Diagnosing Hydraulic Failure on the Dynapac CA152 Roller

[MikePhua]

Summary
When a Dynapac CA152 roller suddenly loses travel, vibration, and steering simultaneously, the root cause is likely a failure in the hydraulic power transmission system—most commonly a broken pump coupler or a loss of drive to the hydraulic pump shaft. Despite separate hydraulic circuits, all functions depend on the pump being mechanically driven.
Dynapac CA152 Background and Design
The Dynapac CA152 is a single-drum vibratory soil compactor designed for medium-duty compaction tasks in road construction, site preparation, and utility trench backfill. Manufactured by Dynapac, a Swedish company founded in 1934 and now part of the Fayat Group, the CA152 is part of the CA series known for reliability, operator comfort, and efficient compaction performance.
The CA152 features a hydrostatic drive system, vibration module, and articulated steering—all powered by hydraulic circuits fed from a central hydraulic pump. The engine drives the pump via a coupler or shaft, and any failure in this mechanical link can disable all hydraulic functions.
Key Terminology and System Overview

• Hydraulic Pump Coupler: A mechanical link between the engine and hydraulic pump, often made of rubber or composite material. If it shears or fails, the pump stops rotating.
  
• Hydrostatic Drive: A closed-loop hydraulic system that powers the drum and rear wheels for travel.
  
• Vibration Circuit: A separate hydraulic loop that drives the eccentric weights in the drum.
  
• Steering Circuit: Typically a low-pressure hydraulic system controlling the articulation joint.
  
• Charge Pressure: The base pressure that feeds the hydrostatic loop; loss of charge pressure can disable travel.
  

Failure Symptoms and Diagnostic Path
In the reported case, the roller lost all motion, vibration, and steering simultaneously, while the engine continued to run and the hydraulic oil level remained normal. This points to a mechanical failure between the engine and pump, rather than an internal hydraulic issue.
Recommended diagnostic steps:

• Inspect the pump coupler by removing the pump cover and checking for rotation while the engine runs.
  
• Check for broken splines or sheared rubber elements in the coupler.
  
• Verify pump shaft rotation visually or with a stethoscope to detect vibration.
  
• Test charge pressure using a gauge at the charge port—if zero, the pump is not rotating.
  
• Inspect drive belts or gear couplings if the pump is belt-driven.
  

Field Anecdotes and Practical Advice
A technician in Alberta reported a similar failure on a CA250D roller, where the coupler had sheared cleanly due to age and vibration. The machine showed no hydraulic response, and the replacement coupler restored full function. Another operator in Texas found that a loose set screw on the pump shaft allowed slippage under load, causing intermittent loss of travel and vibration.
In some cases, the coupler may fail silently, with no debris visible. A simple test is to mark the pump shaft and observe whether it rotates during engine operation. If not, the coupler is the likely culprit.
Preventive Measures and Recommendations

• Replace pump couplers every 3,000–4,000 hours or at signs of wear.
  
• Use OEM couplers with correct durometer rating to avoid premature failure.
  
• Inspect coupler alignment during engine or pump replacement.
  
• Monitor hydraulic charge pressure regularly to detect early signs of pump disengagement.
  
• Keep spare couplers on hand for remote job sites.
  

Conclusion
The Dynapac CA152 roller’s simultaneous loss of travel, vibration, and steering is a classic symptom of pump drive failure. Although the hydraulic circuits are separate, they all depend on the pump being mechanically driven. By inspecting the coupler and verifying pump rotation, operators can quickly diagnose and resolve the issue—restoring productivity and avoiding unnecessary downtime.