2006 Komatsu WB150 Pump Problems

[MikePhua]

Overview
The Komatsu WB150 is a compact backhoe-loader produced around the turn of the century and updated in the WB150-2N series. It sits in the 7.5–8.0 tonne class, typically powered by a turbocharged four-cylinder Komatsu diesel producing roughly 85–95 horsepower depending on variant, with loader breakout forces and backhoe dig depths aimed at light-to-medium construction and municipal work. These machines commonly accumulate thousands of hours on rental fleets and contractor yards; the example at the center of this story had about 4,500 hours on the clock when symptoms appeared. Komatsu Ltd., founded in 1921, is one of the world’s largest makers of construction equipment and the WB150 represents their small-to-mid backhoe offering used globally for decades.
Symptoms Observed
The owner reported a loud, metallic “chattering” noise from the hydraulic system under work conditions. The noise was most noticeable when the hydraulic pump was asked to deliver flow — a high-pitched, irregular chatter rather than a steady mechanical whine. Because hydraulic pump noise often signals internal wear, the immediate suspicion was that the main hydraulic pump was failing; the owner also discovered that new OEM pump quotes were expensive and reman options were either scarce or priced high.
Common Causes of Pump Chatter

• Air entrainment in the hydraulic suction line or feeder hose. Small leaks or a cracked suction hose let air into the system; trapped air creates cavitation and the characteristic chattering or noisy, erratic pump behavior.
  
• Suction restriction from a clogged inlet or collapsed hose under vacuum. A pump trying to draw through a partial restriction will starve and cavitate.
  
• Internal pump wear—worn vanes, pistons, or cam surfaces can produce noise and loss of pressure. This is a true pump failure and requires rebuilding or replacement.
  
• Incorrect fluid level or wrong viscosity. Too low an oil level or a fluid that is too thin for the operating temperature reduces suction head and can increase cavitation.
  
• Loose mounting or failing ancillary hardware (brackets, couplings, or dampers) creating transmitted noise that can be mistaken for pump failure.
  

Step-by-Step Diagnostic Approach

1. Listen and Localize — Use a stethoscope or hose to localize the noise. Differentiate between pump-body noise versus vibration from mounting points.
   
2. Check Fluid and Fill — Verify reservoir level and fluid condition. Note contamination, foaming, or an unusually low oil level. Record reservoir temperature and ambient temperature as supporting data.
   
3. Inspect Suction and Feeder Lines — Visually and manually examine the full length of the suction hose and fittings. Check for hairline cracks, soft spots, or collapsed sections; squeeze the hose at operating points to feel for vacuum collapse.
   
4. Pressure and Vacuum Tests — Fit gauges: suction vacuum gauge at pump inlet and pressure gauge at pump outlet. Typical acceptable vacuum at the pump inlet under load should be low (a few inches of Hg depending on pump location). High inlet vacuum or fluctuating vacuum indicates suction restriction or air ingress.
   
5. Air Leak Test — With the pump isolated and system off, pressurize the suction side slightly (where design permits) or submerge suspected fittings in water to spot air bubbles during slow cranking/priming.
   
6. Bench Test if Needed — If electrical/mechanical checks point to the pump, remove and bench-test the pump to establish internal leakage or worn components; compare measured flow/pressure to OEM spec.
   
7. Cost Estimate and Compare — Before ordering a new pump, obtain reman quotes, local hydraulic shop rebuild estimates, and dealer pricing. Document serial numbers and pump model to speed quotes.
   

What the Case Revealed
In this particular machine the loud pump chattering turned out not to be a failed pump at all but a small crack in the hydraulic feeder (suction) hose feeding the pump. That tiny crack let air into the low-pressure side of the circuit; even a small amount of air produced cavitation and the loud chattering that mimicked catastrophic pump failure. After the hose was replaced and the system bled and checked for vacuum, the noise disappeared and normal pump performance returned. The owner had initially been quoted several thousand dollars for a new pump, but careful troubleshooting saved the machine from an unnecessary—and expensive—pump exchange.
Practical Recommendations and Solutions

• Always check the suction side first. Suction hoses, fittings and quick connects are the most common and least expensive causes of pump chatter.
  
