143H and 163H Motor Graders All Wheel Drive Caterpillar

This is the procedure for checking the charge pressure. Improper charge pressure will cause the following four problems:

• When the machine is moving, the all wheel drive piston motors will clack too much during engagement.

• The all wheel drive piston motors will not engage.

• The pressure from the all wheel drive piston pump will not increase.

• The all wheel drive system overheats quickly at low operating pressures.

The charge pressure system has two separate sequence valves. The sequence valves determine the charge pressure and the purge pressure for the all wheel drive system. Both the purge pressure sequence valve and the charge pressure sequence valve need to be adjusted in order to obtain the correct system pressure. The all wheel drive gear pump supplies the pressurized oil to the sequence valves.System Operation

Reference: Refer to Troubleshooting, "Flushing and Cooling Control Valve".

Test Step 1. Perform the following test: Machine Preparation for Troubleshooting

Results:

• OK - Proceed to test step 2.

Test Step 2. Perform the following test: Hydraulic Pressure - Release

Results:

• OK - Proceed to test step 3.

Test Step 3.

1. Test the sequence valves for the all wheel drive system.

Reference: Refer to Troubleshooting, "Sequence Valve - Test and Adjust".

Expected Result:

The charge pressure is correct.

Results:

• No - Proceed to test step 4.

• Yes - Proceed to test step 5.

Test Step 4. Perform the following test: Gear Pump (All Wheel Drive) - Test

Results:

• OK - Proceed to test step 6.

• REPAIRED, OK - Proceed to test step 7.

Test Step 5.

1. Test the purge pressure for the all wheel drive system.

Reference: Refer to Troubleshooting, "Sequence Valve - Test and Adjust".

Expected Result:

The purge pressure is correct.

Results:

• No - Proceed to test step 8.

• Yes - Stop.

Test Step 6.

1. Replace the charge pressure sequence valve. Use a new Caterpillar part for replacement.

Reference: Refer to Troubleshooting, "All Wheel Drive Flushing & Cooling Valve".Parts

Reference: Refer to Troubleshooting, "135-8016 VALVE GP-FLUSHING PIN 5AK74-UP. PART OF 8X-2519 VALVE & MTG GP-AWD".Specifications

Reference: Refer to Troubleshooting, "Flushing and Cooling Control Valve".

Expected Result:

The charge pressure sequence valve has been replaced.

Results:

• Continue - Proceed to test step 5.

Test Step 7.

1. Test the charge pressure for the all wheel drive system.

Reference: Refer to Troubleshooting, "Sequence Valve - Test and Adjust".

Expected Result:

The charge pressure is correct.

Results:

• No - Proceed to test step 6.

• Yes - Proceed to test step 5.

Test Step 8.

1. Replace the purge pressure sequence valve. Use a new Caterpillar part for replacement.

Reference: Refer to Troubleshooting, "All Wheel Drive Flushing & Cooling Valve".Parts

Reference: Refer to Troubleshooting, "135-8016 VALVE GP-FLUSHING PIN 5AK74-UP. PART OF 8X-2519 VALVE & MTG GP-AWD".Specifications

Reference: Refer to Troubleshooting, "Flushing and Cooling Control Valve".

Expected Result:

The purge pressure sequence valve has been replaced.

Results:

• Repair Complete - Stop.