773E and 775E Off-Highway Truck Hydraulic System: Control Valve (Hoist) - Test and Adjust & Hoist Cylinder Performance - Test

1.-Control Valve (Hoist) - Test and Adjust

Table 1

Tools Needed	Qty
6V-7830 Pressure Gauge	1
Electronic Service Tool	1
JERD2124 Electronic Technician (ET) (Single User License)	1
JERD2129 ET Data Subscription	1
171-4400 Communication Adapter Gp	1

The command for the hoist control valve is adjustable. The adjustment range is -5 to +5 with zero as a default. A positive adjustment will increase the command to the hoist control valve. A positive adjustment causes the body to come down faster. A negative adjustment will decrease the command to the hoist control valve. A negative adjustment causes the body to lower more slowly.

Note: The adjustment to the hoist control valve may not be available on some early ECM systems. On some early machines, the adjustment range may be from zero to 10 with 5 as the default on these early ECM systems.

(1) Pressure tap

1. Connect a 6V-7830 Pressure Gauge on the pressure tap (1) of the gear pump for the hoist and rear brake.

(2) Communications port for ET



2. Install the Electronic Technician (ET) to the communications port (2) that is located in the cab.

3. Use the drop-down menu in ET in order to obtain the screen for "Transmission ECM configuration".

4. With the body in the down position, place the hoist lever in the HOLD position.

5. Use the ET in order to change the setting for the hoist control valve to the desired setting between -5 to +5. The procedure begins at zero. Change the setting of the hoist control valve one increment at a time. A positive change or the negative change can be made to the setting.

6. Raise the body to the full up position.

7. Place the hoist lever in the FLOAT position. Check the body down snub function as the body lowers to the frame.

8. If further adjustment is required repeat Steps 3 through Step 7.

9. In order to check pressure in the outlet port of the hoist, the hoist status must be in the SNUB mode on the "Transmission ECM configuration" status screen in ET.

10. Run the engine at high idle with the hoist control in the FLOAT position.

Note: If the pressure is greater than 1725 kPa (250 psi), the adjustment for the command to the hoist control valve is too high. A setting to the control that is too high causes excessive oil to be diverted to the hoist control valve. Diverting too much oil will cause overheating of the brake oil when the body is in the FLOAT position. Repeat steps 3 through step 7 and lower the adjustment for the hoist control valve.

2.-Hoist Cylinder Performance - Test

WARNING: Personal injury or death can result from sudden machine movement. Sudden movement of the machine or release of air pressure or oil pressure can cause injury to persons on or near the machine.To help prevent possible injury before testing and adjusting any air system or hydraulic system, perform the procedure in the Testing and Adjusting, "General Information" section.

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 dump body is fully raised. Then, lower the dump 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 Hoist Cylinders

1. Lower the dump body to the truck frame.

2. Operate the engine at high idle.

3. Raise the dump 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 11 seconds.

Cylinder Drift

Note: Perform this test with an empty dump 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 dump body will push the cylinder head of the first stage by 6.35 mm (0.250 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 Table 1 for the acceptable time.

Table 1

Acceptable Cylinder Drift
Minutes	Oil Temperature	Cylinder Drift
7.0	38° to 48°C (100° to 119°F)	6.35 mm (0.250 inch)
4.1	49° to 64°C (120° to 149°F)	6.35 mm (0.250 inch)
3.0	65 °C (150 °F)	6.35 mm (0.250 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

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773E and 775E Off-Highway Truck Hydraulic System: Control Valve (Hoist) - Test and Adjust & Hoist Cylinder Performance - Test 2013-01-10T19:14:00-08:00 Rating: 4.5 Diposkan Oleh: Unknown