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How to Complete an HST Charge Pressure Test on Your Yanmar Tractor

We want to help you complete an HST charge pressure test on your Yanmar tractor.

If you do not feel that you understand these steps, or can perform them safely, consult your tractor dealer or local mechanic. Also always consult your tractor owner’s manual for model-specific information.

The purpose of this test is to make sure that the hydrostatic pump is producing sufficient pressure to operate the hydrostatic motor pump.

Time to get started.


1 Remove the rear right wheel.

  • Make sure to use a suitable lifting device.

  • Make sure to support the rear axle with suitable jack stands.

  • Make sure that the range gear lever is in the N (neutral) position. (SA324/424 only.)

2. To complete this task you will need to purchase the following equipment and tools:

  • Adapter fitting (3/8")

  • Hydraulic pressure gauge

  • Hose with coupler

3. Warm up the hydraulic oil.

  • Start the engine.

  • Operate the hydraulic system to circulate and heat up the hydraulic oil.

  • The hydraulic oil must be heated up to the normal operating temperature of 140 °F (60 °C).

  • Check for oil leaks.

  • Shut off the engine.

IMPORTANT: Avoid damage. Do not overheat the hydraulic oil.

CAUTION: Avoid injury. Escaping fluid under pressure can penetrate the skin causing serious injury.

4. Hydrostatic transmission (HST) charge pressure test.

  • Remove the test port plug from the charge pressure test port (A, Fig.1) in the center plate.

  • Install the following to the charge pressure test port.

- Adapter fitting

- Hydraulic pressure gauge (B, Fig.1)

- Hose with coupler

  • Perform the following procedure.

- Start the engine

- Run the engine at 3200 rpm