924K, 926M, 930K, 930M, 938K, and 938M Wheel Loaders Machine System Pilot Pressure - Check Caterpillar


Pilot Pressure - Check
`
1.1. Specifications
2.1. Introduction
3.1. Required Tools
4.1. Machine Preparation
5.1. Test Procedure

------ WARNING! ------

Personal injury can result from hydraulic oil pressure and hot oil.

Hydraulic oil pressure can remain in the hydraulic system after the engine has been stopped. Serious injury can be caused if this pressure is not released before any service is done on the hydraulic system.

Make sure all of the attachments have been lowered, oil is cool before removing any components or lines. Remove the oil filler cap only when the engine is stopped, and the filler cap is cool enough to touch with your bare hand.


------ WARNING! ------

Sudden movement or accidental starting of the machine can cause personal injury or death to persons on or near the machine.

To prevent personal injury or death, perform the following:

Park the machine on a smooth, level surface.

Lower the work tool to the ground and engage the parking brake.

Stop the engine and remove the key.

Block the wheels and install the steering frame lock.



NOTICE

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, PERJ1017, "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.


Specifications

Table 1
Pilot Pressure for 924, 926, 930, and 938 Wheel Loaders 
3150 ± 350 kPa (457 ± 50 psi) at High Idle 

Introduction

The following test procedure will verify whether the pressure setting for the pilot pressure is within the specified limit. The following adjustment procedure will explain the procedure for adjusting the pilot pressure.

Required Tools



Illustration 1g02571852
Tooling (A) 198-4240 Digital Pressure Indicator Gp

Table 2
Required Tools 
Tool  Item  Qty  Part No  Description 
  198-4240  Digital Pressure Indicator Gp 
A1  198-4234  Digital Indicator 
A2 198-4239  Pressure Sensor Gp
(0 to 41,368 kPa (0 to 6,000 psi)) 
A3 198-4236  Adapter Cable As 

Table 3
Required Tools 
Tool  Item  Qty  Part No  Description 
B1  8S-7630  Stand 

Machine Preparation

  1. Move the machine to a smooth, horizontal location that is away from operating machines and away from personnel.

  2. Place the transmission direction in the NEUTRAL position.

  3. Engage the parking brake. Place wheel blocks in front of the wheels and behind the wheels.

  4. Lower the bucket or the work tool to the ground.

  5. Stop the engine.


    Illustration 2g02703117

  6. Install the steering frame lock.


    Illustration 3g00384713
    Typical example

  7. Start the machine and position the lift arms on tooling (B).

  8. Stop the engine.

  9. Relieve the pressure in the hydraulic system.

    Reference: For more information about relieving the hydraulic pressure, refer to the Service Manual module Testing and Adjusting, "System Pressure - Release" for the machine that is being serviced.

    Reference: For more information about preparing the machine for Testing and Adjusting, refer to the Service Manual module Testing and Adjusting, "Machine Preparation for Testing and Adjusting" for the machine that is being serviced.

Test Procedure


NOTICE

Permit only one operator on the machine. Keep all other personnel away from the machine or in sight of the operator.


  1. Relieve the pressure in the hydraulic system.

    Reference: For more information about relieving the hydraulic pressure, refer to the Service Manual module Testing and Adjusting, "System Pressure - Release" for the machine that is being serviced.



    Illustration 4g02703156
    Front guard

  2. Ensure that the engine start switch is in the OFF position. Remove the front guard in order to access the main control valve.


    Illustration 5g03791248
    Main control valve
    (1) Implement pilot pressure test port
    (2) Implement pump discharge pressure test port

  3. Install tooling (A) to pressure tap (1) on the main control valve.

  4. Start the engine and warm the hydraulic oil to a normal operating temperature of approximately 49 to 65°C (120 to 150°F).

  5. Run the engine at high idle.

  6. Press the implement shutoff switch to activate the implement controls.

  7. Record the pressure indicated on tooling (A). Refer to table 1 for the correct pressure.

  8. If the pressure is correct, turn the engine start switch to the OFF position.

    1. Release the hydraulic pressure. Refer to the Service Manual module Testing and Adjusting, "System Pressure - Release".

    2. Remove the test equipment from the machine. Install the front guard.

    3. Start the engine and remove the lift arms from the tooling (B). Position the work tool on the ground and turn the engine start switch to the OFF position.

If the pressure reading is not within specifications, there are several possible causes:

  • The solenoid valve (implement pilot shutoff) may not be working properly. Refer to Troubleshooting, "Solenoid - Test" for information on testing the implement pilot shutoff solenoid.

  • If pilot pressure is erratic, low, or high, the charge pressure relief valve may not be working properly. The charge pressure relief valve is located in the implement valve.

Reference: For information about replacing the solenoid valve for the hydraulic shutoff, refer to the Service Manual module Disassembly and Assembly, "Main Control Valve - Remove" and Disassembly and Assembly, "Main Control Valve - Install".

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