CYLINDER BLOCK GP 2W4859 - Caterpillar

Hand Metering Unit (HMU) Steering
Personal injury or death can result from machine articulation or movement.Machine frames can move and a person can be crushed.Connect the steering frame lock link between the front and rear frames before working on machine.
Personal injury or death can result from escaping fluid under pressure.Escaping fluid under pressure, even a very small pin-hole size leak, can penetrate body tissue and cause serious injury and possible death. If fluid is injected into your skin, it must be treated immediately by a doctor familiar with this type of injury.Always use a board or cardboard when checking for a leak.
Care must be taken to ensure that fluids are contained during performance of inspection, maintenance, testing, adjusting, and repair of the product. Be prepared to collect the fluid with suitable containers before opening any compartment or disassembling any component containing fluids.Refer to Special Publication, NENG2500, "Dealer Service Tool Catalog" for tools and supplies suitable to collect and contain fluids on Cat products.Dispose of all fluids according to local regulations and mandates.
Performance tests for the steering system can be used for a diagnosis of poor performance. Performance tests can also be used to locate the source of oil leaks inside the hydraulic system.This section provides probable causes to a known problem. Since there may be several probable causes, specific inspections or specific instrument tests may be recommended. These inspections and tests will help to identify the cause that is most probable.Note: Make sure that you use hydraulic oil with the correct viscosity for the ambient temperature and for the operating conditions. To determine the correct oil viscosity, see the reference that follows.Reference: For additional information about the various lubricant viscosities for your machine, refer to the section “Lubricant Viscosities” in the appropriate Operation and Maintenance Manual for your machine.Problem 1: Turning The Steering Wheel Is Difficult
Probable causes:
The oil is cold.
There is a restriction in an oil line of the steering metering pump.
The backup relief valve for the steering system has malfunctioned.
Steering pump pressure is low.
Bolts are too tight for the metering section of the steering metering pump.
There is a leak or blockage in the load sensing line.Problem 2: The Machine Does Not Turn Evenly
Probable causes:
The steering metering pump is sticking.
The margin pressure of the steering pump is set too high.
The steering