TK741, TK751 and TK752 Track Feller Bunchers Machine Systems Caterpillar

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Hot oil and components can cause personal injury. Do not allow hot oil or components to contact skin.

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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 system. In order to prevent possible injury, release the hydraulic system pressure before working on any fitting, hose, or hydraulic component. Lower all work tools to the ground before service is started. If the hydraulic system must be serviced, tested, or adjusted with the work tool in the raised position, the work tool 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.

Note: Use the information in the reference to prepare the machine for this test. Also, use the information in the reference to relieve any system pressure that may be present in the hydraulic system.

Reference: For the correct procedure to prepare the machine for this test, refer to Testing and Adjusting, "Machine Preparation for Troubleshooting" for the machine that is being serviced.

Reference: For the correct procedure to relieve any hydraulic oil pressure that may be present in the hydraulic system, refer to Testing and Adjusting, "System Pressure - Release" for the machine that is being serviced.

Use the following procedures to purge air from the main hydraulic system and the pilot hydraulic system.

Main Hydraulic System

There are several opportunities for air to enter the main hydraulic system.

• Filling a hydraulic tank after the tank has been drained.

• Filling a hydraulic tank after a hydraulic line has been removed.

• A hydraulic component is replaced or removed.

• Any portion of the hydraulic system is opened.

If air is trapped in the system the following conditions may exist.

• Irregular movement of the cylinders

• The implement controls do not respond.

• Intermittent motion of implements

To resolve this problem, use the following procedure to remove the air from the hydraulic system.

1. Release all hydraulic system pressure. Refer to the reference at the beginning of this procedure.

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Illustration 1	g00938045
Main Pump

2. Remove plug (2) from port (R1) on the main pump. Pour oil into the pump until oil comes out of the port (R1). Install plug (2). Remove plug (1) from port (R3) on the main pump. Pour oil into the pump until oil comes out of the port (R3). This will eliminate the air in the pump and this will also fill the case of the pump with oil. Install plug (1) .

3. Start the engine.

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Illustration 2	g00827520
Older models

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Illustration 3	g01162712
Newer models

4. Place the hydraulic lockout control in the UNLOCKED position.

5. Cycle all implements through the full range of motion. Cycle the implements several times.

   Note: Cycling cylinders and other implements should force trapped air out of the main hydraulic system.

6. Shut off the engine.

7. Release all hydraulic system pressure. Refer to the reference at the beginning of this procedure.

8. Slightly crack plug (1) at port (R3) .

9. Wait for approximately four minutes in order to allow the air to rise out of the hydraulic oil.

10. Tighten plug (1) .

11. Check the hydraulic fluid level after you actuate any cylinders, pumps, or motors. Top off the fluid level, if necessary.

Pilot Hydraulic System

Air can be trapped in the pilot hydraulic system. Air that is trapped in the pilot hydraulic system may shift a control valve spool. If a control valve spool is shifted, the corresponding implement could move. Trapped air can also be responsible for cylinder drift.

If the pilot hydraulic system has been opened, follow the procedure to release the air that is trapped in the pilot hydraulic system.

Note: Most of the air should work out of the system when all of the implements are cycled. If air remains in the system, follow the procedure below in order to release the air.

1. Shut off the engine.

2. Release all hydraulic system pressure. Refer to the reference at the beginning of this procedure.

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Illustration 4	g01053635
Air Purge Plugs for Pilot System (3) Implement Control Valve (7 Bank)

3. The following control valves are part of the implement control valve for the felling head: boom, tilt, stick, swing, grapple arms, accumulator arms and tool.

   Note: The air purge plugs are located on both ends of the control valves.

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Illustration 5	g01075430
Air Purge Plugs for Pilot System (4) Travel Control Valve

4. The following valves are part of the travel control valve: left track and right track

   Note: The air purge plugs are located on both ends of the control valves.

   Note: The travel control valve can be equipped with a side leveling control valve and a forward leveling control valve. The air purge plugs are located on both ends on the control valves.

5. Slightly crack the air purge screw for the implement that does not function correctly. Keep the air purge screw cracked until a small amount of oil seeps out of the purge screw.

6. Tighten the air purge screw.