424B Backhoe Loader Hydraulic and Steering System Caterpillar

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Sudden movement of the machine or release of oil under pressure can cause injury to persons on or near the machine. To prevent possible injury, perform the procedure that follows before testing and adjusting the hydraulic system.

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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.

Note: Put identification marks on all lines, on all hoses, on all wires, and on all tubes for installation purposes. Plug all lines, all hoses, and all tubes to prevent fluid loss and to keep contaminants from entering the system.

Valve Identification

There is a main relief valve in bank valve group. The pressure spool of the compensator valve acts as a main relief for backhoe operation. The pressure spool of the compensator valve limits the system pressure to 24100 to 24900 kPa (3495 to 3611 psi). Main relief valve is set to 23100 to 23900 kPa (3350 to 3466 psi).

Do not increase the pressure compensator valve in an attempt to set the line relief valves that are set above the pump compensator spool setting. The line relief valves are sensitive to flow and the line relief valves cannot be accurately set with the hydraulic pump.

The line relief valves must be removed from the machine. The line relief valves may need to be bench tested if the line relief valves are set above the main relief setting.

Prior to removing the line relief valve, perform the swing test, the test for the implement, and the test for the stabilizer cycle time. Then, perform the margin pressure test, the low-pressure standby test, and the high-pressure stall test. If a function is still suspected, stall that function and listen for the line relief valve to open. If the line relief valve does not open, then the line relief valve is set above the system pressure. Check the line relief valve pressure settings in order to verify that the line relief valves are within the specifications.

Illustration 1	g03616838

This is the location of the backhoe control valve.

Remove the floor plates in order to gain access to the top of the backhoe control valve. Refer to Disassembly and Assembly, "Floor plates - Remove and Install".

Illustration 2	g03591260

This is the location of the loader control valve.

Remove the floor plates in order to gain access to the top of the loader control valve. Refer to Disassembly and Assembly, "Floor plates - Remove and Install".

Mechanically Operated Controls

Two Bank Valve for the Loader Control

Illustration 3	g03589580
(1) Base end line relief valve for the tilt control valve (2) Rod end line relief valve for the tilt control valve (3) Steering priority valve

Six Bank Valve for the Backhoe Control

Illustration 4	g03589581
(1) Head end line relief valve for the stick control (2) Head end line relief valve for the bucket control (3) Right swing circuit line relief valve for the swing control (4) Rod end line relief valve for the boom control (5) Rod end line relief valve for the stick control (6) Rod end line relief valve for the bucket control (7) Left swing circuit line relief valve for the swing control (8) Head end line relief valve for the boom control

Relief Valve Test

1. Use the following steps in order to test or check the appropriate relief valve setting.

2. Lower all of the work tools and the stabilizers to the ground.

3. Stop the engine.

4. Turn the key to the ON position and move all of the control levers to all of the positions to release the system pressure.

5. Turn the key to the OFF position.

6. Remove the line relief valve that will be tested.
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   Illustration 5	g03130837
   (1) Test manifold block (2) Line relief valve (3) Pipe adapter (4) Quick connect coupler (5) Quick connect coupler (6) Hose assembly

7. Secure 1U-5216 Test Manifold Block (1) in a suitable holding device.

8. Install two 030-8370 Pipe Adapter (3) and two 1P-2375 Quick Connect Coupler (4) in 1U-5216 Test Manifold Block (1).

9. Attach two 1P-2376 Quick Connect Coupler (5) to two 8F-0024 Hose As (6).

10. Install line relief valve (2) in 1U-5216 Test Manifold Block (1).

11. Connect two 8F-0024 Hose As (6), two 3B-7722 Pipe Bushing, and 7J-8611 Pipe Elbow to 3S-6224 Electric Hydraulic Pump Gp.

12. Connect 8T-0860 Pressure Gauge to 3S-6224 Electric Hydraulic Pump Gp.

13. Turn the 3S-6224 Electric Hydraulic Pump Gp to the ON position. Check for leaks at the connection.
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    NOTICE
    The 3S-6224 Electric Hydraulic Pump only has a 7.6 L (2 US gal) reservoir. Pump damage may result if the pump is operated with an empty reservoir.

14. Slowly increase the pressure. Record the pressure, when the line relief valve opens. Compare this pressure to Table 2 or 3.

15. Stop the pump.
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    Table 2

    Line Relief Valve Pressure Settings
    Cylinder	Circuit	Setting
    Auxiliary for the Loader	Head end for the Auxiliary Cylinder
    Loader Tilt Circuit for the Single Tilt Machine	Rod end for the Dump Operation	30000 kPa (4351 psi)
    	Head end for the Tilt Back Operation

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    Table 3

    Line Relief Valve Pressure Settings
    Cylinder	Circuit	Setting
    Backhoe Boom	Head end to LOWER	19200 kPa (2785 psi)
    	Rod end to RAISE	27000 kPa (3916 psi)
    Backhoe Swing	Rod end to Swing LEFT	30000 kPa (4351 psi)
    	Rod end to Swing RIGHT
    Backhoe Bucket	Head end of the Bucket Cylinder	27000 kPa (3916 psi)
    	Rod end of the Bucket Cylinder
    Backhoe Stick	Head end for retracing the Stick IN	30000 kPa (4351 psi)
    	Rod end for extending Stick OUT

16. If the line relief valve is within the specification, then go to Step 18. If the line relief valve is not within the specification, then an adjustment is required.
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    Illustration 6	g03132517
    Relief valve (7) Cap (8) Adjusting screw (9) Locknut

    1. Remove cap (7). Loosen locknut (9) and turn adjusting screw (8) clockwise in order to increase pressure. Turn adjusting screw (8) counterclockwise in order to decrease pressure.

    2. Check the oil level in 3S-6224 Electric Hydraulic Pump Gp and refill the oil if it is necessary. Repeat Steps 13, 14, 15, and 16.

17. Tighten locknut (9) to a torque of 20 ± 3 N·m (177 ± 27 lb in).

18. Remove line relief valve (2).

19. Install a new O-ring on line relief valve (2).

20. Install the line relief valve in control valve to a torque of 45 ± 5 N·m (33 ± 4 lb ft).

BOOM LOWER Test

1. Engage the boom lock.

2. Run the engine at the low idle. See Table 4 for the appropriate engine speed.
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   Table 4

   Machine Sales Model	Engine rpm
   424B	1200 rpm

3. Push the boom control lever fully forward in order to activate the BOOM LOWER circuit.

4. Note the pressure reading at pressure tap.

5. Refer to Table 5 for the proper pressure readings at pressure port.
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   Table 5

   Hydraulic Circuit	Pressure
   BOOM LOWER	18800 to 19600 kPa (2727 to 2843 psi)

6. Lower the work tools to the ground. Engage the parking brake and stop the engine.

   Note: By using the gauge, small leakage problems such as a cut seal or a missing seal can be detected.