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The Caterpillar 955 track loader is a classic machine from an era when mechanical reliability mattered more than electronics. Many units built in the 1960s and 1970s are still working today on farms, small construction sites, and land‑clearing projects. Despite their durability, age and infrequent use can cause steering issues, especially when the machine relies on a combination of mechanical linkages and hydraulic assistance. One common symptom is intermittent stiffness in the steering clutches, where the machine may steer easily at first but suddenly become extremely difficult to turn.
A real‑world case illustrates this perfectly: a 955 that steered normally at startup but became nearly impossible to turn after a short period of operation, with no consistent pattern to the stiffness. The eventual solution was surprisingly simple—low transmission oil—but the path to that discovery highlights how these systems behave and what owners should check first.
Development Background of the Caterpillar 955
The 955 series was one of Caterpillar’s most successful track loaders, produced across multiple generations from the 1950s through the 1980s. Key design goals included:
Terminology notes:
Symptoms of Steering Stiffness
The reported machine exhibited several key symptoms:
Likely Causes of Intermittent Steering Stiffness
Several issues can cause steering stiffness on a Caterpillar 955, especially on older machines.
Low Transmission Oil
The actual cause in the referenced case was simply low transmission oil. Once the operator refilled the system with the correct fluid, steering returned to normal immediately.
Low oil affects:
Contaminated or Thickened Oil
Old oil can thicken, especially in machines that sit unused for long periods. Thick oil reduces hydraulic flow and can cause sluggish or stiff steering.
Clogged Screens or Filters
Some older Caterpillar machines include internal screens that can become clogged with debris or sludge. A clogged screen restricts oil flow, causing intermittent steering stiffness. One mechanic in the discussion recalled such a screen on older models.
Rust or Debris in Linkages
Mechanical linkages connecting the steering levers to the clutch assemblies can accumulate rust, dirt, or hardened grease. This can cause inconsistent lever feel and sudden stiffness.
Air in the Hydraulic System
If the system draws air due to low oil or a loose fitting, hydraulic assist becomes inconsistent. Air pockets can cause sudden stiffness followed by normal operation once the air clears.
Why Low Transmission Oil Causes These Symptoms
Transmission oil in a 955 serves multiple functions:
Field Experiences and Anecdotes
Operators of older Caterpillar machines often share similar stories. One farmer recalled fighting stiff steering for weeks before discovering that a slow leak had drained half the transmission oil. Another mechanic remembered a 955 that steered perfectly in cold weather but became stiff in summer heat due to a partially clogged suction screen.
These stories highlight a common theme: simple fluid issues often masquerade as major mechanical failures.
Caterpillar Company Background
Caterpillar has been a leader in heavy equipment manufacturing for nearly a century. The 955 series played a major role in expanding Caterpillar’s presence in the track loader market. Its success stemmed from:
Practical Recommendations
Conclusion
Steering stiffness on a Caterpillar 955 is often caused by simple issues rather than major mechanical failures. In the documented case, low transmission oil was the culprit, and refilling the system restored normal steering immediately. Understanding how the steering and transmission systems interact helps operators diagnose problems quickly and avoid unnecessary repairs. With proper maintenance and attention to fluid levels, the 955 remains a reliable and capable machine even decades after its introduction.
A real‑world case illustrates this perfectly: a 955 that steered normally at startup but became nearly impossible to turn after a short period of operation, with no consistent pattern to the stiffness. The eventual solution was surprisingly simple—low transmission oil—but the path to that discovery highlights how these systems behave and what owners should check first.
Development Background of the Caterpillar 955
The 955 series was one of Caterpillar’s most successful track loaders, produced across multiple generations from the 1950s through the 1980s. Key design goals included:
- A rugged undercarriage based on Caterpillar crawler tractors
- A mechanical steering clutch and brake system
- A torque converter or direct‑drive transmission depending on model
- A loader linkage capable of heavy digging and material handling
Terminology notes:
- Steering clutch: A friction clutch that disengages one track to turn the machine.
- Brake band: A mechanical brake that tightens around a drum to assist turning.
- Torque converter: A fluid coupling that multiplies torque and drives the transmission.
- Transmission oil: Hydraulic‑grade oil used to lubricate and power the steering and transmission systems.
Symptoms of Steering Stiffness
The reported machine exhibited several key symptoms:
- Steering began normally with light finger pressure
- After some operation, the steering clutches became extremely stiff
- Occasionally a “release point” could be felt, after which steering returned to normal
- Stiffness was inconsistent and unpredictable
- The machine became nearly impossible to steer after extended use
Likely Causes of Intermittent Steering Stiffness
Several issues can cause steering stiffness on a Caterpillar 955, especially on older machines.
Low Transmission Oil
The actual cause in the referenced case was simply low transmission oil. Once the operator refilled the system with the correct fluid, steering returned to normal immediately.
Low oil affects:
- Hydraulic assist pressure
- Lubrication of clutch components
- Cooling of the transmission
- Engagement of steering clutches
Contaminated or Thickened Oil
Old oil can thicken, especially in machines that sit unused for long periods. Thick oil reduces hydraulic flow and can cause sluggish or stiff steering.
Clogged Screens or Filters
Some older Caterpillar machines include internal screens that can become clogged with debris or sludge. A clogged screen restricts oil flow, causing intermittent steering stiffness. One mechanic in the discussion recalled such a screen on older models.
Rust or Debris in Linkages
Mechanical linkages connecting the steering levers to the clutch assemblies can accumulate rust, dirt, or hardened grease. This can cause inconsistent lever feel and sudden stiffness.
Air in the Hydraulic System
If the system draws air due to low oil or a loose fitting, hydraulic assist becomes inconsistent. Air pockets can cause sudden stiffness followed by normal operation once the air clears.
Why Low Transmission Oil Causes These Symptoms
Transmission oil in a 955 serves multiple functions:
- Lubricates clutch packs
- Provides hydraulic pressure for steering assist
- Cools internal components
- Ensures smooth clutch engagement
- The pump may cavitate
- Pressure drops intermittently
- Clutches may drag or fail to disengage
- Steering becomes stiff or unpredictable
Field Experiences and Anecdotes
Operators of older Caterpillar machines often share similar stories. One farmer recalled fighting stiff steering for weeks before discovering that a slow leak had drained half the transmission oil. Another mechanic remembered a 955 that steered perfectly in cold weather but became stiff in summer heat due to a partially clogged suction screen.
These stories highlight a common theme: simple fluid issues often masquerade as major mechanical failures.
Caterpillar Company Background
Caterpillar has been a leader in heavy equipment manufacturing for nearly a century. The 955 series played a major role in expanding Caterpillar’s presence in the track loader market. Its success stemmed from:
- A reliable drivetrain
- Strong dealer support
- A global parts network
- Machines designed for decades of service
Practical Recommendations
- Check transmission oil level before assuming mechanical failure.
- Use the correct Caterpillar‑approved transmission fluid.
- Inspect for leaks around seals, hoses, and the torque converter housing.
- Clean or replace internal screens and filters if applicable.
- Lubricate all steering linkages to eliminate mechanical binding.
- Avoid operating the machine with stiff steering to prevent clutch damage.
- Monitor oil condition and change it regularly, especially on machines that sit unused.
Conclusion
Steering stiffness on a Caterpillar 955 is often caused by simple issues rather than major mechanical failures. In the documented case, low transmission oil was the culprit, and refilling the system restored normal steering immediately. Understanding how the steering and transmission systems interact helps operators diagnose problems quickly and avoid unnecessary repairs. With proper maintenance and attention to fluid levels, the 955 remains a reliable and capable machine even decades after its introduction.
