I have chosen several posts from a couple of threads to create this "Sticky". I hope it will help people who decide to tackle the task of replacing their own diaphragms. For the record, while I have replaced many myself, I would recommend that you seriously consider having a professional factory authorized shop do the work. The money saved by your own installation is lost when you let the magnet pull your screwdriver into the new diaphragm. Going to a professional also saves you the hassle of dealing with JBL if you get an out of round diaphragm or one that simply won't fit your driver
With that disclaimer, check out these photos and comments below. These are of a small format driver, but the large format drivers are essentially the same.
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Motor innards (without diaphragm). Note the three diaphragm body screws and the very small dual locating pins. The brass part in the center is the phase plug