Troubleshooting High Flow Hydraulic Issues on the Bobcat T770

[MikePhua]

The Bobcat T770 and Its Hydraulic Capabilities
The Bobcat T770 compact track loader is a high-performance machine designed for demanding applications such as land clearing, mulching, and heavy-duty grading. Introduced as part of Bobcat’s M-series, the T770 features a vertical lift path, a rated operating capacity of 3,475 pounds, and a turbocharged diesel engine producing around 92 horsepower. One of its standout features is the optional high-flow hydraulic system, which delivers up to 36.6 gallons per minute at 3,500 psi—ideal for powering attachments like cold planers, stump grinders, and snow blowers.
Bobcat Company, founded in 1947 in North Dakota, has become a global leader in compact equipment. The T770 remains one of its best-selling models, with thousands of units in operation across North America and Europe.
Terminology Explained

• High-Flow Hydraulics: An enhanced hydraulic circuit that provides greater flow and pressure for demanding attachments.
  
• Solenoid Valve: An electrically controlled valve that directs hydraulic fluid to specific circuits.
  
• Auxiliary Hydraulics: The hydraulic lines and controls used to power external attachments.
  

Common Symptoms of High Flow Failure
Operators encountering high flow issues on the T770 often report:

• High flow light illuminates but no power reaches the attachment
  
• Low or no pressure at the auxiliary couplers
  
• Attachments spin up but stall under load
  
• Audible clicking from solenoids but no fluid movement
  

These symptoms suggest that while the control system is attempting to engage high flow, the hydraulic circuit is not delivering the expected output.
Root Causes and Diagnostic Steps

• Faulty High Flow Solenoid The solenoid responsible for activating the high flow circuit may be stuck, weak, or electrically disconnected. Use a multimeter to verify voltage at the solenoid when the high flow button is pressed.
  
• Contaminated Hydraulic Oil Debris or water in the hydraulic fluid can clog filters or damage valves. Check for milky or dark fluid and replace if necessary.
  
• Clogged Case Drain or Return Line A blocked return path can cause pressure buildup and prevent flow. Inspect hoses and fittings for kinks or restrictions.
  
• Software or Controller Fault The loader’s control module may fail to send the correct signal to the solenoid. A diagnostic scan tool can reveal stored fault codes.
  
• Worn Hydraulic Pump After 4,000–6,000 hours, the main pump may lose efficiency. A flow test can confirm whether the pump is producing rated output.
  

A Story from the Field
In Alberta, a contractor using a T770 for forestry mulching noticed the drum would spin but stall under load. The high flow light activated, but pressure at the couplers was low. After replacing the solenoid and flushing the hydraulic system, the issue persisted. A technician eventually discovered a cracked O-ring inside the high flow valve body, causing internal bypass. Once replaced, the machine returned to full performance.
Recommended Solutions

• Replace high flow solenoid if resistance is outside spec
  
• Flush and refill hydraulic system with ISO 46 premium fluid
  
• Clean or replace hydraulic filters and screens
  
• Inspect couplers for internal damage or wear
  
• Perform a flow and pressure test at the auxiliary ports
  

Preventive Maintenance Tips

• Change hydraulic fluid every 1,000 hours or annually
  
• Replace filters every 500 hours
  
• Inspect solenoid connectors and wiring quarterly
  
• Use only Bobcat-approved attachments to avoid overloading the system
  

Conclusion
High flow hydraulic issues on the Bobcat T770 can stem from electrical faults, fluid contamination, or mechanical wear. By systematically testing solenoids, inspecting fluid condition, and verifying flow output, operators can isolate and resolve the problem. With proper maintenance and diagnostics, the T770 remains a powerful and dependable machine for high-demand applications.