797F Off-Highway Truck: Machine Preparation for Troubleshooting, Visual Inspection and Operational Checks

1.- Machine Preparation for Troubleshooting

WARNING: Off-Highway Truck Sudden movement of the machine or release of air or oil under pressure can cause possible injury or death to persons on or near the machine.To prevent possible injury or death, do the procedure that follows before testing and adjusting the Hydraulic System.

Note: Permit only one operator on the machine. Keep all other personnel away from the machine or in the operator's sight.

1. Move the machine to a smooth horizontal location. Move away from any machines that are working and any personnel.

2. Move the transmission shift lever to the NEUTRAL position. Activate the parking brakes.

3. Fully raise the dump body.

4. Stop the engine. Move the engine start switch to the OFF position.

5. Connect the retaining cables for the truck body to the rear of the truck.

6. Place blocks in front of the wheels and behind the wheels.

7. Ensure that all air pressure and all oil pressure is released before you perform any work on the hydraulic system. Refer to the Air System, "Specifications/Systems Operation/Testing and Adjusting" for more information.

The hydraulic system involves the hoist, brake cooling, brake actuation, and the gear pump for the motor drive for the rear axle oil pump. For more detailed information about the brakes, about brake cooling, or about the rear axle, refer to the following modules:

• Braking System, "Systems Operation/Testing and Adjusting"
• Power Train, "Systems Operation"
• Power Train, "Testing and Adjusting"

The steering system and the fan drive system is separate from the other hydraulic systems. For more detailed information about these systems, refer to the following modules:

• Steering System, "Systems Operation/Testing and Adjusting"
• Hydraulic Fan Drive, "Specifications/Systems Operation/Testing and Adjusting"

Troubleshooting can be difficult. There is a list of possible problems on the following pages. In order to repair a problem, refer to the problem and the probable causes that are listed.

This list of problems and probable causes will only give an indication of the existence of a possible problem and of the repairs that may be required. There are sometimes more repairs or other repairs that are required beyond the recommendations that are in the list. Remember that a problem is not normally caused by only one part. A problem is usually caused by the relation of one part with other parts. This list can not provide all possible problems and all probable causes. The service person must find the problem and the source of the problem. The service person must then perform the necessary repairs.

2.- Visual Inspection

A visual inspection of the hydraulic system and of the components is the first step in diagnosing a problem.

WARNING: 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.

NOTICE
Care must be taken to ensure that fluids are contained during performance of inspection, maintenance, testing, adjusting and repair of the machine. Be prepared to collect the fluid with suitable containers before opening any compartment or disassembling any component containing fluids. Refer to Special Publication, NENG2500, "Caterpillar Tools and Shop Products Guide", for tools and supplies suitable to collect and contain fluids in Caterpillar machines.Dispose of all fluids according to local regulations and mandates.

1. Check the hydraulic tank oil level. Add oil, if necessary. Refer to the Operation and Maintenance Manual, "Hydralic Tank Oil Level - Check" for more information.

2. Check all oil lines and the connections for any damage and/or leaks.

3. Check all pumps and the connections for any damage and/or leaks.

4. Follow the pump lines to the hydraulic tank and valves. Check the lines for any damage and/or leaks.

5. Check the hydraulic tank for any damage and/or leaks.

6. While the engine is running, use the oil sampling valves to obtain an oil sample. Check for air bubbles in the oil sample.

7. Remove the filter elements. Check for particles that were removed from the oil by the filter elements. A magnet will separate ferrous particles from nonferrous particles (piston rings, O-rings, or seals).

3.- Operational Checks

WARNING: Sudden movement of the machine or release of air or oil under pressure can cause possible injury or death to persons on or near the machine.To prevent possible injury or death, do the procedure that follows before testing and adjusting the Hydraulic System.

WARNING: When it is necessary to work under the machine with the body (bed) raised, attach the body (bed) retaining cables to the rear tow points. Install the rear tow point pins through the ends of the retaining cables.Failure to properly secure the body (bed) may result in personal injury or death.

1. Start the engine. Operate the engine at high idle.

2. Move the hoist control to the RAISE position. Hold the hoist control in the RAISE position for five seconds after the truck body is fully raised. Then, lower the truck body all the way to the truck frame.

3. Repeat Step 2 until the temperature of the hydraulic oil is above 38°C (100°F).

Lift Time for the Hoist Cylinders

1. Lower the truck body to the truck frame.

2. Operate the engine at high idle.

3. Raise the truck body to the fully raised position. Use a stopwatch to measure the required time.

The required time for full extension of the hoist cylinders is approximately 25 to 28 seconds. Refer to the Hydraulic System Testing and Adjusting, "Worksheets" for this machine in order to record the test results.

Power Down Time for the Hoist Cylinders

1. Raise the truck body to the fully raised position.

2. Operate the engine at high idle.

3. Use the power down function to fully lower the truck body to the truck frame. Use a stopwatch to measure the required time.

The time that is required to fully lower the hoist cylinders is approximately 18 to 20 seconds. Refer to the Hydraulic System Testing and Adjusting, "Worksheets" for this machine in order to record the test results.

Perform Step 1 through Step 3 for the float down time of the hoist cylinders. Refer to the Hydraulic System Testing and Adjusting, "Worksheets" for this machine in order to record the test results.

Cylinder Drift

Note: Perform this test with an empty truck body and hydraulic oil above 38°C (100°F).

1. Move the hoist control to the RAISE position.

2. When the first stage of the hoist cylinders is extended by 305 mm (12 inch), move the hoist control to the HOLD position.

3. The truck body will push the cylinder head of the first stage by 6.40 mm (0.25 inch) onto the second stage of the hoist cylinders. Use a stopwatch and record the required time.

The acceptable time for cylinder drift is relative to the temperature of the hydraulic oil in the hoist cylinders. See the following table.

Table 1

Acceptable Cylinder Drift
Minutes	Oil Temperature	Cylinder Drift
12.4	38°C (100°F)	6.40 mm (0.25 inch)
9.6	43°C (110°F)	6.40 mm (0.25 inch)
7.8	49°C (120°F)	6.40 mm (0.25 inch)
6.4	54°C (130°F)	6.40 mm (0.25 inch)
5.3	60°C (140°F)	6.40 mm (0.25 inch)
4.4	66°C (150°F)	6.40 mm (0.25 inch)
3.8	71°C (160°F)	6.40 mm (0.25 inch)
3.2	77°C (170°F)	6.40 mm (0.25 inch)
2.8	82°C (180°F)	6.40 mm (0.25 inch)

Excessive cylinder drift can be caused by the following conditions:

• Leaks in the lines between the hydraulic oil tank and the hoist cylinders
• Worn control valve spool
• Worn seals in the hoist cylinders

MARYGAR

797F Off-Highway Truck: Machine Preparation for Troubleshooting, Visual Inspection and Operational Checks 2012-12-01T08:05:00-08:00 Rating: 4.5 Diposkan Oleh: Unknown