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The Cat 931 Series and Its Steering System
The Caterpillar 931 series track loader was introduced in the 1970s as a compact, versatile machine for excavation, grading, and material handling. The 931B variant, produced in the early 1980s, featured a 3204 four-cylinder diesel engine, a hydrostatic transmission, and a mechanical steering clutch and brake system. Caterpillar, founded in 1925, had by then become the global benchmark for tracked earthmoving equipment. The 931B was widely adopted by contractors and municipalities for its balance of power and maneuverability, with thousands sold across North America and Europe.
The steering system on the 931B uses a combination of dry steering clutches and band-type brakes. Each side of the machine has a foot pedal that first disengages the clutch and then applies the brake, allowing the machine to pivot or counter-rotate. This system is purely mechanical and relies on precise linkage adjustment and clean, functional clutch packs.
Symptoms of Right Turn Failure
In one case, a 1978 Cat 931B with low hours exhibited a complete inability to turn right. The machine drove straight, pulled loads evenly, and showed no signs of power loss. However, pressing the right steering pedal had no effect—no clutch disengagement, no braking, and no directional change. The left side functioned normally, allowing left turns and gradual curves.
This behavior suggests that the right steering clutch is not disengaging, preventing the brake from taking effect. The brake band may still be functional, but without clutch release, the track continues to drive forward under power.
Initial Checks and Linkage Inspection
The first step in diagnosing this issue is to inspect the mechanical linkage between the pedal and the clutch control shaft. On the 931B, this involves removing the floorboards and observing the movement of the control shaft as the pedal is pressed. If the shaft does not rotate or moves only partially, the problem may lie in the linkage, pivot bushings, or pedal adjustment.
In this case, the linkage appeared intact and moved freely. The control valve cam and roller also showed no signs of wear or binding. This ruled out external mechanical faults and pointed toward an internal clutch issue.
Brake Adjustment Procedure
Before disassembling the clutch, technicians recommend adjusting the brake band to eliminate free play and confirm brake function. The procedure is as follows:
Hydraulic Steering Valve and Pressure Testing
Although the 931B uses mechanical clutches, it incorporates a hydraulic assist valve to reduce pedal effort. This valve contains a cam and roller mechanism that actuates a spool to direct oil to the clutch slave cylinder. If the roller develops a flat spot or the cam is worn, the clutch may not fully disengage.
To verify hydraulic function, technicians can test pressure at the slave cylinder port. The minimum pressure required to disengage the clutch is approximately 270 psi. A gauge reading below this threshold indicates a faulty valve, broken spring, or internal leak.
In this case, the operator observed strong flow from the test port when the pedal was pressed, suggesting that hydraulic pressure was present. However, without a gauge reading, the exact pressure remained unknown.
Internal Clutch Pack Failure
If all external components are functional, the most likely cause is a rusted or seized clutch pack. Over time, moisture can enter the housing and cause the steel plates to corrode and stick together. This prevents disengagement even when hydraulic pressure is applied.
Disassembly of the steering clutch involves:
Safety and Best Practices
When working on hydraulic systems, never use bare hands to check for leaks. High-pressure fluid can penetrate skin and cause serious injury. Always use a pressure gauge and wear protective gloves.
Also, note that early 931B models differ from the original 931 in steering valve design. Always refer to the correct service manual based on the full serial number. In this case, the machine was identified as a very early 931B (serial prefix 25Y), which uses a non-crossover steering valve.
Final Thoughts
A Cat 931B that won’t turn right is most often suffering from a stuck or non-releasing steering clutch. While linkage and brake adjustments should be checked first, internal inspection is often required. With proper diagnosis and careful disassembly, these machines can be restored to full functionality. The 931B remains a serviceable and straightforward loader, and its mechanical simplicity is both a challenge and an advantage for dedicated operators.
