CONNECTOR AS-EXHAUST 8N4709 - Caterpillar

Introduction
The problem that is identified below does not have a known permanent solution. Until a permanent solution is known use the solution that is identified below.Problem
Some Excavators listed above have had problems with the boom drift reduction valve at early hours. The pilot shuttle valve may shift at higher pressures than originally designed. When the joystick for boom down is engaged, there will be no boom response.Drift reduction valves have been reported to unlock at 1241 kPa (180 psi) to 1517 kPa (220 psi) of pilot pressure. The valves are designed to unlock at 690 kPa (100 psi) to 827 kPa (120 psi).Solution
Refer to the following steps to test the boom drift reduction valve.
Use a tee with a test port on either signal side to install a proportional reduction valve. The proportional reduction valve is placed on the pilot line at the boom 1 spool cap.
Start the Excavator
Adjust the proportional reduction valve until the boom 1 spool signal pressure is 827 kPa (120 psi). The remainder of the signal circuit should be greater than 1517 kPa (220 psi).
Move the joystick to boom down.If there is no boom response during this test, then replace the existing proportion reduction valve with 255-5683 Load Control Valve Gp .