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Erratic Drive Motor Power in Compact Excavators
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Overview
Compact excavators like the Bobcat E32R rely on dual drive motors to control track movement. Occasionally, operators encounter erratic power delivery, where one track moves sluggishly or loses power entirely. This issue can often resolve temporarily by manipulating the control lever, but underlying mechanical or hydraulic faults are usually present.
Common Causes
Erratic drive motor power is frequently caused by:
  • Spool shifting issues: Internal hydraulic spool valves may not fully engage, disrupting flow to the drive motor.
  • Worn or damaged motor components: Sungear shafts, rotating groups, bearings, or seals can fail over time, especially in older machines or units with extensive hours.
  • Contaminated or degraded hydraulic fluid: Dirt, moisture, or chemical breakdown reduces hydraulic efficiency and can score motor components.
Diagnosis and Inspection
Mechanics typically start by:
  • Removing hydraulic fittings carefully to avoid losing small components.
  • Inspecting the drive motor assembly, including the sungear shaft and rotating group.
  • Checking for scoring or wear on plungers, swash plates, and lens plates.
  • Confirming the motor type through data plates (e.g., HiDash or Nabtesco) to ensure correct rebuild procedures.
Repair Options
Rebuilding the drive motor can be cost-effective compared to full replacement. Steps include:
  • Replacing worn rotating groups, sungear shafts, bearings, and seals.
  • Polishing or lapping swash plates if minor scoring is present.
  • Verifying planetary gearbox integrity.
  • Ensuring the rebuild is performed by a qualified hydraulic shop with experience in compact excavator motors.
Cost Considerations
New OEM drive motors for machines like the Bobcat E32R can exceed CAD 5,500. Rebuilds often cost less, depending on parts and labor, and can extend the motor’s operational life significantly.
Preventive Maintenance
  • Regularly check and replace hydraulic fluid to avoid contamination.
  • Inspect drive motors for signs of scoring or unusual wear during routine service.
  • Operate the machine within manufacturer-recommended load limits to reduce stress on the motors.
Conclusion
Erratic drive motor power in compact excavators is usually solvable through careful diagnosis and motor rebuilds. Understanding hydraulic components, motor types, and proper maintenance can prevent downtime and extend the life of the equipment. Early attention to minor scoring or wear can save significant repair costs and ensure reliable track performance.
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