This is the first rebuild of the firebox since 1980. I broke the firebricks trying to get the melted clinker off them.
The first step is to remove the baffle in the front, under the doorway. It is held in place with four bolts and nuts. Remove the bolts and left the baffle up and out through the firedoor. If only wood has been used, you might be able to pull the grate and grate holder combo straight out through the ash door. It sits on angle iron supports and slides out.
If you are only renewing the grates and/or the holder, just slide everything back in again. The baffle is then re-installed and the four bolts are left slightly loose, so the iron baffle can expand and contract. The baffle sets on top of the grate holder to keep it from lifting up. I reused the clevis pins and the bar that allows both grates to rotate at the same time. The grates can sometimes lock up with clinkers between them, but I very seldom shake anyway. I use a 1/2" steel pipe to break up the bed and push out clinker that gets between the grates.
If only the firebricks need replacement, leave the grate assembly in place. You may be able to lift the bricks up and pull the bottoms out to remove them. If not, pull out the grate assembly as described above. Break them with a hammer into smaller pieces, if necessary. Behind the bricks is a fiberglass pad, about 1" thick. Use care when removing the bricks and maybe it will last another 30 years.
Try to find firebrick at a brickyard that is 1 1/4" X 4 1/2" X 9. The imported brick measures 1 3/8" thick and has to be chipped away at the top 1" to insert it behind the angle iron. Keep this in mind before you start the project. The last I knew, efm was using the imported brick. I bought firebrick at the local brickyard for $1.78 each and they are USA made.