TIRE & RIM GP 1543933 - 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
Machines that are configured with tool control system 14 and a hydraulic thumb may experience failures of the thumb cylinder. The cylinder may fail if the bucket is curled into the thumb and the circuit for the thumb is not activated. The pressure relief is not active for the thumb cylinder if the tool control system is not activated.The circuit for the tool control is typically activated from the joystick slide control on the right hand pilot control valve. Until the relief valve opens in the circuit for the F2 auxiliary control valve, the thumb cylinder receives excessive stress from the curl of the bucket into the thumb. The excessive stress will typically cause a failure of the thumb cylinder.Solution
If a thumb is installed with tool control system 14, the relief pressure of the F2 auxiliary control valve must be reset to the pressure relief setting for the thumb cylinder. The line relief setting of the F2 auxiliary control valve defines the maximum pressure at the head end of the thumb cylinder. Refer to the Testing and Adjusting Manual, "Excavator Tool Control Systems" that is appropriate for your machine in order to reset the relief pressure of the F2 auxiliary control valve.