COMPRESSOR GP 1613632 - Caterpillar

Introduction
This Special Instruction provides a troubleshooting procedure for bucket drift on certain 336E Excavators. Do not perform this procedure until you have read and understand the information.Troubleshooting Procedure
Note: The following troubleshooting procedure should be performed with the hydraulic oil temperature at 55° 5°C (131° 9°F).
Determine if the machine has a quick coupler control circuit installed. If so, remove the quick coupler pressure tap from the bucket head end tube to remove potential leak path from the bucket circuit. If a change in bucket drift was detected, refer to ""Repair Options for Machines with Quick Coupler Control Circuits"". If not, move to Step 2.Note: The test above can be completed without a quick coupler installed on the machine. Only the quick coupler control circuit is required.
Install 6E-4816 Control Valve Plug Gp in place of bucket line reliefs and test bucket drift. If drift goes away, replace line reliefs. If drift is still present, move to Step 3.
Test for cylinder drift with the cylinder isolated from the rest of the hydraulic system by blocking the load supporting port of the cylinder while venting the other port. If cylinder drift is present, inspect the cylinder. If cylinder does not drift, move to Step 4.
Reverse / cross the bucket cylinder head and rod lines at the main valve to see if leakage changes direction. If drift changes direction, this signifies one port of the valve has more leakage than the other. If drift does not change direction then either both valve ports have leakage (should see drift in both directions) or there is a leak path outside the valve that was missed in the previous steps.
If the testing steps indicate main valve leakage, remove the bucket spool and inspect both the spool and bore for scratches / damage. If the valve bore looks OK, install a new service spool.
If testing identifies valve leakage and the spool bore is damaged or a replacement spool does not resolve bucket drift, the Technical Communicator (TC) should contact the Dealer Solution Network (DSN) to find out if there are any new troubleshooting techniques or service options before replacing the main valve.Repair Options for Machines with Quick Coupler Control Circuits
If the 336E Excavator experiences coupler control valve leakage, three repair options are advised.
Repair or replace quick coupler solenoid valve and manifold group with same part.
Replace the quick coupler control kit with the ISO Cat pin grabber coupler control kit. The pin grabber coupler control kit is required if the machine will have a new Cat pin grabber coupler installed in the future. Reference Product Bulletin, GEJQ1298, "Cat Pin Grabber Couplers for Cat 311–349 Excavators" for the proper Cat pin grabber coupler control kit based on machine serial number and currently installed coupler control system.
If the machine is equipped with a center lock hydromechanical conversion kit, it can be modified per Special Instruction, SEHS0071, "Procedure to Modify the Hydromechanical Conversion Kit on Certain 336E Excavators".