the pilot bearingis not used when the truck is under load, it is only when shifting that the bearing is used right?
Its not related to load. If the clutch is disengaged then its not in use. If the clutch is engaged then its in use. Try to think about it this way, when ever the engine speed is varrying from the transmission speed then the pilot bearing is being used. For instance if you are stopped and you have the clutch pedal all the way down: The engine is still turning but the transmission is not.
If the trans the clutch is disengaged then the pilot is just sitting there. Under power, cruising, coasting, even if you are coasting in netural, if the clutch is not in use then neither is the pilot.
What exactly does the pilot bearing do? keep the input shaft rotating at speed so that it will go into the next gear?
