps
  
• Control valve O-rings and banjo fittings
  
• Top welds and seams of hydraulic tank
  

Conclusion
The CAT 931B remains a dependable machine when maintained properly. Steering and hydraulic leak issues, though common, are entirely manageable with patience and methodical troubleshooting. A proactive approach to replacing aging seals and cleaning internal compartments can extend the life of these machines dramatically. For owners of legacy Caterpillar loaders, the battle against time is ongoing—but not unwinnable. With diligence and mechanical intuition, the 931B continues to move dirt and push boundaries long past its design age.