385B Excavator Hydraulic System Caterpillar

Margin pressure is the difference between the pump discharge pressure and the load sensing signal pressure. Each pump must be isolated and tested separately. The pump that is not being tested must remain at low pressure standby. In order to isolate one of the pumps, disconnect the load sensing signal from the pump that is not being tested.

Front Pump

1. Position the machine on level ground.

2. Stop the engine.

3. Release the pressure in the hydraulic system. Refer to Testing and Adjusting, "Hydraulic System Pressure - Release".

Show/hide table



Illustration 1	g00725816
(A) 8T-0861 Pressure Gauge (B) Pressure differential gauge group (C) Test hose (D) Test hose

Show/hide table



Illustration 2	g00853523
Main pump (front view) (1) Pressure tap (front pump delivery pressure) (2) Pressure tap (rear pump delivery pressure)

4. Connect test hose (C) between the pressure differential gauge group and pressure tap (1) .

Show/hide table



Illustration 3	g00854351
Main pump regulators (3) Tee (4) Load sensing line (5) Rear pump regulator (7) Front pump regulator

5. Disconnect load sensing line (4) from tee (3) of front pump regulator (7). Install 6V-8397 O-Ring Seal and 6V-9508 Face Seal Plug in the open end of load sensing line (4). Leave the port on tee (3) open to atmospheric pressure.

   Note: Disconnecting load sensing line (4) causes the rear pump to remain at low pressure standby during the margin pressure test procedure for the front pump.

Show/hide table



Illustration 4	g00856849
(D) Test hose (3) Tee (4) Load sensing line (6) 6V-3965 Pressure tap (load sensing signal) (7) Front pump regulator (11) 8T-8902 Tee (12) 6V-9829 Cap As (13) 3J-1907 O-Ring Seal (14) 6V-8397 O-Ring Seal

6. Install seal (14) and tee (11) to tee (3) .

7. Install seal (14) and cap (12) on tee (11) .

8. Install seal (13) and pressure tap (6) in tee (11) .

9. Connect test hose (D) between the pressure differential gauge group and pressure tap (6) on front pump regulator (7) .

10. Connect pressure gauge (A) to the pressure differential gauge group. This pressure gauge is used to monitor the pump delivery pressure.

Rear Pump

1. Position the machine on level ground.

2. Stop the engine.

3. Release the pressure in the hydraulic system. Refer to Testing and Adjusting, "Hydraulic System Pressure - Release".

Show/hide table



Illustration 5	g00725816
(A) 8T-0861 Pressure Gauge (B) Pressure differential gauge group (C) Test hose (D) Test hose

Show/hide table



Illustration 6	g00853523
Main pump (front view) (1) Pressure tap (front pump delivery pressure) (2) Pressure tap (rear pump delivery pressure)

4. Connect test hose (C) between the pressure differential gauge group and pressure tap (2) .

Show/hide table



Illustration 7	g00854388
Main pump regulators (4) Load sensing line (5) Rear pump regulator (7) Front pump regulator (8) Pressure tap (load sensing signal) (9) Load sensing port (front pump) (10) Load sensing line

5. Disconnect load sensing line (4) and load sensing line (10) from port (9) of front pump regulator (7). Connect load sensing line (4) to load sensing line (10) with 6V-8730 Face Seal Union. Leave port (9) of the front pump regulator open to atmospheric pressure.

   Note: Disconnecting load sensing line (4) and (10) from front pump regulator (7) causes the front pump to remain at low pressure standby during the margin pressure test procedure for the rear pump.

6. Connect test hose (D) between the pressure differential gauge group and pressure tap (8) on rear pump regulator (5) .

7. Connect pressure gauge (A) to the pressure differential gauge group. This pressure gauge is used to monitor the pump delivery pressure.

Test and Adjust

The front pump and the rear pump must be tested separately. Use the following procedure in order to test and/or adjust the margin pressure for each pump.

1. Start the engine.

Show/hide table



Illustration 8	g00726210
(C) Display for Digging Mode (D) Key for Digging Mode

2. Place the machine controls at the following settings: Engine speed dial "10", AEC switch OFF, Digging Mode and Gain/Response (normal). Refer to Testing and Adjusting, "Engine Performance - Test" for engine rpm settings.

3. Place the hydraulic activation control lever in the UNLOCKED position.

4. Increase the hydraulic oil temperature to 55° ± 5°C (131° ± 9°F).

5. On the VIDS keypad, select the VIDS parameter "890" in order to display the amperage to the boom raise solenoid.

   Reference: Refer to Systems Operation, RENR3102, "Vital Information Display System (VIDS)", "Keypad".

6. Slowly move the joystick for the boom to the BOOM RAISE position until the amperage reading on the display is "1.00". Hold the joystick for the boom in this position and read the margin pressure on gauge (C). The margin pressure should be 1960 ± 100 kPa (285 ± 15 psi).

7. Return the joystick for the boom to the NEUTRAL position.

Show/hide table



Illustration 9	g00891005
(5) Rear pump regulator (7) Front pump regulator (11) Locknut (12) Adjustment screw (13) Locknut (14) Adjustment screw

8. If the margin pressure is not within the specification, adjust the margin pressure setting for the pump that is being tested. Loosen locknut (11) and turn adjustment screw (12) in order to adjust the front pump regulator. Loosen locknut (13) and turn adjustment screw (14) in order to adjust the rear pump regulator.

Note: Turn the adjustment screw clockwise in order to increase the margin pressure. Turn the adjustment screw counterclockwise in order to decrease the margin pressure.

Note: In order to avoid excessive leakage during the adjustment of the margin pressure, loosen the locknut only far enough so that the adjustment screw can be turned.

Note: Always make the final pressure adjustment on the pressure rise.