Issues with a Bobcat T190 Hydrostatic Pump

Machine: Bobcat T190 Compact Track Loader

Part Involved: Sundstrand hydrostatic pump

Symptoms: Needed full throttle just to get the final drive to turn

Diagnosis: Indicative of a loss of pressure.

Investigating the Hydrostatic Pump

Lines and connections were all good, and there were no apparent issues with the final drive. The customer sent in their hydrostatic pump for evaluation and potential repair. Cleaning was followed by disassembly and inspection.

The inspection turned up a few issues, the first of which involved damaged piston shoes with grooves and divots. However, while this type of damage is serious, it was not believed to be responsible for the loss of pressure that was causing the main problem.

Both the poppet and the seat of the relief valves were inspected. Further investigation revealed that the real problem was the relief valves. The relief valves (there are four in the pump) were popping where they shouldn’t be popping, but also jammed where they shouldn’t be. They became the main suspect in what was causing the loss of pressure in the hydrostatic pump.

The pump itself only required repairs, and did not need to be replaced. The hydrostatic pump required a new seal kit, a set of piston shoes, and a relief valve assembly.

Conclusion

The Sundstrand hydrostatic pump was not providing the required pressure because of damaged (and malfunctioning) relief values. The required repairs were made and the pump was sent back to its owner.

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