Top-down view into the bell
When the back-cap is removed you will gain access to the diaphragms, cushion, and diffuser ring. The diffuser ring is the ring in the center held in with three Allen-head bolts. This piece can be replaced if needed, but is usually okay unless bent/damaged/corroded. If you don't immediately see the diaphragm and cushion after removing the back-cap, check inside the back-cap. In most cases, the diaphragms and cushion will get stuck inside the cap and will remain attached after removing the cap. You can give the cap a light tap on a hard surface to break the diaphragms free, or use a small toothpick to pry it out.
Now that your bell has been disassembled, we can now put it back together with new diaphragms and cushion. The diaphragm cushion will be sandwiched in between the diaphragms upon re-assembly. Line up one diaphragm over the center of the bell. Place the diaphragm cushion on top of the disc, and place the last diaphragm over the cushion. The image below shows a blown up view if the assembly order.
We find that putting this together is much easier if you put the diaphragms/cushion into the back-cap first, and then re-install the back-cap to the bell.