953D, 963D and 973D Track-Type Loaders Steering Is Harsh Caterpillar

Probable Causes

• Hydraulic oil viscosity is incorrect.

• The hystat pump or the hystat motor has failed.

• Hydraulic oil level is low.

• The hydraulic oil contains a large amount of air.

• Operator control settings may be set incorrect.

• The control lever is not calibrated properly.

• The steering pedal position sensors are not calibrated properly.

• The steering supply flow is partially blocked.

• The pump control is suspect or the control needs adjustment.

Recommended Actions

Note: Care must be taken in order to ensure that fluids are contained during performance of inspection, maintenance, testing, adjusting, and repair of the machine. You must be prepared to collect the fluid with suitable containers before opening any compartment or disassembling any component that contains fluid. Dispose of all fluids according to local regulations.

Hydraulic Oil Viscosity Is Incorrect

Ensure that oil is the correct viscosity for the operating conditions. In order to determine the correct oil viscosity, refer to the Operation and Maintenance Manual, "Lubricant Viscosities and Refill Capacities" for your machine.

The Hystat Pump Or The Hystat Motor Has Failed

Check the case drain flow rate for the hystat motor. Damage to or excessive wear of the seal around the hystat motor output shaft may allow hydraulic oil (case drain) to leak past the shaft seal.

Ensure that the hystat motor is not worn to the point that the steering system cannot maintain the correct pressures. Wear to the hystat motor rotating group may cause excessive internal (case drain) leakage. This condition may cause the hystat motor to operate inefficiently, which results in wider (less sharp) turns, excessive noise while steering, low steering or charge pressures, and hesitation prior to turns.

Show/hide table

Personal injury can result if the machine moves while testing. If the machine begins to move during test, reduce the engine speed immediately and engage the parking brake.

1. Start the engine and run the engine.

   ENSURE THAT THE SERVICE BRAKES ARE FULLY APPLIED THROUGHOUT THIS ENTIRE PROCEDURE.

   Warm the hydraulic oil to 65°± 3°C (150°± 5°F).

2. Stop the engine and disconnect hydraulic hose from the fitting on the manifold of the case drain for the hystat motor.

3. Place the end of the hose in a suitable container with a known volume such as a 5 gal bucket.

4. Install a plug at the fitting on the case drain manifold in the same place that the line for the case drain was attached to the hystat motor.

5. Start the engine and set engine speed to HIGH IDLE (2000 rpm).

6. Move the steering lever to the full LEFT TURN position and hold the lever long enough to determine the case drain flow rate. Repeat this step in the full RIGHT TURN position.

   The motor case drain flow rate in each direction should be between 12 L/min (3 US gpm) and 20 L/min (5 US gpm) in either direction.

   1. If the motor case drain flow rate is no more than 20% of the specification, the motor can attain the speed/pressure specifications.

   2. If the motor case drain flow rate is greater when steering one direction than the other, either a cross port leak (on the pressurized side) is present or the flushing valve is stuck in one position. (A cross port leak can cause the machine to drift from straight travel.)

   3. Replace the motor if the flow rate is more than 20% above this specification. The motor is worn and leaking too much. Retest the system after the motor is replaced.

1. Check The Hystat Motor Output Shaft Seal For Damage Or Wear.

   Damage to or excessive wear of the seal around the hystat motor output shaft can allow hydraulic oil (case drain) to leak past the shaft seal.

   To determine if the shaft seal is leaking, perform the following steps:

   1. Remove the hystat motor from the bore in which the motor is installed and wiggle the shaft to see if there is any movement.

      If the shaft does not wiggle, disconnect and remove the hystat motor from the machine and bench test the motor.

   2. Operate the motor at 425 psi in both directions. Observe the shaft seal during bench test operation and look for signs of leakage. If leakage is observed, replace the shaft seal. Carefully examine the shaft for damage where the seal and shaft contact each other. After repair and assembly, test the motor again and look for leakage at the shaft before reinstalling the motor.

      If the shaft is loose, worn, or failed bearings have allowed the shaft to cause wear to the shaft seal.

   3. Disassemble The Hystat Motor And Inspect For Damage

      If the hystat motor has excessive internal wear or damage, disconnect the hydraulic lines and the electrical harness from the motor and remove the motor from the machine. Disassemble the motor and carefully examine all internal parts (port plates, rotating group, bearings, etc.). Replace any worn or damaged parts as necessary and bench test, or replace the worn/damaged motor with a new motor.

