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| Illustration 1 | g00791564 |
The axle differential locks are controlled by solenoid valve (1) that is mounted on solenoid and relief valve group (2). The solenoid valve controls the flow of the oil from the solenoid and relief valve group to the clutches for the axle differential locks when the solenoid is activated.
Refer to Systems Operation, Testing and Adjusting, "Machine Preparation for Troubleshooting" before you perform any testing and adjusting or troubleshooting.
Prior to starting with checks on the axle differentials, use Caterpillar ET in order to diagnose any fault codes that may be present. Refer to Systems Operation, Troubleshooting, Testing and Adjusting, RENR3442, "Power Train Electronic Control System" or Systems Operation, Troubleshooting, Testing and Adjusting, RENR8035, "Power Train Electronic Control System".
Visually inspect the lines to the axle differentials and inspect the components of the control system. Inspect the oil in the system for the transfer gear and the differential locks. Refer to Systems Operation, Testing and Adjusting, "Visual Inspection".
Testing The Oil Supply To The Axle Differentials
The axle differential locks can only be selected if the interaxle differential lock is also selected. Oil to the solenoid valve for the axle differential locks is supplied by the solenoid valve for the interaxle differential lock. Both the solenoid valves are located in the solenoid and relief valve group that is mounted on the transfer gear.
Test the supply pressure to the solenoid and relief valve group. Refer to Systems Operation, Testing and Adjusting, "Interaxle Differential - Test".
Test the operation of the solenoid in the solenoid and relief valve group. Refer to Systems Operation, Testing and Adjusting, "Interaxle Differential - Test".
If oil is being supplied to the solenoid valve, test the solenoid valve for correct operation.
Testing the Solenoid
To test the solenoid valve that controls the axle differentials, test the pressure of the oil supply to the solenoid valve and test the pressure of the oil supply from the solenoid valve to the axle differentials.
The solenoid valve for the axle differentials is located above the oil filter for the transfer gear on the inside of the front frame assembly.
- Disconnect line (3) from the elbow in the front axle and insert 6V-9508 Face Seal Plug into the line.
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| Illustration 2 | g00791640 |
- Disconnect line (4) and insert a suitable adapter and a suitable hose from the 1U-5482 Pressure Adapter Group into the line. Attach the opposite end of the hose assembly to one of the 0 to 3400 kPa (0 to 580 psi) pressure gauges in the 1U-5481 Pressure Gauge Group .
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| Illustration 3 | g00791644 |
- Install the correct hose assembly from the 1U-5482 Pressure Adapter Group on the test point for output transfer gears and differential system. Attach the opposite end of the hose assembly to one of the 0 to 3400 kPa (0 to 580 psi) pressure gauges in the 1U-5481 Pressure Gauge Group .
ReferenceRefer to Testing and Adjusting, "General Information" for the location of the test fitting for the machine that is being tested.
- Start the engine and operate the engine at low idle. Select the interaxle differential lock. Observe the pressure gauges. The gauge that is connected to line (4) should not read a pressure. With the oil at normal operating temperature, the correct pressure must be displayed on the gauge that is connected to the test point. Refer to Systems Operation, Testing and Adjusting, "Power Train Pressures".
- Select the axle differential locks. The pressure that is displayed on the gauge that is connected to the line (4) must rise to the same value as the pressure that is displayed on the gauge that is connected to the test point for output transfer gears and differential system.
If the same pressure is displayed on both gauges, the solenoid valve is functioning correctly.
The solenoid valve is not functioning correctly if a pressure is not displayed on the gauge that is connected to the solenoid valve.
If a pressure rise is not noted, use a tag wire to check that the solenoid coil is energized. If the tag wire is attracted to the solenoid coil, this indicates that the solenoid coil is energized. The problem is in the solenoid valve. The problem could be a bent solenoid stem, a screen that is dirty or plugged, or a spring that is weak or broken.
If the tag wire does not indicate that the solenoid coil is energized, the problem may be in the electrical circuit.
If the solenoid does not appear to function, disconnect the connector for the solenoid valve. Check the resistance of the windings of the coil in the solenoid.
The resistance of the windings in the solenoid should be 32.6Ω ± 1.6Ω.
If the resistance of the solenoid windings is outside the specifications replace the solenoid.
If the resistance of the solenoid windings is within the specifications, the problem may lie with the switch for the axle differential locks or with the wiring harness of the machine.
Testing The Pressure In The Axle Differential Locks
Test the pressures for the individual axle differential locks. Refer to Systems Operation, Testing and Adjusting, "Power Train Pressures".
If the pressure in an individual axle differential lock is observed to be lower than the specification, there may be an internal leak in the axle. Check the level of the oil in the axle. Refer to the Operation and Maintenance Manual. If the level of the oil in the axle is higher than the specification, there may be a leak in the seals on the piston of the axle differential lock or there is a leak in the lines for the axle differential lock that are inside the axle. Repair the seals or repair the damaged line.
If the pressure in an individual axle differential lock is observed to be within the specification, the piston in the axle differential lock clutch may be sticking or there may be damage to the plates and to the disks in the axle differential lock. Inspect the oil in the axle for debris that may indicate damage to the axle differential lock. Refer to Systems Operation, Testing and Adjusting, "Visual Inspection". Debris in the oil may indicate damage to the axle differential. Remove the axle differential and inspect the axle differential for damage. Refer to Disassembly and Assembly, RENR5138, "Differential - Disassemble and Assemble".