AD55 Underground Articulated Truck Power Train Caterpillar

Gear Pump (Transmission Charging and Torque Converter Scavenge) - Test and Adjust

Usage:

AD55 ANW

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Table 1
Required Tools
Part Number	Part Description	Qty
6V-3079	Hose As	1
6V-4143	Coupler	2
8T-0856	Pressure Gauge (0 to 6,000-kPa (0 to 870-psi))	1

Note: Make sure that the filters and the screens are clean before you test any pressures. Make sure that the oil is at operating temperature before you perform this test.

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Personal injury or death can result from sudden machine movement.

Sudden movement of the machine or the release of oil under pressure can cause injury to persons on or near the machine. To prevent possible injury before testing and adjusting the power train system, perform the procedure in the Testing and Adjusting, Troubleshooting, "General Information" section.

This test will show the following conditions if the conditions exist:

The transmission charging section of the gear pump is good.
The relief valve of the selector and pressure control valve is correctly set.

Procedure

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Illustration 1	g01082236
Right side of the transmission case (F) Pressure tap for charging pressure of the transmission

Use a coupler and a hose to connect a 8T-0856 Pressure Gauge (0 to 6,000-kPa (0 to 870-psi)) to the nipple at pressure tap (F).
With the parking brake engaged, start and run the engine at low idle rpm with the transmission in NEUTRAL. The pressure on the gauge should be a minimum of 2690 ± 35 kPa (390.0 ± 5.0 psi).
Run the engine at high idle rpm with the transmission in NEUTRAL. The maximum pressure on the gauge should be 3205 kPa (465.0 psi).
When this test is complete, stop the engine and remove the test equipment.

Problem: The oil pressure is too low at low idle and the oil pressure is too low at high idle.

Probable Cause:

Failure of the transmission charging pump section.
There are bad seals in a clutch of the transmission. Refer to Testing and Adjusting, "Transmission Hydraulic Control Clutch Pressure - Test".

Problem: The oil pressure is too low at low idle and the oil pressure is correct at high idle.

Probable Cause:

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Illustration 2	g01082240
Selector and pressure control valve (1) Relief valve (2) Spacers

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Table 2
Chart of Spacers for the Relief Valve ⁽¹⁾
Part No. for the Spacers	Thickness of the Spacers	Change in Pressure as a Result of One Spacer
145-0105 Spacer	0.25 mm (0.010 inch)	41 kPa (6.0 psi)
145-0106 Spacer	0.90 mm (0.035 inch)	145 kPa (21.0 psi)
145-0107 Spacer	1.60 mm (0.063 inch)	261 kPa (38.0 psi)

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⁽¹⁾	Before an adjustment is made, be certain that the valve spring is not weak or broken.

The setting of relief valve (1) is too low. Add spacers (2). Refer to Table 2. Adjust the relief valve to the low idle setting.
There are bad seals in a clutch of the transmission. Refer to Testing and Adjusting, "Transmission Hydraulic Control Clutch Pressure - Test".