10-27-2025, 09:02 PM
Understanding the Center Joint Function
The center joint, also known as the swivel joint or rotary manifold, is a critical hydraulic component in excavators like the Hitachi EX60URG. It allows hydraulic fluid to pass between the upper structure and the undercarriage while enabling 360-degree rotation. This joint feeds pressure to travel motors, blade circuits, and auxiliary functions. When seals inside the joint fail, hydraulic fluid can leak into the swing bearing compartment or onto the undercarriage, causing grease displacement, pressure loss, and contamination.
The EX60URG, a zero-tail-swing variant of the EX60 series, shares its center joint design with earlier EX60-1 and EX60-2 models. Despite its compact frame, the internal layout remains similar, making seal kits and repair procedures largely interchangeable across these variants.
Terminology Notes
Operators often notice hydraulic fluid pushing grease out of the swing bearing or dripping from the lower car body. If gear oil levels in the swing motor remain stable, the leak likely originates from the center joint. In some cases, fluid may pool inside the swing gear compartment, indicating seal failure at the joint’s lower case.
A slow leak without active machine operation suggests case pressure rather than line pressure—meaning the seals are compromised but not catastrophically failed. However, if fluid loss exceeds one liter every few minutes, immediate repair is necessary to prevent system damage.
Disassembly and Seal Replacement Strategy
Repairing the center joint involves several steps:
Field Experience and Practical Advice
One technician rebuilt his EX120 center joint in eight hours using a $100 seal kit, avoiding a $2,000 shop bill. Another mechanic emphasized that smaller machines like the EX60URG are harder to access due to tighter hose spacing. A third operator discovered that his leak was not from the center joint but from the swing motor seal, which had failed and flooded the bearing compartment.
A common mistake is misdiagnosing the leak source. If fluid appears only on the undercarriage and not on the ground, the swing motor may be the culprit. Conversely, if fluid drips directly beneath the joint, the center joint seals are likely compromised.
Recommendations for Successful Repair
Repairing the center joint on a Hitachi EX60URG is a manageable task with the right preparation and attention to detail. While the compact design poses access challenges, marking hoses, venting the tank, and handling ball bearings carefully can streamline the process. Accurate diagnosis is essential—distinguishing between swing motor and center joint leaks prevents unnecessary disassembly. With a quality seal kit and methodical approach, operators can restore hydraulic integrity and extend the life of their machine.
The center joint, also known as the swivel joint or rotary manifold, is a critical hydraulic component in excavators like the Hitachi EX60URG. It allows hydraulic fluid to pass between the upper structure and the undercarriage while enabling 360-degree rotation. This joint feeds pressure to travel motors, blade circuits, and auxiliary functions. When seals inside the joint fail, hydraulic fluid can leak into the swing bearing compartment or onto the undercarriage, causing grease displacement, pressure loss, and contamination.
The EX60URG, a zero-tail-swing variant of the EX60 series, shares its center joint design with earlier EX60-1 and EX60-2 models. Despite its compact frame, the internal layout remains similar, making seal kits and repair procedures largely interchangeable across these variants.
Terminology Notes
- Center Joint: A hydraulic rotary manifold that transfers fluid between rotating and stationary parts.
- O-Ring: A circular elastomer seal used to prevent fluid leakage between mating surfaces.
- Ball Bearings: Small spherical components that reduce friction and support rotational movement inside the joint.
- Zero Tail Swing: A design where the counterweight does not extend beyond the track width, improving maneuverability in tight spaces.
Operators often notice hydraulic fluid pushing grease out of the swing bearing or dripping from the lower car body. If gear oil levels in the swing motor remain stable, the leak likely originates from the center joint. In some cases, fluid may pool inside the swing gear compartment, indicating seal failure at the joint’s lower case.
A slow leak without active machine operation suggests case pressure rather than line pressure—meaning the seals are compromised but not catastrophically failed. However, if fluid loss exceeds one liter every few minutes, immediate repair is necessary to prevent system damage.
Disassembly and Seal Replacement Strategy
Repairing the center joint involves several steps:
- Vent the hydraulic tank to prevent fluid spray during hose disconnection.
- Label all hoses on the top and bottom of the joint to ensure correct reassembly.
- Remove the joint carefully, noting its orientation and mounting position.
- Separate the joint over a container, as uncaged ball bearings may spill out.
- Replace all internal seals, including the large O-ring between the upper and lower cases.
- Inspect the housing for grooves, which may indicate wear from bearing rotation. Severely grooved housings may be unrepairable.
Field Experience and Practical Advice
One technician rebuilt his EX120 center joint in eight hours using a $100 seal kit, avoiding a $2,000 shop bill. Another mechanic emphasized that smaller machines like the EX60URG are harder to access due to tighter hose spacing. A third operator discovered that his leak was not from the center joint but from the swing motor seal, which had failed and flooded the bearing compartment.
A common mistake is misdiagnosing the leak source. If fluid appears only on the undercarriage and not on the ground, the swing motor may be the culprit. Conversely, if fluid drips directly beneath the joint, the center joint seals are likely compromised.
Recommendations for Successful Repair
- Take reference photos before disassembly to aid reinstallation
- Use a clean workspace to prevent contamination of internal components
- Replace all seals, not just the failed one, to avoid repeat repairs
- Run the machine at low idle after reassembly to purge air from the system
- Monitor hydraulic fluid levels and inspect for leaks during initial operation
Repairing the center joint on a Hitachi EX60URG is a manageable task with the right preparation and attention to detail. While the compact design poses access challenges, marking hoses, venting the tank, and handling ball bearings carefully can streamline the process. Accurate diagnosis is essential—distinguishing between swing motor and center joint leaks prevents unnecessary disassembly. With a quality seal kit and methodical approach, operators can restore hydraulic integrity and extend the life of their machine.