Hydraulic Oil Level Is Low

Check the oil level. Add oil, if necessary. Refer to Operation and Maintenance Manual, "Hydraulic System Oil Level - Check" for the 953D and 963D machines. Refer to Operation and Maintenance Manual, "hydrostatic Transmission and Hydraulic System Oil Level - Check" for the 973D machines.

The Hydraulic Oil Contains A Large Amount Of Air

Examine the hydraulic oil for signs of oil aeration. Aerated oil can appear cloudy if the air is finely spread in the oil. An oil sample and subsequent oil analysis can determine if the oil is aerated or if the oil is contaminated. If oil aeration is found, the source of the aeration must be located and eliminated.

Oil aeration may be caused by a number of factors such as low oil levels in the tanks, cavitation in pumps or cylinders, worn pump components (shaft seals, port plates, pump housing seals), or leaks in the system on the suction side of pumps. Air in the oil can make the oil more spongy, causing a lag in cylinder movement. Air in the oil can cause erratic operation of hydraulic components.

• Check all of the fittings and connections for proper torque on the suction side of pumps or on negative pressure side of other motors and other components

• Check the fluid level sight gauge on the side of the hydraulic oil tank. If the hydraulic oil appears cloudy, check the inside of the hydraulic oil tank to ensure that the suction tube and the return oil tube are both in place and that both are submerged in the oil (return oil splashing or spraying back into the tank can aerate oil)

• Examine implement cylinder rod seals for signs of oil leakage or seeping which may allow air to be drawn in when the rod end of the cylinder is below tank/ambient pressure (such as during bucket FLOAT)

• Loosen oil line connections after each hydraulic component (pressure side) and examine the oil for aeration at each inspection point. If the oil appears aerated as the oil seeps out of the loosened connection, that component may be the source of the aeration. The aeration may also be occurring some place between that component and the prior component that showed no signs of aeration

• Examine the suction hose, the main suction manifold, and all suction lines, fittings, and connections from the suction manifold to the hystat pump, the fan pump, and the implement pump. Look for indications of oil leakage. If oil leaks from these lines or connections when the machine is shut down, the connections will also draw air into the hydraulic oil system during operation. This condition will cause the pumps to soak the air and distribute it to the components in that system/circuit and then return the aerated oil back to the tank

• Ensure that the procedure to purge the air from the hydraulic system was completed correctly.

Repair or replace any suspect components and then retest for the symptom.

Operator Control Settings May Be Set Incorrect

Check the operator profile in the Messenger system. You can adjust the "steering response rate" to provide the optimal control setting to meet your needs.

The Control Lever Is Not Calibrated Properly

Be sure that the control lever position sensor is calibrated properly. Refer to Testing and Adjusting, "Hystat Operator Control Calibrations" for your machine.

The Steering Pedal Position Sensors Are Not Calibrated Properly

Be sure that the steering pedal position sensors are calibrated properly. Refer to Testing and Adjusting, "Hystat Operator Control Calibrations" for your machine.

The Steering Supply Flow Is Partially Blocked

Blockages, kinks, or restrictions in both the supply oil lines and the return oil lines can prevent oil flow to or from the hystat motor and can create unusual noises due to the high pressures involved. The hystat motor cannot turn without oil flow to the pump and from the pump. Check for these conditions on all hydraulic oil hoses, lines, and tubes in the steering system.

The Pump Control Is Suspect Or The Control Needs Adjustment

Refer to Troubleshooting, "Diagnostic Code Procedures" in this manual.

Ensure that a problem with the steering system electrical components are not causing the hystat pump to operate improperly. Check the monitoring system for any fault codes that are related to Steering Position Sensor 1, Steering Position Sensor 2, Steering Position Sensor 3, the solenoid for the Left Steer, or the solenoid for the Right Steer. If the signals from the steering position sensors are incorrect, the ECM may not be commanding the solenoid to energize properly, and/or the ECM may not be commanding the solenoid to de-energize properly. Correct any problems with any or all of these components and then retest for the symptom.

If no fault codes exist for the solenoids for the hystat pump control, the solenoids for the steering control and/or the steering position sensors may require calibration. Refer to Testing and Adjusting, "Calibration" for your machine.