973C Track-Type Loader Power Train Caterpillar

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When the oil in the power train gets hot, it causes the air to expand and build up pressure in the power train oil tank. Pressure can remain in the power train oil tank after the engine and pumps are stopped. Personal injury can occur if pressure is not released before any service is performed on the power train. To prevent possible injury, remove the cap from the oil filler tube before any fitting, hose, or component in the power train is loosened, tightened, removed, and/or adjusted. The cap must be replaced when the tests and/or the adjustments are completed. The bucket and the other attachments must always be flat on the ground before service is performed. When it is necessary for an attachment to be raised while tests and/or adjustments are being performed, be sure the correct supports are in place. In the case of the bucket, it must be in the full DUMP position. Move the machine to a location away from the travel of other machines. Wear the seat belt, and be sure that other personnel are not near the machine when the engine is running and tests or adjustments are being performed.

Procedure

When you are defining a power train problem or a hydrostatic transmission problem, use the following procedure.

First, perform Visual Checks. Next, perform the Operation Checks and verify the symptom.

Lastly, perform the Instrument Tests if the cause of the problem has not been found.

Once the problem is defined, proceed to Troubleshooting.

Since there may be more than one cause for a particular problem, the Troubleshooting section may suggest specific instructions. The Troubleshooting section may also suggest the performance of instrument tests.

These inspections and these tests aid in determining the most probable cause.

The list cannot give all possible problems and all possible corrections. The service personnel must find the problem and the source. Then, the service personnel must make the necessary repairs.

During the diagnosis of a problem in the power train or in the hydrostatic transmission, remember that correct oil flow, correct temperature, and correct pressure are necessary for proper operation.

The pumps create oil flow. Oil pressure is caused by resistance to the oil flow. Oil sump temperature must be a minimum of 52.0 °C (125.6 °F) during diagnosis.

When more checks are necessary, use the appropriate hydraulic gauges or the 131-5051 DataView Group .

Finding the solution to a problem can be made easier if the following information is known:

1. The performance of the system decreases rapidly if the level of the oil in the hydraulic tank is not within specifications. Also, the performance of the system decreases rapidly if the viscosity of the oil in the hydraulic system is not in accordance with specifications.

   1. If the oil level is too low, the unit can malfunction completely.

   2. Oil that is too viscous can cause the filter bypass valve to open. When the filter bypass valve opens, oil is sent back to the sump. This causes a loss in machine speed and a loss in performance.

   Note: There is a filter bypass valve on the inlet side of the filter. The valve opens whenever the pressure difference across the oil filter reaches 345 kPa (50 psi).

   3. Oil that flows through the filter bypass valve is not sent through the transmission.

2. There is a direct relationship between engine speed and the performance of the hydrostatic transmission.

   1. The engine speed must reach HIGH IDLE when the governor switch is moved to the HIGH IDLE position.

   2. The performance of the hydrostatic transmission will be affected if the engine is not in HIGH IDLE. This condition will also interfere with troubleshooting.

3. It is possible for the engine to run at a speed lower than HIGH IDLE, even though the governor switch is moved to the HIGH IDLE position.

   1. One of the following conditions or a combination of the following conditions could cause the low speed: a fault in the ECM, low quality of the fuel, poor condition of the fuel filters and air in the fuel system.

   2. Complaints of low power in the hydrostatic transmission can often be a result of engine problems.

4. Other systems on the machine can cause a decrease in the performance of the drive system.

   1. Incorrect track adjustment can cause the machine to move slowly.

   2. Holding an implement in the engaged position can cause the machine to run slowly. This occurs if the relief valve is already open.