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The CAT 931B and Its Mechanical Simplicity
The Caterpillar 931B track loader was introduced in the late 1970s as part of CAT’s push to offer mid-sized crawler loaders for construction, demolition, and land clearing. With an operating weight of around 16,000 pounds and powered by the reliable CAT 3204 diesel engine, the 931B became a staple in municipal fleets and small contractor yards. Its mechanical transmission, cable-linked controls, and straightforward hydraulic layout made it easy to maintain and repair without specialized tools.
By the mid-1980s, thousands of 931Bs had been sold across North America and Europe. Though later models introduced more electronics and emissions controls, the 931B remained popular for its ruggedness and rebuildability.
Sourcing Gauges, Filters, and Electrical Components
Owners of older machines like the 931B often face challenges sourcing small parts such as gauges, switches, and filters. Fortunately, many components are interchangeable with automotive-grade parts, especially in 12-volt systems. For example:
Custom Dash Panel Fabrication
Many 931Bs suffer from cracked or missing dash panels due to age and exposure. Rebuilding the dash is a common project, with several material options:
Terminology Notes
Tilt cylinders often require seal kit replacements due to leakage or sluggish movement. After reassembly, air trapped in the hydraulic lines can cause erratic behavior. Bleeding the system involves cycling the cylinders fully several times with the reservoir cap loosened. If movement remains inconsistent, inspect for internal bypass or damaged piston seals.
Clutch and Brake Overhaul Considerations
The 931B uses mechanical clutches and brakes linked to the steering levers. Rebuilding these systems requires:
Field Stories and Practical Advice
One owner in North Carolina rebuilt his 931B over several months, starting with the dash and gauges, then progressing to hydraulic repairs and clutch work. He noted that many parts were hard to find or mislabeled online, requiring patience and creativity. His use of PVC pipe to mount an amp gauge was praised for its simplicity and effectiveness.
Another operator discovered that a CAT gauge he purchased was too large, interfering with the foot controls. He later found the correct part number in his original parts book—highlighting the importance of documentation.
Conclusion
Rebuilding small parts on a CAT 931B is a rewarding process that blends mechanical skill with resourcefulness. Whether fabricating a dash from plexiglass, sourcing automotive gauges, or bleeding tilt cylinders, each step brings the machine closer to full functionality. With proper planning and a willingness to adapt, even a battered loader can be restored to reliable service.
The Caterpillar 931B track loader was introduced in the late 1970s as part of CAT’s push to offer mid-sized crawler loaders for construction, demolition, and land clearing. With an operating weight of around 16,000 pounds and powered by the reliable CAT 3204 diesel engine, the 931B became a staple in municipal fleets and small contractor yards. Its mechanical transmission, cable-linked controls, and straightforward hydraulic layout made it easy to maintain and repair without specialized tools.
By the mid-1980s, thousands of 931Bs had been sold across North America and Europe. Though later models introduced more electronics and emissions controls, the 931B remained popular for its ruggedness and rebuildability.
Sourcing Gauges, Filters, and Electrical Components
Owners of older machines like the 931B often face challenges sourcing small parts such as gauges, switches, and filters. Fortunately, many components are interchangeable with automotive-grade parts, especially in 12-volt systems. For example:
- Automotive gauges from NAPA or Carquest can be used for oil pressure, temperature, and voltage, provided the sending units match the voltage range.
- Mechanically actuated gauges (e.g., capillary tube temperature gauges) are voltage-independent except for the backlight bulb.
- CAT filters remain competitively priced and are often more reliable than aftermarket options. Fuel filters from third-party brands have been known to split under pressure, especially on engines like the CAT 3304.
Custom Dash Panel Fabrication
Many 931Bs suffer from cracked or missing dash panels due to age and exposure. Rebuilding the dash is a common project, with several material options:
- Plywood is easy to cut and drill but lacks durability and weather resistance.
- Plexiglass offers visibility and flexibility, allowing precise switch alignment. It can be shaped with basic tools and painted to match CAT yellow.
- Sheet metal provides strength but requires drill presses or punch tools for clean holes.
Terminology Notes
- Sending Unit: A sensor that converts mechanical pressure or temperature into an electrical signal for a gauge.
- Capillary Tube Gauge: A mechanical temperature gauge using a sealed tube filled with fluid or gas.
- Detent: A mechanical catch that holds a control lever in position.
- Tilt Cylinder: Hydraulic actuator controlling the bucket’s tilt angle.
Tilt cylinders often require seal kit replacements due to leakage or sluggish movement. After reassembly, air trapped in the hydraulic lines can cause erratic behavior. Bleeding the system involves cycling the cylinders fully several times with the reservoir cap loosened. If movement remains inconsistent, inspect for internal bypass or damaged piston seals.
Clutch and Brake Overhaul Considerations
The 931B uses mechanical clutches and brakes linked to the steering levers. Rebuilding these systems requires:
- Removing the cover plate over the transmission tunnel
- Inspecting clutch discs and brake bands for wear
- Replacing springs and detents as needed
- Adjusting linkage tension to ensure smooth engagement
Field Stories and Practical Advice
One owner in North Carolina rebuilt his 931B over several months, starting with the dash and gauges, then progressing to hydraulic repairs and clutch work. He noted that many parts were hard to find or mislabeled online, requiring patience and creativity. His use of PVC pipe to mount an amp gauge was praised for its simplicity and effectiveness.
Another operator discovered that a CAT gauge he purchased was too large, interfering with the foot controls. He later found the correct part number in his original parts book—highlighting the importance of documentation.
Conclusion
Rebuilding small parts on a CAT 931B is a rewarding process that blends mechanical skill with resourcefulness. Whether fabricating a dash from plexiglass, sourcing automotive gauges, or bleeding tilt cylinders, each step brings the machine closer to full functionality. With proper planning and a willingness to adapt, even a battered loader can be restored to reliable service.
