Reviving the Hitachi EX100-2: Diagnostics, Mechanics, and Common Pitfalls

[MikePhua]

The Challenge of Aging Excavators
The Hitachi EX100-2, part of the EX Dash-2 series from the early 1990s, remains a widely respected 10-ton class machine. Built for reliability, with mechanical simplicity and robust hydraulic design, it still finds use on job sites and private land projects. However, as these machines age past three decades, finding qualified mechanics, especially in areas like Knoxville, Tennessee, becomes a real challenge.
Owners of these machines often face a mix of mechanical degradation, lack of documentation, and shrinking parts availability. The situation is further complicated when machines are purchased second-hand without clear service histories or proper inspection.
Typical Problems in the EX100-2
Over the years, common issues have emerged across multiple owners of the EX100-2. These include:

• Intermittent travel motor engagement
  
• Engine hard starts or no-starts when warm
  
• Weak hydraulic performance, especially under load
  
• Failure of the electronic control module (ECM) or wiring harness deterioration
  
• Hydraulic pump pressure loss due to worn swash plate or compensator valve
  
• Cloudy or milky hydraulic fluid due to condensation or contamination
  

A particular concern with these models is their hybrid control system: a combination of early electronic controls with mechanically actuated pumps. When electrical gremlins appear—especially with sensors and solenoids—troubleshooting becomes both time-consuming and dependent on machine-specific knowledge.
Locating Qualified Mechanics
In regions like East Tennessee, owners may find it difficult to locate mechanics who are both familiar with older Japanese-built machines and willing to work on site. Unlike newer models with CAN bus diagnostics, the EX100-2 often requires:

• Manual pressure testing on multiple ports
  
• Disassembly of hydraulic valve bodies
  
• Tracing and replacing brittle wiring harnesses
  
• Direct inspection of shuttle valves and load-sensing systems
  

Many mechanics with this skill set are either retired or focused on large fleet contracts. Owners often rely on referrals from independent contractors, agricultural repair techs, or mobile heavy equipment mechanics with experience across brands like Komatsu, Kobelco, and older CAT models.
What to Look for in a Mechanic
When hiring someone to diagnose or service an EX100-2, owners should prioritize:

• Experience with 90s-era Japanese excavators
  
• Understanding of pilot control systems and flow dividers
  
• Comfort with hydraulic diagnostics without relying on digital tools
  
• Access to pressure gauges, flow meters, and manual bleed kits
  
• Ability to source or fabricate obsolete fittings and seals
  

Some successful owners have even brought in mechanics from neighboring states who specialize in older imports, coordinating diagnostics, and part shipments in advance.
Stories from the Field
In one case, a landowner near Oak Ridge had an EX100-2 that would lift its boom but refused to swing or travel. After weeks of guessing, a mechanic discovered the travel solenoid coil had shorted, sending incorrect signals to the main valve. Replacement parts were unavailable, but the tech repurposed a coil from an older Deere backhoe after confirming matching specs—reviving the machine at a fraction of dealership cost.
Another story involved a similar machine that had weak hydraulics despite good pressure at idle. The issue? A broken internal spring in the pump’s pressure compensator. The fix involved pulling the pump, something only attempted by a veteran mechanic who knew to inspect the spring-loaded spool even though it wasn’t listed in the basic parts diagram.
Spare Parts and Alternatives
As Hitachi transitions older models out of official support, parts must often be sourced through:

• Aftermarket suppliers and cross-brand compatibility catalogs
  
• Salvage yards specializing in Asian construction machinery
  
• Online communities and machine rebuilders
  
• Custom hydraulic shops capable of rebuilding or re-sealing pump assemblies
  

It’s not uncommon for owners to carry spare hoses, sensors, and filters on-site to reduce downtime. Some have even 3D-printed bracket mounts and replaced factory gauges with universal electronic units.
Long-Term Maintenance Strategy
To extend the life of an EX100-2, the following preventive steps are recommended:

• Replace all main electrical connectors with sealed weatherproof units
  
• Flush the hydraulic system annually and test oil for metal content
  
• Install inline pressure monitoring points for real-time readings
  
• Keep detailed service logs, even retroactively, to aid future diagnosis
  
• Train operators to detect small signs of control lag or vibration anomalies
  

These machines, if properly maintained, can still run productively. Their value lies in simplicity and strength—when paired with a knowledgeable hand.
Conclusion
The Hitachi EX100-2 remains a capable and respected excavator, especially for owner-operators and small contractors. However, keeping one running smoothly requires more than just general mechanical know-how—it demands experience, patience, and creative problem-solving. For those willing to invest in that effort, the reward is a machine that delivers big performance without modern digital fragility. The key lies in finding the right mechanic, nurturing the machine like an antique instrument, and being ready to think outside the parts catalog.