When you put the shim in the voice coil gap, it should rest on a little ledge in there. It is very easy to push the shims past this ledge. Be careful not to do that. The shims must bottom on the ledge and you must set the voice coil so that a few layers of the windings are showing on top of the magnet plate. Also, be very very careful when cleaning the old glue on the collar of the cone throat. Sometimes it will come off easily and sometimes you have to pick it off. Also be careful when removing the old rotted foam on the wider edge where the foam surround will go. When you first put the foam on the cone it will not sit level. You must be careful to push it down under the cone until it is as level as you can get it. Glue the foam to the cone first and then play with it until you can get it level on the frame.