TANK A 0395513 - Caterpillar

Introduction
The problem that is identified in the technical information bulletin that follows does not have a known permanent solution. Until a permanent solution is known, use the solution that is identified below.Problem
The tilt cylinder of the 988G Wheel Loader works in the opposite fashion from the 988F Wheel Loader. On the 988G Wheel Loader, the oil flows to the head end of the tilt cylinder when the bucket is dumped. On the 988F Wheel Loader, the oil flows to the rod end of the tilt cylinder when the bucket is dumped. When a full bucket is dumped on the 988G Wheel Loader, gravity increases the speed of the bucket. This increases the volume in the head end of the tilt cylinder. The larger volume causes voids to develop in the head end of the tilt cylinder. The makeup valve and pump flow cannot provide enough oil in order to fill the head end of the cylinder. If the bucket is dragged in reverse after dumping, the position of the bucket will change. The bucket will rack back until the void in the head end of the tilt cylinder is eliminated.Solution
Dump a loaded bucket at high idle in order to minimize voiding in the tilt cylinder. At high idle, the pump will turn 2.5 times faster. This will provide 2.5 times more oil flow at high idle versus low idle. Use the throttle lock at high idle in order to maintain high engine speed and high pump flow.The following technique can be used to minimize air in the tilt cylinder. After dumping a full bucket, move the bucket away from the bucket stop. It is important to move the bucket away from the stops in order to move the software out of Dump Structural Protection. This will also provide full flow to the tilt circuit.In order to drag the bucket in reverse after dumping, maintain high engine speed while the bucket is dumped. Partially rack back the bucket while the bucket is lowered. Dump the bucket to the desired position. Hold the lever in the DUMP position until resistance is felt. This will ensure that the head end of the tilt cylinder is full of oil. This will enable the bucket to hold the position.Other solutions are being investigated.Note: The software has Dump Structural Protection. This reduces oil flow when the bucket is near the dump stops (full dump). This prevents filling the void in the head end of the tilt cylinder rapidly when the bucket is in the DUMP position.Changes to the software that allow full pump flow after dumping are being tested on 988G Wheel Loaders with the S/N:BNH serial number prefix. The new software will allow the tilt cylinder head to be filled in a few seconds if the tilt control lever is held in the DUMP position. Changes in production are planned for November 2003 in order to provide this software for machines with the S/N:BNH and ; S/N:2TW serial number prefixes.