If you do your own rear brakes on an older Miata, you should know the following. The piston pushing on the brake pad is not the push in type. Once you take the brake assembly apart and pull the old brake pads out, you have to screw the piston back into the assembly (not push in like most cars). Just twist it in or if you don't have enough strength use channel locks. If you have any comments or recommendations let me know here. Have a great MX-5 day.

Update from a fan:

...Screwing the piston... will work but if you look directly behind the piston on the back of the caliper there is a plug and if you remove it under it is a allen screw. When you turn it that will pull the piston in much easier. That is the way it was intended to be done and you will not be as likely to tear the boot on the piston.

I haven't check that yet but it sounds great.