So I have an 81 GS with what I believe is an 84 GSL? rear axle. I have a 3.90, lsd, and all around disc brakes and the car is on panasports. Im looking to do a brake change/upgrade soon, and I was wondering how I would go about buying rotors? Do I get front rotors for an 81 and then rears for an 84 gsl? Or can I just buy rotors for an 84 all around? I've been trying to figure this out for months and any help would be greatly appreciated. Thank you,

 

The front brake disk/hub is different between the 79-83 cars and the 84-85 cars. The rear disks were available and the same from 81-85. I assume it's all 12A suspension and not GSL-SE swapped.

MazdaTrix has all these discs available on their site. The sku #'s are:
79-83 front - 33-251B-8871-BR
84-85 front - 33-251B-FA54-BR

81-85 rear - 26-2510-FA18-BR

They also offer drilled and/or slotted rotors for all those years. You might be able to find them cheaper somewhere else, but they're available.

 

The sure way to verify is to pull an axle out and count the splines.
26 = 84-85
24 = 79-83.

 

Rear brake rotors for 12a based disc brakes (GSL,110mm pattern)) should all be the same regardless of year. GSL-SE obviously different.
Front rotors are part of the hub and you need to get the correct bearing size(large or small). 81 fronts should be small bearing.