PLATE 3026333 - Caterpillar

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.
Care must be taken to ensure that fluids are contained during performance of inspection, maintenance, testing, adjusting and repair of the product. 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 on Caterpillar products.Dispose of all fluids according to local regulations and mandates.
Note: Before you perform any tests, visually inspect the entire hydraulic system for oil leaks and for damaged components.The 8T-5320 Hydraulic Test Group and the 4C-4890 Hydraulic Test Group may be used to test the pressure at the pressure taps.
Illustration 1 g00502899
Location of pressure taps for the hoist and rear brake cooling gear pumpThe hoist dual stage relief valve is part of the hoist control valve. The hoist control valve is located under the truck. The relief pressure for the RAISE position is different from the relief pressure for the LOWER position.Relief Valve Test (High Pressure)
Lower the dump body completely. Stop the engine.
Relieve any system pressure that may be present. Move the hoist control to the RAISE and LOWER positions. Place the hoist control in the FLOAT position.
Connect two hose assemblies to two 8T-0860 Pressure Gauges. Connect the hose assemblies to both of the pressure taps on the hoist and rear brake cooling gear pump. Make sure that the hoses for the pressure gauges are long enough to be extended into the cab.
Start the engine. Operate the dump body repeatedly until the temperature of the hydraulic oil is above 38 °C (100.0 °F).
Run the engine at LOW IDLE. Move the hoist control to the RAISE position until the cylinders are fully extended. Attach the safety cable for the dump body.
Slowly accelerate the engine to the HIGH IDLE position. Hold the hoist control in the RAISE position. The pressure range for the 785C and 789C machines is 17225 to 17925 kPa (2500 to 2600 psi). The pressure range for the 793C machines is 20370 to 21070 kPa (2955 to 3057 psi). Record the highest pressure that is read on the gauge. If the pressure exceeds this range, investigate the cause of the higher pressure.
If the pressure setting is incorrect, adjust the relief valve on the hoist diverter valve. Refer to "Relief Valve Adjustment" within the original Service Module for the correct procedure.
Raise the dump body completely. Remove the safety cable.
Illustration 2 g00283734
High pressure relief valve (1) 5J-2721 Shim (2) 5J-2722 Shim
As needed, adjust the number of shims in order to achieve the correct relief valve pressure setting.
Table 1
Shims for Adjusting the Relief Valve Pressure Setting    
Part Number     Thickness