Oil Recommendations for the Hydraulic Steering System for Specific Off-Highway Trucks{4300, 431F, 5095} Caterpillar

Off-Highway Truck/Tractor:

785C (S/N: 1HW1-UP; APX1-UP; 5AZ1-UP)

Introduction

ReferenceTesting and Adjusting, SENR1492, "784C and 785C Off-Highway Truck/Tractor Steering System", "Relief Valve (Steering) - Test and Adjust"

The problem that is identified below does not have a known permanent solution. Until a permanent solution is known, use the solution that is identified below.

Problem

Some failures of the 190-2279 Piston Pump Gp are caused by excessive case pressure. There are several causes to the excessive case pressure.

• A high operating temperature in the steering circuit

• Inadequate oil viscosity

• Contamination in the steering system

Low oil viscosity causes several problems.

• High case pressure

• A loss of system pressure

• A loss of pump efficiency

The result of all of the problems is a pump failure.

Solution

Use the following recommendations in order to improve the performance of the steering pump.

1. Use a specific oil for high ambient temperatures or extreme temperature variations. A environment with a high ambient temperature is a temperature that is above 30 °C (86 °F). An extreme temperature is an environment that has changes in temperature in the range from −15 °C (5 °F) to 50 °C (122 °F). If you operate a truck in either environment, use the 3E-9712 Engine Oil that is a SAE15W40 engine oil in the tank for the steering system instead of the following oils: SAE30, SAE10W and SAE10W30

2. Maintain oil cleanliness. Test oil cleanliness by scheduled oil sampling that meets the ISO 18/15 requirements. Use a filter cart as part of the preventive maintenance program.

3. Clean up the entire hydraulic system after a pump failure. Flush the steering lines. Flush the tank for the steering system. Flush all of the components in the steering system. Replace the oil filter for the steering system. Replace the hydraulic oil in the steering system. Use a filter cart in order to meet the oil cleanliness of the ISO 18/15 requirements.

4. Refer to the above reference. Verify that the setting for the 6E-6298 Solenoid and Relief Valve Gp is correct. The setting for the solenoid and relief valve group is 207 bar (3000 psi).

5. Before you start the truck, fill the pump case with oil. Release any trapped air from the pump inlet after you fill the pump case.