992G Wheel Loader Electrohydraulic System Caterpillar

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Sudden movement or accidental starting of the machine can cause personal injury or death to persons on or near the machine. To prevent personal injury or death, perform the following: Park the machine on a smooth, level surface. Lower the work tool to the ground and engage the parking brake. Stop the engine and remove the key. Block the wheels and install the steering frame lock.

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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 work tools have been lowered to the ground, and the 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.

This test will help to determine if either the tilt cylinder or the main control valve is causing the drift problem. When the oil port at one end of the tilt cylinder is blocked, the tilt cylinder should not move during a drift test. If the tilt cylinder moves, there is internal leakage in the tilt cylinder.

Illustration 1	g01057315
Main Control Valve Group Location of the Ball Valve (Manual Lower)

Note: Before testing the machine for drift, ensure that the ball valve (manual lower) is blocking the flow of pilot oil to the hydraulic tank. The ball valve is located in the loader frame at the articulation hitch.

1. Connect the steering frame lock link.

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Illustration 2	g00287153
Hose Connections (Tilt Cylinder) (1) Hose connections for rod end.

2. Engage the parking brake.

3. Shift the transmission to neutral.

4. Start the engine. Warm the hydraulic oil to normal operating temperature of approximately 49 to 65°C (120 to 150°F).

5. Raise the bucket approximately 1 m (3.3 ft) off the ground. Keep the bottom of the bucket parallel to the ground. Place a support block under the lift arm and under the bucket. Lower the lift arm and the bucket onto the support blocks.

6. Stop the engine.

7. When the engine has stopped, turn the engine start switch to the ON position. Move the lift control lever and the tilt control lever in order to relieve the pressure in the implement hydraulic system. Then, turn the engine start switch to the OFF position.

   Reference: For additional information about relieving the pressure in the hydraulic system, refer to the Service Manual module Testing and Adjusting, "System Pressure - Release" for the machine that is being serviced.

8. Push in the plunger in the hydraulic tank breather in order to relieve the pressure in the implement hydraulic tank. Hold the plunger in position until all pressure is released from the implement hydraulic tank.

9. Install a 5P-0049 Cover and a 1P-3705 Seal at the connections for both ends of the hose for the rod end of the tilt cylinder.

10. Remove the support block from the bucket. Check the distance of rod movement in 1.7 minutes. For a new cylinder, the maximum rod movement in 1.7 minutes is 25 mm (1.0 inch).

11. If the drift is within the specifications, the main control valve is probably causing the drift problem. If there is too much drift, the tilt cylinder has an internal leak. Look for a scored cylinder or worn piston seals.

12. Place the support block under the bucket. Make sure that the weight of the bucket is on the support block.

13. Relieve the pressure in the hydraulic system.

    Reference: For additional information about relieving the pressure in the hydraulic system, refer to the Service Manual module Testing and Adjusting, "System Pressure - Release" for the machine that is being serviced.

14. Remove the covers and the seals from the hose connections at the rod end. Reconnect the hoses.