What rear calipers will fit a 5 lug FC?
 

If you have the 5 lug hubs, the rear brake caliper pistons have to be unscrewed. You can use the official tool from Mazda, a set of needle nose pushed into the dimples on the face of the piston, or a set of round vise-grips to grasp around the top part of the piston (above the little valley) and twist counter-clockwise. If you've already tried that, and you're really sure it wont come apart, I would just go to local parts stores and buy rebuilt calipers and trade yours in as cores.

4 Lug brakes won't fit, as the 4 lug rears are only solid rotors and not vented. It won't clear the 5 lug rotor.

EDIT: And if local parts stores don't have anything, try Rockauto and just make sure to read the description of the calipers to ensure they're for the 5 lug cars

As WonderousBread has stated, the rear caliper pistons need to be unscrewed. There's a tool that makes removal of these pistons easy. It called a rear disc brake cube and can be bought at any auto parts store (https://www.autozone.com/test-scan-a...-tool/2363_0_0).

Alternatively, you can just buy a rebuilt left rear caliper at any auto parts store. Rockauto sells them for about $100 including $30 refundable core charge (https://www.rockauto.com/en/moreinfo.php?pk=521993&cc=1192395&jsn=457). If you buy from Rockauto, than make sure the part matches your original part. I've had problems with Rockauto mis-boxing parts (i.e., wrong part in box with right part number).

I have the tool, I tried getting the piston out but you'll just have to take my word for it when I say it's too ****ed to bother with. I've looked through the rockauto/autozone/whatever catalogs and all of the rear left 5 lug calipers seem to be out of stock. There are some others out there, but there's no indication of whether they're for 4 lug or 5 lug Rx7s. Is there an easier way to tell? How specific are the calipers of an Rx7, will calipers from another car fit?

This seems like my best bet for one that's in stock. But is it 4 lug or 5 lug??
https://www.autozone.com/brakes-and-...2145_2362_3765

Yeah, that caliper will fit your car. To make it easier for you, just look for a rear caliper for an 89-91 RX7. They're all 5 lug and all the same.

You might want to checkout NAPA too. They seem to have stuff in stock while other auto parts stores don't.

they aren't the 89-91's still have a vented/non vented rear rotor, same as the S4, its just 5 lug.

actually that is an option too, you could do what Mazda did and upgrade to 5 lug, and keep the 4 lug caliper and just run the non vented 5 lug rear rotor

True, but the solid rear rotor is much harder to find than the vented one.
That's the only reason I swapped to the "turbo" rear set up...I couldn't get solid rotors anywhere reasonable.

>>> ...89-91's still have a vented/non vented rear rotor...
Ok, you are correct.

>>> ...upgrade to 5 lug, and keep the 4 lug caliper and just run the non vented 5 lug rear rotor.
From an earlier post, it's my understanding that S5 non-vented rotors are hard to find.

The p/n that he listed was rear caliper for 5 lug vented rotor. So, I assumed that he has rear vented rotors. If that's the case, than to make it easier he could just search for a rear caliper for either an S4 or S5 TII.

thats because the US is the only place in the world that got the small brakes...

Oh, I don't know..."small brakes' is kind of a misnomer.
In every respect save the width, the brakes are identical.

The one I linked earlier is apparently out of stock. A couple websites say this one fits my 1987 GXL, but rockauto lists it as a 4 lug caliper. It has the same part number as the one earlier, does that mean it's also actually for a 5 lug? How can I tell if it fits or not? Does anyone know? https://www.summitracing.com/parts/a...zda/model/rx-7

Unless I'm incorrect, "small" refers to the fact that the front brakes are the 4 piston calipers and larger discs when paired with vented rears, whereas single piston front and smaller discs were paired with the non-vented rear discs. The rear rotors are always the same size, but the non-vented rears were only offered with the "small" front rotors.

Okay, this is definitely the wrong size. I should have trusted the 4-lug description. I'm going to see if a brake shop can rebuild my caliper for me, but I might need a new piston.

The caliper is the same between solid and vented rear rotors. Only the bracket changes. It used to be the cheap way to upgrade solid and vented rears, order the vented stuff and return the solid stuff. Now on S4, anything that is turbo, vert, GXL,, AAS, or heavy duty suspension will get the correct caliper and bracket.