TROUBLESHOOTING COMMON PROBLEMS Suspension Charging The Payload Meter II™ is a reliable controller and is rarely the source of failure in calculating payloads. The single most common cause for an inaccurate payload estimate is improper suspension charging. Often maintenance per- sonnel will not take the time to properly drain a suspension and carefully recharge it with oil and nitrogen. Most often technicians will simply 'gas up' the suspensions with more nitrogen and send a truck back into service. Komatsu engineers have conducted tests at customer sites to monitor suspension charging on trucks and found many trucks to be improperly charged.
Trucks with poorly charged suspensions were sent to service bays for main- tenance by mine personnel. In some cases these trucks were returned to operation in worse condition than when they were first checked because service personnel did not take the time to carefully charge the suspensions. The payload meter uses the pressures from the suspensions to calculate payload. As the truck is loaded, a flat suspension will completely collapse. The top suspension cap will make metal-to-metal contact with the bottom. This often occurs in the rear suspensions.
The pressure in the suspension will not accurately reflect the force applied to the suspension by the weight of the material in the body and inaccurate payload calculations will result. In addition to inaccurate payload calculations, improperly charged suspensions increase wear-and-tear on truck frames and tires, increasing maintenance costs over the life of the truck. Each over-loaded haul cycle with under- charged suspensions leads to premature failure. Consistently low payload estimates are the first sign that the sus- pensions are not being properly maintained and the truck is on a path toward increased operating costs and system failures.
Thankfully, the effects of improper suspension charging can be postponed with proper service and care. Specific suspension charging procedures for each truck model can be found in the shop manual. In general, the following items are very important for proper charging: Completely discharge the suspension. This may take more than an hour for the nitrogen and oil to com- pletely discharge. However, to ensure that the proper volume of fresh oil is added, it's necessary to remove as much of the oil/nitrogen mixture as possible. Fill the suspension to the proper height with fresh oil, this is critical to keeping the suspensions from bottom- ing out.
Charge the suspension to the proper height with nitrogen. Refer to Section “H” for the proper charging procedures. This module contains an example of how to use the Scope program from Komatsu to monitor suspension pressure data. M20007.2 3/02 Payload Meter II™ Troubleshooting M20-35