Remove the rubber sleeve from the neck of the die grinder

Remove the 4 screws that hold the neck on

set aside the plastic coupler & large washer

While holding the neck in a vice, unscrew the collar nut

Set aside the smaller washer & felt washer that were behind the collar nut

Using the handle of the crescent wrench, unscrew the butterfly nut

Set aside the butterfly nut

Place new shaft in the neck.

Place metal washer and felt washer into neck, then reinstall collar nut.

Reinstall butterfly nut.  Note the vice is holding the shaft

Reinsert plastic coupler

Place large washer in neck

How it looks before reattaching the neck

Reattach the neck with 4 screws, be careful to line up exhaust vents to the side

Slide the rubber cover back onto the neck