EvoX rear caliper swap

[etc]

This is designed as a complement to the ATS front caliper swap: http://www.ft86club.com/forums/showt...68#post2628568

This should resolve any brake bias concerns. It will match the four front 42mm pistons with two rear 40mm. Here are the calculations used to arrive at this pairing: https://docs.google.com/document/d/1...it?usp=sharing

But more convincing to many will be that this is what the '17 BRZ Brembos are 4x42 front 2x40 rear with STI sized rotors, source: http://www.ft86club.com/forums/showp...3&postcount=12

These are matched with DBA's 4000 series STI rear rotor for 08+ sti. So with the front brakes it is easier you can use the 04 sti rotor to get our bolt pattern, rears are complicated by a change in disk offset in 08, so 04 rotors wont work, source: https://forums.nasioc.com/forums/sho....php?t=1265631 However DBA drills their rotors for both 5x100 and 5x114 so you can use their 08+ sti rotor. I think you should be able to use the BRZ pp rotors since they are probably the same as the STI rotors but with the our pattern, as those become more available we can see.

Surprisingly the evox's calipers line up perfectly for the mounting bolts. However, as with the ATS calipers, you need to drill the factory mount holes out to 12mm (from 10mm).

You will then need to remove the rear dust/gravel shield as with most BBKs. I followed instructions on this site in reference to another BBK and just cut the shield off instead of removing the drum brake and the hub in order to properly remove it. To cut it off I used a carbide blade on an oscillating tool that made the job pretty easy.

You will also need to space the caliper out 4mm to center the rotor in the caliper. To do this I designed some spacers, essentially large washers maximizing contact points between the calipers and the hub. I had these waterjet cut by bigbluesaw.com, using their 6061-T6 aluminum at 0.16in thickness. I have attached the .dxf file needed for cutting to this post (in the zip file). The downside is that their pricing only makes sense at 50 of them cut. So I have eleven extra sets I can ship to people for $20 shipped (pm me), after that you will need to get a set cut yourself and pawn off the extras.




You will also need longer 12mm bolts than those that come with the evox calipers since you are spacing them. I found the sti bolts (part# 901120103) to be the right size M12x1.5x37long and they are the proper class 10 bolts.

With all this said there is one minor downside, the pad will actually hang 5mm off the outside of the rotor. My pads, carbotech xp8s, are 9.9mm and the rotor is 20mm thick so even if I went to the metal on both pads they still wouldn't touch, yes you are wasting some pad but it is in the rear and in my experience these last a long long time so I am not so worried but be warned.


So total price looks like:
two evox rear calipers from ebay: $240
two 08 sti dba4000 rear rotors: $270
four spacers: $20 from me, $9/set if you buy 12 sets from bigbluesaw
four sti bolts: $12 + shipping

That about covers it, I am happy with the result. Hope this helps others.

[all4spl]

Hmm Have you looked into the Evo 8 rear calipers? Apparently they are slightly smaller so that may fix the pad overhang?

[jamal]

08+ STI rear brembos line up right and bolt on.

Although I think they have 36mm pistons which is not ideal.

edit: no, 08+ sti brembos have 40mm pistons which is a much better match to the front brembos.

[etc]

Interesting idea, looking around evo8 looks to be around 300mm and evox appears to be 330mm so assuming the mounting points are the same that is a 30mm drop which is too much, we would want to drop 5-8mm maybe.

[etc]

In regards to the sti brembos, I am mostly interested in shifting brake bias rearward so that wouldn't work as well for me, if the goal is looks then that would be an easier route. (Not that I don't love the looks too)

[all4spl]

Gotcha. Maybe we can find a disc that is slightly bigger or something then for the 5mm. im sure the 5mm overhang is effecting braking slightly.

[surfwaxsmitty]

Thanks for pursuing this and sharing the info!

Looking forward to seeing how this setup evolves.

[etc]

I will update when I have put some track time on these, I am in the middle of moving though so I don't plan on hitting the track again until maybe mid june.

