Removing Boom Pins and Bushings on the Hitachi ZX75UR

[MikePhua]

The ZX75UR and Its Compact Excavator Design
The Hitachi ZX75UR is a short-tail swing compact excavator designed for urban and confined job sites. With an operating weight around 17,000 lbs and a dig depth exceeding 15 feet, it balances power and maneuverability. Hitachi, a pioneer in hydraulic excavator technology since the 1960s, developed the ZX series to meet Tier 4 emissions standards while improving fuel efficiency and operator comfort.
The boom-to-arm joint on the ZX75UR uses hardened steel pins and bronze or composite bushings to allow smooth articulation under high load. Over time, these components wear due to friction, contamination, and lack of lubrication. When movement becomes sloppy or noisy, replacement is necessary to restore precision and prevent structural damage.
Symptoms of Pin and Bushing Wear
Operators typically notice:

• Excessive side-to-side play at the boom-arm joint
  
• Audible knocking during digging or travel
  
• Hydraulic drift when holding a load
  
• Uneven wear on bucket teeth due to misalignment
  
• Grease extrusion or dry spots around the joint
  

In one case from Queensland, a contractor reported that his ZX75UR’s boom would shift laterally during trenching. Inspection revealed over 3 mm of play in the main pin and oval wear in the bushing bore.
Preparation and Safety Before Removal
Removing boom pins and bushings requires planning, safety precautions, and the right tools. The joint is under residual hydraulic pressure and may be loaded with tension from the boom’s weight.
Preparation steps:

• Park machine on level ground and lower boom fully
  
• Disconnect battery and relieve hydraulic pressure
  
• Support boom with cribbing or a rated lifting device
  
• Clean joint area to remove dirt and grease
  
• Mark pin orientation and bushing depth for reference
  

In a fleet in Ontario, a technician used a 10-ton bottle jack and hardwood cribbing to stabilize the boom before pin removal. This prevented sudden movement and allowed precise alignment during reassembly.
Pin Removal Techniques and Challenges
Boom pins are typically retained by:

• Bolt-on flanges or keeper plates
  
• Snap rings or circlips
  
• Press-fit with interference tolerance
  

Removal methods:

• Use a hydraulic press or portable ram to push the pin
  
• Apply penetrating oil and heat to loosen seized pins
  
• Tap gently with brass drift to avoid mushrooming
  
• Rotate pin during extraction to reduce friction
  

Common challenges:

• Pins seized due to rust or lack of grease
  
• Keeper bolts sheared or corroded
  
• Misalignment causing binding
  

In one case from Texas, a contractor used a 20-ton porta-power and heat blanket to remove a seized pin. After 90 minutes of gradual pressure and rotation, the pin broke free without damaging the bore.
Bushing Extraction and Installation
Bushings are press-fit into the boom or arm bore. They may be split-type or solid, depending on model and aftermarket source.
Extraction steps:

• Use a bushing driver or blind puller
  
• Apply heat to bore and freeze bushing to shrink fit
  
• Avoid chiseling or hammering, which can damage bore
  

Installation tips:

• Clean bore and inspect for scoring or ovality
  
• Use anti-seize or light grease on outer surface
  
• Align grease hole with zerk fitting
  
• Press evenly using arbor press or hydraulic tool
  

A technician in British Columbia used dry ice to shrink a solid bronze bushing before installation. The bushing slid in smoothly and expanded to a tight fit as it warmed.
Greasing and Break-In Procedure
After reassembly, proper lubrication is critical. Use high-pressure moly grease rated for pin joints. Grease until fresh product extrudes from both ends of the bushing.
Break-in steps:

• Operate boom slowly for first hour
  
• Recheck pin alignment and torque on keeper bolts
  
• Monitor for noise or binding
  
• Regrease after 10 hours of operation
  

In a municipal fleet in Maine, a ZX75UR was re-bushed and showed improved control and reduced hydraulic noise after break-in. The operator noted smoother bucket transitions and better grading precision.
Preventive Maintenance and Longevity
To extend pin and bushing life:

• Grease daily during active use
  
• Avoid side loading or twisting the boom
  
• Inspect for play monthly
  
• Replace worn seals or zerk fittings
  
• Use OEM or high-grade aftermarket parts
  

Some operators install grease relief valves to prevent overpressure and seal blowout. Others retrofit bushings with graphite inserts for dry operation in dusty environments.
Conclusion
Removing and replacing boom pins and bushings on the Hitachi ZX75UR is a precision task that restores control, reduces wear, and extends machine life. With proper tools, alignment, and lubrication, operators can maintain tight tolerances and avoid costly downtime. Whether trenching in tight alleys or grading near foundations, a well-maintained boom joint ensures the ZX75UR performs with accuracy and confidence.