2000/12/04 Caterpillar

Off-Highway Truck/Tractor:

784C (S/N: 2PZ1-UP)

785 (S/N: 8GB1-UP)

785B (S/N: 6HK1-UP)

785C (S/N: 1HW1-UP; APX1-UP)

785C HAA (S/N: 5AZ1-UP)

789 (S/N: 9ZC1-UP)

Service Magazine SEPD0553, 04 December 2000, "A New Steering Pump and a New Adapter are Used". Disregard this article. Refer to the article that follows.

Description of Change: A new steering pump and a new adapter are used on the 784C Off-Highway Tractors and on the 785C Off-Highway Trucks.

Adaptable To: The new 190-2279 Piston Pump and the new 191-0126 Adapter are direct replacements for the nonserviceable 184-4503 Piston Pump and for the nonserviceable 4T-0382 Piston Pump. The new 190-2279 Piston Pump and the new 191-0126 Adapter are effective with the following machines: 784C (S/N: 2PZ1), 785C HAA (S/N: 5AZ274) and 785C (S/N: APX169). The new steering pump and the new adapter are adaptable to the following machines: 785 (S/N: 8GB), 785B (S/N: 6HK), 785C HAA (S/N: 5AZ1-273), 785C (S/N: 1HW; APX1-168) and 789 (S/N: 9ZC).

Procedure to Adjust the Pressure

The new pump's pressure compensator has a pressure control valve that is adjusted with a screw. The pressure control valve for the former steering pump required shimming in order to make pressure adjustments. The compensator that is used in the new pump is designed for use in a load sensing hydraulic system. The steering system on the truck is constant flow with high pressure cutoff control. The compensator on the new pump must be adjusted in order to prevent the load sensing region of the valve from operating. If the load sensing spool in the valve is not adjusted correctly, the steering system may experience sluggish operation. Use the following procedure to adjust the pressure setting of the new pump.

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Illustration 1	g00880464
The 193-3182 Pressure and Flow Compensator Valve (1) is part of 190-2279 Piston Pump .

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Illustration 2	g00880542
193-3182 Pressure and Flow Compensator Valve

1. Remove the cover and loosen the locknut on adjustment screw (A) .

2. Turn adjustment screw (A) clockwise until the screw stops. The load sensing spool will be blocked from movement.

3. Tighten the locknut to a torque of 21 N·m (15 lb ft).

4. Install the cover and tighten to a torque of 21 N·m (15 lb ft).

5. Remove the cover and loosen the locknut on adjustment screw (B) .

6. Turn adjustment screw (B) in order to achieve the maximum pressure setting. The maximum pressure setting is 17580 ± 345 kPa (2550 ± 50 psi).

7. Tighten the locknut to a torque of 21 N·m (15 lb ft).

8. Install the cover and tighten to a torque of 21 N·m (15 lb ft).