• Use a vacuum gauge. Measuring inlet vacuum gives quick, objective data. Excessive or fluctuating vacuum almost always points at suction problems.
  
• Record operating hours and maintenance history. A pump with very high hours and known poor oil change history is more likely to have internal wear; conversely, a unit with regular service history is more likely to have a peripheral fault.
  
• Keep spare critical hose lines on hand. A worn feeder hose costs a fraction of a pump and restores reliability quickly in the field. Typical retail cost for a heavy-duty suction hose runs orders of magnitude lower than reman pump pricing.
  
• Consider local pump rebuilding shops. If the pump does need work, a reputable hydraulic shop can often rebuild for a lower price than OEM new—get written flow/pressure guarantees when possible.
  
• When quoted an OEM replacement, ask for comparable remanufactured options and core credit details. That can reduce cost significantly if the damaged part is returned.
  
• After repair, carry out data checks. Compare outlet pressure, flow, reservoir vacuum, and system temperature before and after repair to document success and spot lingering issues.
  

Maintenance and Preventive Measures

• Inspect suction hoses and clamps at each service interval; look for blistering, oil-soaking or abrasion marks.
  
• Maintain correct fluid type and scheduled oil changes to prevent varnish and slugging that can damage pumps.
  
• Install a debris or inlet strainer and keep it clean; a blocked strainer can produce inlet starvation and pump damage.
  
• Fit hose clamps with torque specs and re-check clamp tightness after initial run-in hours.
  
• Train operators to watch for changes in sound and to tag machines for inspection at the first odd noise.
  

Troubleshooting Checklist (quick list)

• Verify hydraulic oil level and quality.
  
• Listen with stethoscope to localize noise.
  
• Inspect suction hose, fittings, and reservoir breather.
  
• Measure suction vacuum and outlet pressure under load.
  
• Replace suspect hoses and retest before condemning pump.
  
• If pump removed, obtain bench test data and compare to OEM specs.
  

Glossary of Terms

• Cavitation — Formation and collapse of vapor bubbles in a liquid caused by local low pressure; produces noise and accelerates wear.
  
• Suction/Vacuum Side — Low-pressure side of the pump where oil is drawn from the reservoir.
  
• Feeder Hose — The hose between reservoir and pump inlet; critical to maintain integrity under vacuum.
  
• Bench Test — Controlled test of a pump on a workbench to measure flow and pressure independent of machine installation.
  
• Core Credit — Refund applied when a worn component is returned to a vendor/manufacturer as exchange for a rebuilt unit.
  

A Short Field Anecdote
A rental company once scheduled downtime and a full pump replacement for a noisy backhoe that had been in heavy service. A supervisor insisted on a quick suction-side inspection and found only a clamped hose joint that had worked slightly loose during winter cycles. One hose clamp and a few minutes eliminated the noise and saved the shop thousands in parts and lost rental revenue. Those “quick checks” often pay for themselves many times over.
Closing Notes and Data Points

• Example machine hours in the case: ~4,500 hours.
  
• Common WB150 power range: ~85–95 hp; machine weight approximately 7.8–8.0 tonnes.
  
• Dealer new pump quote reported as a multi-thousand dollar figure in the field case; local rebuild or a simple hose replacement can be orders of magnitude cheaper.
  
• Practical takeaway: when hydraulic pumps chatter, validate suction integrity and inlet vacuum before assuming internal pump failure.
  

If you want, I can convert the troubleshooting checklist into a printable one-page PDF you can keep in a tool box, or produce a step-by-step vacuum-gauge test protocol with expected numeric ranges for the WB150 family. Which would help most?