784C and 785C Off-Highway Truck/Tractors Steering System Caterpillar

The pressure setting of the backup relief valve is 20700 ± 400 kPa (3000 ± 60 psi) at a flow of 8 ± 2 L/min (2.1 ± 0.5 US gpm). The relief valve must be removed. Use a bench test to achieve an accurate pressure test. The bench test is needed because other components in the steering system will keep the pressure from reaching this value.

Illustration 1	g00281966
Solenoid and Relief Valve (1) Port to right accumulator (2) Port for Auxiliary Power Unit (3) Inlet port (4) Port to left accumulator (5) Port to steering metering pump (6) Nut (7) Setscrew (8) Backup relief valve

Illustration 2	g00302103
Solenoid and Relief Valve (1) Port to right accumulator (2) Port for Auxiliary Power Unit (3) Inlet port (4) Port to left accumulator (5) Port to steering metering pump (6) Nut (7) Setscrew (8) Backup relief valve

A functional test of the relief valve may be performed on the machine.

1. Remove the hydraulic oil lines from ports (1), (4) and (5) .

2. Use Tool (A) to block all three ports.

   Note: Step 2 prevents the accumulators from filling during the test.

Note: Port (3) does not need to be blocked. The check valve that is mounted in port (3) prevents oil from flowing back into the pump.

3. Install a tee in port (2). Connect the outside hydraulic source to the tee. Connect an 8T-0860 Pressure Gauge to the tee. Apply pressure.

   Note: A pressure reading of 19400 ± 350 kPa (2800 ± 50 psi) is an acceptable reading. The pump supply cannot produce the necessary oil flow that is required to accurately check the relief valve.

Use the following procedure to change the pressure setting of backup relief valve (8) :

Note: Backup relief valve (8) must be adjusted on the stand.

1. Loosen nut (6) .

2. Turn setscrew (7) clockwise in order to increase the pressure setting.

   1. Turn setscrew (7) counterclockwise in order to decrease the pressure setting.

      Note: One revolution of setscrew (7) will change the pressure setting by 4730 kPa (686 psi).