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The Bobcat S185 and Its Hydraulic Legacy
The Bobcat S185 skid-steer loader, introduced in the early 2000s, quickly became one of the most popular models in Bobcat’s compact equipment lineup. Manufactured by Bobcat Company, a division of Doosan Group since 2007, the S185 was designed to balance power, maneuverability, and versatility. With a rated operating capacity of 1,850 pounds and a vertical lift path ideal for loading trucks and pallets, it found widespread use in construction, landscaping, and agriculture. By 2010, Bobcat had sold over 100,000 units of the S-series globally, with the S185 being a top seller in North America and Europe.
Symptoms of Lift Arm Drift
One recurring issue reported by operators is the gradual lowering of the lift arms when the machine is running. This phenomenon, known as hydraulic drift, typically manifests as:
Key Components and Terminology
In Saskatchewan, a contractor reported that his 2004 S185 dropped its arms within 30 seconds of idling. After replacing the spool seals and cleaning the valve block, the issue was resolved. In contrast, a fleet operator in Texas found that replacing the solenoid coil alone did not fix the problem—only after inspecting the stem and replacing the entire valve assembly did the drift stop.
Preventive Measures and Solutions
Lift arm drift in the Bobcat S185 is a manageable issue once the root cause is identified. Most often, it stems from internal leakage in the control valve block rather than the lift cylinders. Through careful diagnosis, seal replacement, and system flushing, operators can restore full functionality and extend the life of their equipment. The S185 remains a workhorse in the compact loader category, and with proper maintenance, its hydraulic system can perform reliably for years to come.
The Bobcat S185 skid-steer loader, introduced in the early 2000s, quickly became one of the most popular models in Bobcat’s compact equipment lineup. Manufactured by Bobcat Company, a division of Doosan Group since 2007, the S185 was designed to balance power, maneuverability, and versatility. With a rated operating capacity of 1,850 pounds and a vertical lift path ideal for loading trucks and pallets, it found widespread use in construction, landscaping, and agriculture. By 2010, Bobcat had sold over 100,000 units of the S-series globally, with the S185 being a top seller in North America and Europe.
Symptoms of Lift Arm Drift
One recurring issue reported by operators is the gradual lowering of the lift arms when the machine is running. This phenomenon, known as hydraulic drift, typically manifests as:
- Arms slowly dropping even when no control input is given.
- Drift halting when the machine is shut off or the seat bar is lifted.
- No drift when the arms are used to lift the machine off the ground.
Key Components and Terminology
- Spool Valve: A sliding valve inside the control block that directs hydraulic fluid to the lift cylinders. Worn or damaged seals here can allow fluid to bypass internally.
- Solenoid Coil and Stem: Electrically actuated components that open or close hydraulic paths. A faulty coil may not fully engage the stem, leading to leakage.
- Spool Lock: A safety mechanism that prevents unintended movement of the loader arms. If malfunctioning, it may allow drift even when the system is idle.
- Internal Leakage in the Control Valve Block: Over time, seals around the spool valve degrade, allowing pressurized fluid to leak past the valve even when it’s in the neutral position. This is the most common cause of lift arm drift in older machines.
- Contaminated Hydraulic Fluid: Dirt or water in the hydraulic system can damage seals and create scoring on valve surfaces. This leads to uneven sealing and fluid bypass.
- Faulty Solenoid or Electrical Signal: If the solenoid coil is weak or the wiring is compromised, the valve may not fully close, allowing fluid to escape slowly.
- Improper Calibration of Linkage or Actuator: Though less common, misaligned mechanical linkages can cause the valve to remain slightly open, especially if the joystick or foot pedal doesn’t return to true neutral.
- Audible Fluid Movement: If you can hear fluid passing through the valve while trying to hold the arms steady, it’s a strong indicator of internal leakage.
- Bench Testing the Valve Block: Removing the control block and applying hydraulic pressure externally can help isolate the leak. If the arms drift during bench testing, the issue lies within the block.
- Cylinder Isolation Test: Disconnect the lift cylinders and cap the lines. If drift persists, the cylinders are not the cause.
In Saskatchewan, a contractor reported that his 2004 S185 dropped its arms within 30 seconds of idling. After replacing the spool seals and cleaning the valve block, the issue was resolved. In contrast, a fleet operator in Texas found that replacing the solenoid coil alone did not fix the problem—only after inspecting the stem and replacing the entire valve assembly did the drift stop.
Preventive Measures and Solutions
- Replace Spool Seals Every 2,000 Hours: This interval aligns with typical wear patterns and helps prevent internal leakage.
- Flush Hydraulic System Annually: Especially in dusty or humid environments, this prevents contamination-related damage.
- Inspect Electrical Connections Quarterly: Loose or corroded terminals can affect solenoid performance.
- Use OEM or High-Quality Aftermarket Parts: Inferior seals and valves may not meet the pressure tolerances required for Bobcat systems.
Lift arm drift in the Bobcat S185 is a manageable issue once the root cause is identified. Most often, it stems from internal leakage in the control valve block rather than the lift cylinders. Through careful diagnosis, seal replacement, and system flushing, operators can restore full functionality and extend the life of their equipment. The S185 remains a workhorse in the compact loader category, and with proper maintenance, its hydraulic system can perform reliably for years to come.
