The reality of today’s truck shop is that truck technicians seldom are called upon to rebuild alternators. It is our task to diagnose a failure and then, if necessary, replace a defective alternator with a rebuilt unit. However, it is good learning practice for trainee technicians to understand what is required to overhaul an alternator because it can greatly improve diagnostic skills.
The alternator we are going to use as our model for overhaul is the medium-duty Delco 40SI unit. The 40SI is used for electrical systems requiring up to 300 amp alternators but is more commonly rated at half that amperage.
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