953C Track-Type Loader Caterpillar

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The power train/hydrostatic transmission and the hydraulic system on this machine use the hydraulic tank as a common sump. When the oil in the power train/hydrostatic transmission and hydraulic system gets hot, it causes the air to expand and build up pressure in the hydraulic tank. Pressure can remain in the hydraulic 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/hydrostatic transmission or the hydraulic system. To prevent possible injury, remove the cap from the oil filler tube before any fitting, hose, or component in the power train/hydrostatic transmission or hydraulic system 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 and Instrument Checks and verify the symptom.

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 or instrument tests be performed.

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

The list cannot give all possible problems and 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 hydrostatic transmission, remember that correct oil flow, temperature, and pressure are necessary for correct operation.

Pump output flow is a function of engine speed. Oil pressure is caused by resistance to the flow of oil. 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 a few basic rules are followed:

1. The performance of the system decreases very fast if the level and viscosity of the oil in the transmission 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 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 control lever is placed into the HIGH IDLE detent position.

   2. The performance of the hydrostatic transmission will be affected if the throttle lever position switch for the governor lever position is not activated. This condition will also interfere with troubleshooting.

      Reference: See Systems Operation/Testing and Adjusting, "Troubleshhooting" for the Calibration Chart for additional information.

3. It is possible for the engine to run at a speed lower than HIGH IDLE, even though the governor control lever is in HIGH IDLE.

   1. The low speed could be caused by a linkage problem, quality of the fuel, condition of the fuel filters, and/or air in the fuel system.

   2. Complaints of low power in the hydrostatic transmission can many times be traced to 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.