Troubleshooting Drive Lag and Auxiliary Pressure Loss on the ASV RC85

[MikePhua]

ASV RC85 Background and Market Legacy
The ASV RC85 is a mid-2000s compact track loader developed by ASV Inc., a Minnesota-based manufacturer known for pioneering rubber track undercarriages and suspended track systems. ASV (All Season Vehicles) gained traction in forestry, snow removal, and landscaping sectors due to its machines’ low ground pressure and terrain adaptability. The RC85, equipped with a Perkins 1104C-E44T diesel engine and pilot-controlled hydraulics, was designed for high-flow attachments and demanding work environments.
ASV was later acquired by Terex and eventually became part of Yanmar’s compact equipment division. Despite corporate transitions, the RC85 remains a respected model among operators, with thousands still in use across North America.
Terminology Annotation

• Pilot Control: A low-pressure hydraulic signal system used to actuate main hydraulic valves via joystick input.
  
• Logic Block: A hydraulic control module located beneath the joystick, responsible for interpreting pilot signals and directing flow.
  
• Load Check Valve: A valve that prevents hydraulic fluid from flowing backward through a circuit, maintaining pressure when the control is neutral.
  
• Relief Cartridge: A pressure-limiting valve that opens when system pressure exceeds a set threshold, protecting components from damage.
  

Drive Control Lag and Resolver Block Issues
One recurring issue with the RC85 is sluggish directional response—particularly when transitioning between forward and reverse or executing tight turns. Operators report a delay between joystick input and machine movement, which can compromise precision in confined spaces.
This lag is often attributed to:

• Low pilot pressure at the joystick logic block
  
• Contaminated pilot lines restricting signal flow
  
• Worn joystick internals or proportional solenoids
  
• Faulty resolver block (also referred to as a logic block) beneath the joystick
  

In one case, replacing the logic block resolved the issue entirely. However, another machine required a full joystick replacement, as the internal wear had compromised signal integrity. Rexroth manufactures the joystick assemblies, but replacements must be sourced through ASV due to proprietary fittings and calibration requirements.
Recommended steps:

• Verify pilot pressure at the joystick base (should exceed 400 psi)
  
• Flush pilot lines to remove debris or air pockets
  
• Inspect joystick centering and switch wear
  
• Replace logic block or joystick if pilot pressure is confirmed and lag persists
  

Auxiliary Hydraulic Circuit Pressure Loss
Another common problem involves the auxiliary low-flow circuit failing to hold pressure. Operators using grapple buckets report that the arms open normally but begin to drift downward within seconds, even without load. This behavior suggests internal leakage or control valve malfunction.
Initial diagnostics should include:

• Testing pressure at the quick disconnect (QD) fitting using a 3000 psi gauge
  
• Observing pressure decay after releasing the momentary switch
  
• Swapping relief cartridges between circuits to isolate the fault
  
• Inspecting the push-to-drain valve for backflow to tank
  

In one instance, replacing the relief cartridge had no effect. The grapple was tested on another machine and performed normally, confirming the issue was within the RC85’s hydraulic system. Further investigation revealed that the solenoid valve controlling the auxiliary circuit (SV5) may have worn internal steels, causing drift. Swapping SV5 with SV4 (which controls high-flow) helped isolate the fault.
Recommendations for Resolving Pressure Loss

• Replace SV5 solenoid if pressure drops immediately after switch release
  
• Inspect and cap the case drain line to eliminate backflow from the push-to-drain valve
  
• Confirm that load check valves are present and functioning in the auxiliary circuit
  
• Test grapple cylinders by trapping oil and observing drift over time
  

If the grapple remains raised for days when disconnected, piston seals are likely intact, and the issue lies in the control side.
Engine Reliability and Maintenance Practices
The RC85’s Perkins 1104C engine has a mixed reputation. While generally reliable, some units experience injector wear around 2400–2800 hours. One operator replaced injectors and the injection pump on an RC100 at 2800 hours and on an RC85 at 2400 hours.
To extend engine life:

• Replace fuel, oil, and hydraulic filters every 250 hours (not the factory-recommended 500)
  
• Clean radiator and cooling pans regularly to prevent overheating
  
• Maintain coolant levels and inspect for leaks
  
• Record engine serial number for future parts sourcing
  

Field Anecdotes and Practical Advice
In Tennessee, a technician emphasized the importance of removing belly pans every 250 hours to wash out debris and prevent hydraulic overheating. In Maine, an operator discovered that joystick switch wear caused auxiliary solenoids to drift, leading to pressure loss. Replacing the switch restored normal function.
In Canada, a field mechanic diagnosed drive lag by checking charge pressure near the filters (625–700 psi) and at the HST pump (400–450 psi). Low readings confirmed the need for pump service.
Conclusion
The ASV RC85 remains a capable compact track loader, but age-related hydraulic and electrical issues can affect performance. Drive lag is often linked to pilot pressure and joystick wear, while auxiliary pressure loss typically stems from solenoid valve drift or missing load check valves. With structured diagnostics, targeted component replacement, and proactive maintenance, operators can restore full functionality and extend the machine’s service life. The RC85’s modular design and parts availability make it a viable candidate for long-term use, especially in mixed-attachment environments.