Off season time, And while i have a few projects going on my 1st gen. I have spent a few hours looking into BB for it. And think i may have found a unknown/ known but not posted way to get a bigger brake on the rear of a non se car. Starting with a 1990 Mazda 929 rotor 5x114.3 version It is a 266mm disk 18mm vented rotor. Paired with a ( in my case) 04 rx8 rear caliper witch is for a 18mm vented rotor but a massive 302mm diameter rotor. And where im planing on staying with a 15" wheel the 266 should be clear no issue.

Now for all the specs:
unsure if 79-85 non se are the same caliper But
Piston bore 34.925mm
10mm non vented disk
236mm diameter
total height 72mm
4x110 pcd

1990 Mazda 929:
18mm vented disk
266mm diameter
total height 58mm
5x114.3 pcd

2004 Mazda Rx-8
Pistion bore 43mm
18mm vented disk
302mm diameter
total height 44.2mm
5x114.3

Now For a rough estimate (I plugged the numbers into ai)+84% more brake torque.

clamp force ∝ piston area, and brake torque ∝ clamp force × effective radius
Torque ratio≈(43{squared})×(266)(34{squared})×(232)=1.83S o the RX-8 43 mm caliper on a 266 mm rotor gives ~1.84× the torque of your stock 34 mm caliper on a 232 mm rotor—i.e., ~84% increase.
Pads will play a part and a few other variables i know but this is promising in my book. So i fired up my Cad software and tossed in some numbers to just visualize the differences

Gsl stuff on the left and 929 stuff on the right. Both in the order of Hub bore-Lug pcd- and OD of disk. So there will defiantly be a need for a hub concentric ring.

. both "rotors" with the mounting flange in the same plane. I dont know the thickness of the face of each yet but will pull a disk off my car tomorrow to measure it up. And will half to buy a disk for the 929 to get the info. But this gets a quick reference as to where the new disk will sit on the axle flange.

Now i know there have been a few who have converted to the fc rear brakes and as a visual the rx8 caliper looks fairly similar to a fc calipers.


rx8

rx7 FC

Tomorrow i will head out to my bone yard of cars and pull the calipers off the rx8 to bring home and start to mock up a fitment on a spare axle. The good news is I have a spare drum Axel and disk so who knows, if this all works out and can be lazer cut i can offer a bracket for both.
I also need to figure out if there is a difference between drum/disk flange to flange. I know they are both 24 spline, thankfully so i can swap my 4.77 ratio into witch ever unit I build. Ill get back with some more answers as soon as i get some more parts in front of me on the bench.

 

Got the rear axle (drum) version. axle shafts from disc to drum both measure just under 28 inch, so I'm going to say they are the same. Fought like hell getting the calipers off the 8 but i have em now.



the next set of pictures are of the 8 calipers with pads loaded in on a t2 front rotor that is 22mm thick!



And yeah 22mm is to much, while I can get the rotor to rotate pretty easy looking at the last pic you can see the rotor is right on the bracket. And i did get a caliper to bolt on and spin the rotor. That kinda changes my approach a bit as everywhere i looked or read, I was told a 22mm rotor wouldn't even fit down past the pads. And umm well yes they do. Clearly they are used pads but fitting down in between the bracket was a big supersize. So I'm on the hunt for a 20mm rotor that meets the rest of my criteria. And what is that you ask well time to fire up the pc and do some cad.


I didint find it necessary to model the whole axle so i just made the flange (lavender part) then the axle shaft (dark blue) and gave it the correct offset from the face to flange without a baking plate. The rotor is that from a 96 miata, Luckily i found brembo makes that rotor and give full blown blueprints of the rotor. Didint go to crazy but just enough for the important measurements. then we have the actual bracket in the light blue that will double as my bearing retainer. The bracket is 3/8 and we can see where that lines up by the rotor. So a few ways to go about this. Make a spacer between the axle shaft and rotor or find a different rotor all together. And no i didint forget about the 929 rotor, I got about half way thru making it and the program crashed. but i will do the same when i get it done and put it next to the "axle" model.

oddly enough i found this rotor on brembo's site



The better part is it is a very low offset so that 3/8 caliper bracket can play nice or go to a thicker bracket to get the caliper located correctly. It is for a Citroen xsara Picasso N68 what ever that is. But can be found on amazon or various retailers on the web. And most of this will need a re drill for pcd but you half to do what you half to do right. Ill play around with models and see what i like best. I just have a feeling im going to model a caliper and am not looking forward to that.

 

I think we found a winner!
3/8 bracket
1/2 bracket


I will 3d print the rotor and bracket to test fit it all before anything. Because i do see the issue of the caliper hitting the rear wheel due to the small offset of the rotor. But I'm getting somewhere I can feel it . And if need be a spacer up front could help this issue. ill get it printing up so i can locate the caliper properly and mock it all up on a rear end.

 

So got a few parts printed and mocked up on the axel. I need to learn how to measure properly or subtract when I add haha. Any ways that should be fixed but hear we are. All bolt on 266mm vented disk for the rear. 2nd pic is a 20mm rotor blank just for the pad area. And fits perfectly in there. And the wheel is a american raceing ar907 15x7 +22. Im going to print a full diameter rotor and a new bracket with the correct caliper offset this time and do a full mockup to re test with these wheels and my Konig rewinds in 15x7 forget the off set but will figure it out by the next post.







in the

 

T3 Wilwood kit works amazing.... FYI

 

There kit is for gsl-se. And finding se parts is ridiculous. Im working on non se axels so everyone can have access to this.

 

Progress is moving, Ive now printed out 5 brackets and the current one should be the last for fine tuning adjustment. Ill know before the days end. But for the fronts i did make a drill temple to convert the 5x114.3 fc rotor to a 4 lug turned out pretty perfect. Now i can drill and get the spindles on the car with the tII front calipers.




I also have one made to convert the rear axel shafts to 4x100 so i can run the same set of wheels front and rear.

 

Well hear it is

4 pots up front





And hear are the rewinds mounted on the axle with still a dummy rotor but using the rx8 caliper. Every thing lines up and fits perfect. But finding the Citroen disk in the us is becoming a hand full. and being a 2 week delivery is also a killer But none the less i have ordered the rotors and sent off for the bracket to be water cut. next update will be all in metal!

 

It all works! I knew it would be close from my 3d prints, but now i know for sure. I do need a 1mm spacer from axle flange to rotor but it is all right there. Im taking my axles over to a buddy so we can press off the bearings, install my flange and press new bearings on today. I guess now i better jump on getting the axle cleaned up and painted. And of course redrill to 4x110 on the rotor. But i still have some time before i can even take the car out.

 

They have it for GSL now

 

73rx3 I found what you where referring to don't know why I struggled with finding it. But 1600 is steep, not really but I just about have my rear axle done. Just working on getting the right diff pattern down. And while yes i get it, its willwoods ect. I am at 250 us into my setup, yeah its not fancy billet. But it is all oem parts, still will be a big upgrade from the tiny solid disk paired with the t2 fronts. And even better rock auto has all my parts . Im still in the "racing" on a budget. if we can call it racing....