D6T Track-Type Tractor Hydraulic System Operational Checks Caterpillar

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Do not check for leaks with your hands. Pin hole (very small) leaks can result in a high velocity oil stream that will be invisible close to the hose. This oil can penetrate the skin and cause personal injury. Use cardboard or paper to locate pin hole leaks.

The operation checks can be used to find abnormalities in the system. Raise and lower the blade and the ripper several times. Operate the tilt control valve until the tilt cylinder is fully extended and retracted several times. If equipped, operate the angle control valve until the angle cylinders are extended and retracted several times.

1. Watch the cylinders as the cylinders are extended and retracted. Movement must be smooth and regular.

2. Listen for abnormal noise from the system.

Tests for Cycle Times

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Hydraulic oil pressure can remain in the hydraulic system on this machine after the engine and pump have been stopped. Serious injury can result if this pressure is not released before any service is done on the hydraulic systems. In order to prevent possible injury, release the hydraulic system pressure before working on any fitting, hose, or hydraulic component. Lower all attachments to the ground before service is started. If the hydraulic system must be serviced, tested, or adjusted with the attachment in the raised position, the attachments and lift cylinders must be supported properly. Always move the machine to a location away from the travel of other machines. Be sure that other personnel are not near the machine when the engine is running and tests or adjustments are being made.

All tests for cycle times are performed with the engine at high idle.

The oil in the hydraulic system must be SAE 10 at a temperature of 65° ± 3°C (149° ± 5°F) in order to get the correct results.

If test results agree with the tables, the circuit is normal. Check the relief valve for the correct opening pressure. See Testing and Adjusting, "Main Relief Valve and Crossover Relief Valve - Test" in this module for the correct setting.

If only one of the cycle times is slow, check that circuit for cylinder drift.

Check these items if the cycle time is not correct.

1. Check the calibration of the controls.

2. Check pump efficiency.

3. Check the setting of the relief valve.

4. Check the cylinders for leakage.

5. Check the makeup valves for leakage.

6. Check the pressure limiter valve.

7. The valve spools in the bulldozer control valves and in the ripper control valve could be worn.

Drift Tests for Bulldozer Lift Cylinders

Test

1. Raise the blade off the ground. Shut off the engine. Leave the control lever in the HOLD position. Watch the lift cylinder rod for movement.

Drift Tests for Bulldozer Tilt Cylinder

Tests

1. Position the blade flat on the ground. Raise the front of the machine off the ground by lowering the right side of the blade to the TILT RIGHT position. Put the tilt control lever in the HOLD position. Shut off the engine. Watch the tilt cylinder rod for movement.

Drift Tests for Ripper Lift Cylinder

Tests

1. Raise the ripper off the ground. Put the control lever in the HOLD position. Shut off the engine and watch the ripper cylinder rod drift.

Steering Operation Checks

The steering operation checks indicate whether the operation of the steering circuit is normal.

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To prevent personal injury when checks are made while the machine is in operation, make sure only approved personnel are on the machine. Keep other personnel off the machine and in view of the operator. Make sure checks are done in an open area.

Steering Turn Diameter Check

1. Move the machine to an open area that is flat and dry. The ground conditions must limit the amount of track slip when the machine is turning.

2. Start the engine. Operate the engine at HIGH IDLE. Raise all of the implements to the full RAISE position. Return the controls to the HOLD position.

3. Release the parking brake. Put the transmission in FIRST GEAR FORWARD.

4. Move the steering control handle to the full STEER LEFT position. Keep all implement controls in the HOLD position.

5. Make a full turn of 360 degrees.

6. Stop the machine after the full turn. Lower all of the implements to the ground. Stop the engine.
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   Illustration 1	g00500963
   Steering check (A) Diameter of the turn

7. Measure distance (A). See Illustration 1.

   • XL Distance (A) should be 4 ± 0.5 m (13.1 ± 1.6 ft).

   • XW Distance (A) should be 4.5 ± 0.5 m (14.8 ± 1.6 ft).

   • LGP Distance (A) should be 5.1 ± 0.5 m (16.7 ± 1.6 ft).

   • XL VPAT Distance (A) should be 4.5 ± 0.5 m (14.8 ± 1.6 ft).

   • XW VPAT Distance (A) should be 4.9 ± 0.5 m (16.1 ± 1.6 ft).

   • LGP VPAT Distance (A) should be 5 ± 0.5 m (16.4 ± 1.6 ft).

8. Repeat Steps 2 through 7 with the steering control handle in the STEER RIGHT position.

9. If the distances in Steps 7 and in 8 are within the specification, the steering hydraulic system is operating correctly. If the distances in Steps 7 and 8 are not within the specification, proceed to Step 12.

Sprocket Speed Check

Note: The check should be used primarily in a shop area after the machine has been repaired or after the machine has been rebuilt.

1. Move the machine to a clear area that is level. Lower the implements to the ground. Stop the engine.

2. Separate the tracks. Remove the tracks from the sprockets on the final drives.

   Reference: Refer to Disassembly and Assembly, "Track - Separate" in the Service Manual for your machine.

3. Before the checks are performed, mark the sprockets of both final drives in order to count the revolutions during the checks.

4. Start the engine. Operate the engine at HIGH IDLE.

5. Release the parking brake. Move the steering control lever to the end of the travel in the STEER RIGHT position. Move the transmission to NEUTRAL.

6. This step checks the oil flow through the steering system. Use a stopwatch to count the number of revolutions per minute of each sprocket. Add the rpm of the right sprocket to the rpm of the left sprocket. The sum of the rpm of the left sprocket and of the right sprocket should be 25.75 ± 1.25 rpm.
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   Table 8

   A Check of the Sprocket Speeds for Steering Oil Flow
   Rpm of left sprocket		14.8 rpm
   Add rpm of right sprocket.	+	13.7 rpm
   Sum of the rpm of the sprockets	=	28.5 rpm

7. Do Steps 5 and 6 again with the steering control lever in the STEER LEFT position. The sum of the sprocket speeds for the full STEER LEFT position should be 25.75 ± 1.25 rpm.

8. If the sprocket speeds are not within the tolerances, check the operation of the components. If Step 6 is low, check the engine rpm.

9. If a problem had been indicated by the checks, use Diagnostic Instrument Tests to get a more accurate indication of the location of the specific problem.

10. If the values in Steps 5 and 6 for STEER RIGHT and for STEER LEFT are within the specification, perform the following calculation in order to check the steering balance: With the values from Step 5, subtract the value for STEER LEFT from the value for STEER RIGHT. The difference should be 0 ± 1.1 rpm.

11. If the sum in Step 10 is not within the specification, the steering to the right and to the left is not equal. Check that the displacement of the pump to the right and to the left is equal. The problem may be caused by a misadjusted pump control.

12. When the checks and the adjustments are complete, stop the engine. Remove all test equipment and connect the track.

    Reference: Refer to the topic Disassembly and Assembly, "Track - Connect" in the Service Manual for your machine.