Testing and Adjusting
784C and 785C Off-Highway Truck/Tractors Steering System
Steering System Troubleshooting
When a problem with the steering system is defined, use the following procedure:
1. Perform a visual inspection. Refer to Testing and Adjusting, "Visual Inspection".
2. If the problem has not been identified, do "Operation Checks".
3. If the problem is still undetermined, do "Performance Tests".
This procedure will help to identify the steering hydraulic system problems.
Operation Checks
The front wheels must be on a dry, smooth hard surface and the hydraulic oil in the steering system must be warm.
Start the machine. In first gear, slowly drive the machine while you turn the steering wheel. Drive the machine until the hydraulic oil temperature is approximately 65°C (150°F).
Test the steering system with the engine at high idle. Rotate the steering wheel. Measure the time that is required to turn the front wheels from the full right turn position to the full left turn position and back to the full right turn position. If the time is more than 9.0 seconds, there could be a problem in the steering hydraulic system. If the time is less than 7.0 seconds, there could be a problem in the steering hydraulic system.
Failures in the steering system can be at least one of the following items:
* Broken oil line or a leak in an oil line connection
* Worn hydraulic oil pump
* Pressure setting of the backup relief valve
* Worn steering metering pump
* Pressure setting of steering crossover relief valve
* Leaking steering crossover relief valve
* Worn steering cylinders
* Improperly charged accumulators
* Pressure setting of the pressure and flow compensator valve
Performance Checks
Performance checks of the steering system can be used for the following purposes:
* Diagnosis of poor performance
* Source of oil leakage inside the hydraulic system
Problem: Noisy steering pump
Probable Cause
* Air in the steering hydraulic circuit
* Loose connection of the oil line on the inlet side of the pump
* Low oil level in the steering hydraulic tank
* Wrong oil viscosity
Problem: Too much force is required to turn the steering wheel.
Probable Cause
* Open backup relief valve
* Low oil in the steering hydraulic tank
* Low oil pressure in the accumulator
* Worn pump
* Tight end cover on the steering metering pump
* Interference of components on steering column with shaft
* Improper operation of steering metering pump
* Improper operation of steering crossover relief valve
* Cold oil
* Restriction in the steering linkage
* The solenoid that is located on the steering solenoid and relief valve is bad.
Problem: The machine does not turn when the steering wheel is turned.
Probable Cause
* Air in system
* Malfunction in steering crossover relief valve
* Lack of oil in steering metering pump
* Worn steering metering pump
* Disengaged steering column shaft from steering metering pump
Problem: Erratic steering
Probable Cause
* Air in system
* Worn steering linkage
* Worn cylinder piston
* Loose cylinder piston
* Malfunction of steering crossover relief valve
* Incorrect timing of steering metering pump
For proper assembly of the steering metering pump, refer to System Operation, "Metering Pump (Steering)".
Problem: The machine turns too slowly in both directions.
Probable Cause
* Not enough oil flow from the steering pump
* Malfunction of steering crossover relief valve
* Failed accumulator
Problem: The machine turns too slowly in one direction.
Probable Cause
* Restriction in steering metering pump
* Malfunction of steering crossover relief valve
Problem: The steering wheel does not return to the center position correctly.
Probable Cause
* Tight cover on steering metering pump
* Interference of components on steering column with shaft
* Restriction between spool and sleeve in steering metering pump
* Damaged centering springs in steering metering pump
* Broken centering springs in steering metering pump
Problem: Hot oil temperature
Probable Cause
* The steering pump does not destroke.
* Wrong oil viscosity
* Air in the oil
* Low oil in the steering hydraulic tank
* Low pressure setting on the backup relief valve
* Restriction in the line circuit
* Oil leakage by the solenoid in the steering solenoid and relief valve.
Problem: Low oil pressure
Probable Cause
* Low pressure setting on the pressure and flow compensator valve
* Worn steering pump
* The solenoid that is located on the steering solenoid and relief valve is bad.
Problem: The steering wheel turns freely.
Probable Cause
* The sleeve and the spool in the steering metering pump stick due to foreign material.
* Broken centering springs in the steering metering pump
* Damaged centering springs in the steering metering pump
* Incorrect timing of steering metering pump
For proper assembly of the steering metering pump, refer to System Operation, "Metering Pump (Steering)".
Problem: The steering pump does not destroke.
Probable Cause
* High pressure setting of pressure and flow compensator valve
* Damaged steering pump
Problem: Soft steering
Probable Cause
* Air in the steering hydraulic circuit
* Low oil level in tank
* Nitrogen in the steering hydraulic system from a failed accumulator
