Diagnosing Steering and Track Power Loss on the Hitachi EX60: Swivel Joint Failures and Hydraulic Clarity

[MikePhua]

Introduction: When Heat and Steering Go Hand in Hand
The Hitachi EX60 excavator is a compact yet capable machine, widely used in utility work, forestry, and small-scale earthmoving. But when steering becomes erratic and track power fades as hydraulic oil heats up, the issue often lies deeper than the pump or joystick—it’s a symptom of internal leakage, most commonly within the center swivel joint. This article explores the diagnostic journey behind such failures, explains the hydraulic architecture of the EX60, and offers actionable repair strategies based on field experience.
Symptoms and Initial Observations
Operators reported the following:

• Machine steers slightly to one side when cold.
  
• After warming up, steering becomes difficult and track power drops significantly.
  
• One track retains slightly more power than the other.
  
• All other hydraulic functions (boom, arm, bucket, swing) operate normally.
  
• Hydraulic oil used was #42 weight, raising concerns about viscosity.
  

These symptoms suggest a localized hydraulic issue affecting the travel circuit, rather than a global pump failure.
Understanding the Hydraulic Architecture of the EX60
The EX60 uses a dual bent-axis axial piston pump system:

• Rear Pump: Feeds LH travel, auxiliary, boom II, arm I, and swing.
  
• Front Pump: Feeds RH travel, bucket, boom I, and arm II.
  

Each travel motor receives high-pressure oil through a rotary manifold (center swivel), which allows fluid transfer between the upper rotating structure and the lower undercarriage without flexible hoses.
Center Swivel Joint: The Hidden Culprit
The center swivel joint is a multi-channel rotary coupling with internal seals and lands. Over time, these seals wear grooves into the chrome-plated center post, allowing high-pressure oil to leak between channels. This leakage:

• Reduces pressure to travel motors.
  
• Causes heat buildup in the manifold.
  
• Leads to asymmetric power delivery between tracks.
  

Operators confirmed that one of the upper hydraulic lines felt significantly hotter than adjacent lines—an indicator of internal leakage.
Field Anecdote: The Rechromed Swivel Fix
One technician had the center post removed and sent to a hydraulic shop for rechroming. The shop replaced all internal seals, polished the lands, and reassembled the unit. Cost: $500–800. Result: full restoration of track power and steering control. This repair is far more economical than replacing pumps or motors unnecessarily.
Hydraulic Line Identification

• Top Small Line: Case drain (low-pressure return)
  
• Top Large Line: Reverse travel
  
• Bottom Large Line: Forward travel
  

Understanding these lines helps isolate flow direction and diagnose pressure loss.
Additional Diagnostic Recommendations

• Check pilot pressure to both travel motors.
  
• Inspect bypass flow on return lines—there should be minimal oil draining back to tank.
  
• Use infrared thermometer to compare line temperatures after 30–60 minutes of operation.
  
• Confirm hydraulic oil viscosity matches manufacturer specs; thinner oil may exacerbate leakage.
  

Suggested Parameters for Inspection

• Hydraulic Oil Viscosity: Use OEM-recommended spec (typically ISO 46 or equivalent)
  
• Swivel Joint Seal Count: 5–7 seals depending on blade configuration
  
• Acceptable Return Flow: Minimal bypass from travel motors
  
• Temperature Differential: >10°C between lines may indicate leakage
  

Preventive Maintenance Tips

• Replace hydraulic oil at recommended intervals; avoid mixing viscosities.
  
• Periodically inspect swivel joint for external leaks or excessive heat.
  
• Monitor track performance symmetry—early signs of internal leakage often appear as steering drift.
  
• Keep a log of hydraulic temperatures and pressures during routine operation.
  

Conclusion: The Swivel Joint Tells the Story
When a Hitachi EX60 begins to steer poorly and lose track power as it warms up, the center swivel joint is often the silent culprit. While pumps and motors may seem like the obvious suspects, internal leakage within the rotary manifold can mimic more serious failures. With proper diagnosis, targeted repair, and attention to hydraulic detail, operators can restore full functionality without unnecessary expense.
Final Advice
Before replacing expensive components, start with the swivel. A few seals and a polished center post may be all that stands between frustration and flawless operation. In hydraulic systems, the smallest leak can have the biggest impact.