When the time comes that you feel like repacking your muffler, here are the simple steps to follow.
1. Remove muffler from vehicle if possible. This usually makes the muffler easier to work with.
2. Clean any dirt, oil, debris off of the allen bolts holding the outer case to the end cap.
3. Using an allen key that is in good shape (sharp corners, not rounded off) remove the allen bolts. If you find that they are stuck you may try and heat up the bolts and remove while hot. A light tap on the bolt can also help. This may be more common with the old style mufflers, but should not be an issue with any of the new style. Be certain to apply pressure on the tool keeping it firmly inside the head of the bolt. Do not let it slip out!
4. After removing all three allen bolts, slide the end cap out of the case. If you have an old style muffler the core will come out with the end cap.
5. Pull on the perforated core and the core + packing should come out.
6. Inspect your old packing if you wish, then dispose.
7. Your new glasmat will probably need to be cut to fit. The replacement size for your muffler may be found here.
Wrap either the glasmat or the scrubble snug around the perforated core. You can use masking tape or similar tape to hold the glasmat in place around the core, or even safety wire if you wish. For the scrubble a safety wire or similar material is recommended.
8. Re-insert the perforated core with new packing into the case, ensuring the core fits properly at the outlet (between the tapered cone and the outlet). Line up the slits in the core with the three holes in the case.
9. Install the inlet end cap over the core, lining up the threaded inserts with the slots in the core, and the holes in the case.
10. Check alignment of the holes again, and begin to install the allen bolts. Install loosely until all three of the bolts can be installed, then tighten until hand tight.
11. Admire your muffler one last time before re-installing on the vehicle.
12. Your muffler is now ready to perform like brand new.