BEARING-L. 7B6932 - 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 material from the oil sand mines in Canada has a thick consistency and a sticky consistency. Oil sand mines are reporting a rapid center of gravity shift on 797, 797B, and 797F Off-Highway Trucks during the DUMP cycle. During the DUMP cycle, the material will slide out of the truck body in a large mass versus a gradual release from the truck body. This situation is referred to as "loafing".When the mass of material slides toward the rear of the truck body, the center of gravity of the truck shifts toward the rear of the truck until the mass of material falls from the truck body. As the mass slides toward the rear of the truck, the shift in the center of gravity causes the front of the truck to rise and the front struts to extend.After the mass slides out of the truck body, the center of gravity will rapidly return to the normal position. This shift in the center of gravity causes a severe jar to the truck, the cab, and the operator.The 165-2489 Relief Valve Gp for the hoist cylinder is properly set. The chassis ECM contains the correct software.In the field, devices have been installed in the truck body that split the load in order to prevent the rapid shift in the center of gravity. A device was designed to prevent the truck from "overcentering". The attempts did not work.Solution
In order to minimize the effects of "loafing" on the 797, 797B, and 797F Off-Highway Trucks that operate in the oil sand mines, increase the setting on the 165-2489 Relief Valve Gp for the rod end of the hoist cylinder to 28500 700 kPa (4100 100 psi). The setting on the relief valve for the rod end of the hoist cylinder should never exceed 28950 kPa (4200 psi).