As for a larger disc, that would be great but options are limited. Rears are complicated by needing to match parking brake drum diameter as well as bolt pattern and offset. The best bet if you wanted to try to get a couple more mm would be to find a two piece rotor for the sti and using the properly sized hat you could try to find some replacement discs that are a little larger. There is a bit of standardization in those discs so it should be possible.

Personally I am happy with it so far and don't have much motivation to continue refining it but welcome others to build on it. If I do anything else it would be to consider pushing bias farther rearward than stock with maybe a four piston rear but I doubt I will actually peruse it.

The effects on braking are actually more rearward bias than the calculations show because you are exerting the same force just farther out from the hub. Other than that higher brake pad wear because that same force now has (5*87)mm less area to wear. I am not too concerned about the wear because rear pads wear slowly enough to not be a meaningful expense to me.

[ajc209]

Originally Posted by etc

I will update when I have put some track time on these, I am in the middle of moving though so I don't plan on hitting the track again until maybe mid june.

As for a larger disc, that would be great but options are limited. Rears are complicated by needing to match parking brake drum diameter as well as bolt pattern and offset. The best bet if you wanted to try to get a couple more mm would be to find a two piece rotor for the sti and using the properly sized hat you could try to find some replacement discs that are a little larger. There is a bit of standardization in those discs so it should be possible.

Personally I am happy with it so far and don't have much motivation to continue refining it but welcome others to build on it. If I do anything else it would be to consider pushing bias farther rearward than stock with maybe a four piston rear but I doubt I will actually peruse it.

The effects on braking are actually more rearward bias than the calculations show because you are exerting the same force just farther out from the hub. Other than that higher brake pad wear because that same force now has (5*87)mm less area to wear. I am not too concerned about the wear because rear pads wear slowly enough to not be a meaningful expense to me.

have you been on track yet?

[etc]

I was out at Thunderhill yesterday. Worked great, no issues.

Braking is significantly better for me but I also upgraded my front pads (ebc yellow -> carbotech xp8). But with this setup now and xp8s all around the braking is really solid, dependable and hard. I can trigger ABS on 235 nt01s if I push it. It feels well balanced in braking, particularly in trail braking now. Not much else to say, shit just works, I am very happy with it.

Ideally I would have some instrumented tests with before and after 100-0, braking gs, etc.. but that sounds like work and this is just a hobby.

[SkAsphalt]

Originally Posted by jamal

08+ STI rear brembos line up right and bolt on.

Although I think they have 36mm pistons which is not ideal.

Pretty sure 04 and up line up and bolt on..

I forgot tho, I have front STI brembos on my car, never bothered with the rears. Maybe one day for looks

[vijay.dy06]

Pmed you about the spacers

[Skeneypoo]

Originally Posted by etc

With all this said there is one minor downside, the pad will actually hang 5mm off the outside of the rotor. My pads, carbotech xp8s, are 9.9mm and the rotor is 20mm thick so even if I went to the metal on both pads they still wouldn't touch, yes you are wasting some pad but it is in the rear and in my experience these last a long long time so I am not so worried but be warned.

Hey, I'm about to purchase the parts for the front and rear upgrades.

On the rear rotors, if I just slotted the holes on the mount for the calipers about 5mm, allowing the caliper to sit lower on the disk, would I have any other issues with clearance?

Aka, is there anything else in the way stopping the caliper from dropping 5mm or does it just mount a bit too high?

Thanks man, you the brake king.

[15limited]

Originally Posted by etc

I was out at Thunderhill yesterday. Worked great, no issues.

Braking is significantly better for me but I also upgraded my front pads (ebc yellow -> carbotech xp8). But with this setup now and xp8s all around the braking is really solid, dependable and hard. I can trigger ABS on 235 nt01s if I push it. It feels well balanced in braking, particularly in trail braking now. Not much else to say, shit just works, I am very happy with it.



Ideally I would have some instrumented tests with before and after 100-0, braking gs, etc.. but that sounds like work and this is just a hobby.

Anybody have luck finding rotors to eat up the extra pad hangoff? I'm having a hell of a time even finding 08+ sti hat offset to put on a slightly larger disk.