The Caterpillar 931 series track loader was introduced in the 1970s as a compact, versatile machine for excavation, grading, and material handling. The 931B variant, produced in the early 1980s, featured a 3204 four-cylinder diesel engine, a hydrostatic transmission, and a mechanical steering clutch and brake system. Caterpillar, founded in 1925, had by then become the global benchmark for tracked earthmoving equipment. The 931B was widely adopted by contractors and municipalities for its balance of power and maneuverability, with thousands sold across North America and Europe.
The steering system on the 931B uses a combination of dry steering clutches and band-type brakes. Each side of the machine has a foot pedal that first disengages the clutch and then applies the brake, allowing the machine to pivot or counter-rotate. This system is purely mechanical and relies on precise linkage adjustment and clean, functional clutch packs.
Symptoms of Right Turn Failure
In one case, a 1978 Cat 931B with low hours exhibited a complete inability to turn right. The machine drove straight, pulled loads evenly, and showed no signs of power loss. However, pressing the right steering pedal had no effect—no clutch disengagement, no braking, and no directional change. The left side functioned normally, allowing left turns and gradual curves.
This behavior suggests that the right steering clutch is not disengaging, preventing the brake from taking effect. The brake band may still be functional, but without clutch release, the track continues to drive forward under power.
Initial Checks and Linkage Inspection
The first step in diagnosing this issue is to inspect the mechanical linkage between the pedal and the clutch control shaft. On the 931B, this involves removing the floorboards and observing the movement of the control shaft as the pedal is pressed. If the shaft does not rotate or moves only partially, the problem may lie in the linkage, pivot bushings, or pedal adjustment.
In this case, the linkage appeared intact and moved freely. The control valve cam and roller also showed no signs of wear or binding. This ruled out external mechanical faults and pointed toward an internal clutch issue.
Brake Adjustment Procedure
Before disassembling the clutch, technicians recommend adjusting the brake band to eliminate free play and confirm brake function. The procedure is as follows:
- Locate the vertical hex adjuster rod on the right side
- Tighten the adjuster until firm resistance is felt
- Under the rear case, tighten the support bolts until snug
- Back off the support bolts one full turn and lock them
- Loosen the brake adjuster rod by 1½ turns (9 flats)
- Check pedal height and free play
Hydraulic Steering Valve and Pressure Testing
Although the 931B uses mechanical clutches, it incorporates a hydraulic assist valve to reduce pedal effort. This valve contains a cam and roller mechanism that actuates a spool to direct oil to the clutch slave cylinder. If the roller develops a flat spot or the cam is worn, the clutch may not fully disengage.
To verify hydraulic function, technicians can test pressure at the slave cylinder port. The minimum pressure required to disengage the clutch is approximately 270 psi. A gauge reading below this threshold indicates a faulty valve, broken spring, or internal leak.
In this case, the operator observed strong flow from the test port when the pedal was pressed, suggesting that hydraulic pressure was present. However, without a gauge reading, the exact pressure remained unknown.
Internal Clutch Pack Failure
If all external components are functional, the most likely cause is a rusted or seized clutch pack. Over time, moisture can enter the housing and cause the steel plates to corrode and stick together. This prevents disengagement even when hydraulic pressure is applied.
Disassembly of the steering clutch involves:
- Draining the final drive oil
- Removing the steering clutch housing cover
- Extracting the clutch pack and inspecting for rust, wear, or broken springs
- Cleaning and re-plating the steel discs if salvageable
- Replacing the pack if beyond repair
Safety and Best Practices
When working on hydraulic systems, never use bare hands to check for leaks. High-pressure fluid can penetrate skin and cause serious injury. Always use a pressure gauge and wear protective gloves.
Also, note that early 931B models differ from the original 931 in steering valve design. Always refer to the correct service manual based on the full serial number. In this case, the machine was identified as a very early 931B (serial prefix 25Y), which uses a non-crossover steering valve.
Final Thoughts
A Cat 931B that won’t turn right is most often suffering from a stuck or non-releasing steering clutch. While linkage and brake adjustments should be checked first, internal inspection is often required. With proper diagnosis and careful disassembly, these machines can be restored to full functionality. The 931B remains a serviceable and straightforward loader, and its mechanical simplicity is both a challenge and an advantage for dedicated operators.
