797F Off-Highway Truck Steering System: Troubleshooting PART 1

Steering 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 steering piston pump
• Worn steering metering pump
• Pressure setting of steering check and relief valve
• Worn steering check and relief valve
• Leaking steering check and relief valve
• Spools in the steering control valve that do not shift properly
• Worn steering cylinders
• Improperly charged steering accumulators
• Malfunction of accumulator pressure sensor
• Pressure setting of the pressure and flow compensator valve
• Pressure setting of the steering relief valve

Refer to the following sections before performing the troubleshooting checks:

1. Refer to Troubleshooting, "Machine Preparation for Troubleshooting".

2. Perform a visual inspection. Refer to Troubleshooting, "Visual Inspection".

3. If the problem has not been identified, refer to Troubleshooting, "Operational Checks".

4. If the problem is still undetermined, refer to "Performance Tests" within the following section.

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 piston pump

Probable Cause

• Air in the steering hydraulic circuit
• Loose connection of the oil line on the inlet side of the steering piston pump
• Low oil level in the steering hydraulic oil tank
• Wrong oil viscosity

Problem: Turning the steering wheel requires too much force

Probable Cause

• Open backup relief valve
• Low oil level in the steering hydraulic oil tank
• Low oil pressure in the steering accumulators
• Worn steering piston 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 check and relief valves
• Cold oil
• Kinked signal line
• Leaky signal line
• Bad steering solenoid

Problem: The machine does not turn when the steering wheel is turned

Probable Cause

• Air in system
• Malfunction of the steering check and relief valves
• 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 check and relief valves
• The timing between the gerotor and pin (1) on the steering metering pump is not correct.

Timing of the steering metering pump (1) Pin (2) Drive (3) Timing mark (4) Valley of the gerotor star (A) Reference line (B) Reference line(C) Reference line

Timing mark (3) on drive (2) must fall on the parallel line between any two valleys of the gerotor star (4) .

Note: Reference line (A), reference line (B) and reference line (C) are parallel.

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