818 rear brake options

[PSUalum1986]

I have reached the point in my build where i need to make some decisions. I am planning on a 3.6l H6, 5 speed manual trans 818c.

My current issue is determining what brakes to go with on my future 818 build. My donor is a base model 2007 impreza with 2 pot/single pot disc brakes. I want to upgrade these to at least a WRX 4 pot/2 pot setup, with the big brake upgrade, the H6 rotor upgrade, or the wilwood options not out of the question. I have decided to go with the Wilwood pedal setup.

Would i be able to do this with my basic model hubs/spindles or would these have to be replaced also?

I am open to anyone's suggestions here.

[Hobby Racer]

I've built my 818R with similar options, EZ36R, big brakes, etc. Should help you out.

https://thefactoryfiveforum.com/showthread.php?23199-John-s-EZ36R-H6-818R-Build

[PSUalum1986]

Hobby

As i mentioned, i am seriously considering this option. I would probably go that route but my question still remains. Can this big brake upgrade be done without purchasing STi hubs and/or spindles?

I know the STi hubs are different than the base model I have, but i think the WRX ones are the same. Trying to keep this all straight is the challenge.

[flynntuna]

Yes it can be done with the WRX hubs.

[Hobby Racer]

Hobby

As i mentioned, i am seriously considering this option. I would probably go that route but my question still remains. Can this big brake upgrade be done without purchasing STi hubs and/or spindles?

I know the STi hubs are different than the base model I have, but i think the WRX ones are the same. Trying to keep this all straight is the challenge.

Yes, as stated in my build thread, I used 2006 WRX hubs / spindles which are the same as base model hubs / spindles.

[phil1734]

'06 and '07 WRX rear calipers have a wider spread on the mounting holes, not sure if the base models also received a change for those years. Rockauto makes it nice and easy to cross reference part numbers on the backing plates to confirm one way or the other.

Hubs are all the same across RS/WRX for all years.

Not sure what "big brake" upgrade you're considering but hopefully it increases the piston area of the rear calipers. That's really the root of the 818 brake issues.

[UnhipPopano]

The rear piston area of the rear caliper is only part of the problem. For a road car, you would like to retain the independent emergency/parking brake system. Then find a reasonable Front-Rear brake balance given the reduced weight, lowered center of gravity and stiffer springs. From what I can tell from what I have read, Big Brakes are referring to replacing the front brakes with those that have more stopping power. So far the only solutions presented so far is to mount the same brakes [calipers and disks] both front and back. Initial reports from this is that it was an improvement. Is it possible to use the brakes from the BRZ? It strikes me that they would be closer to what is needed.

[phil1734]

The rear piston area of the rear caliper is only part of the problem. For a road car, you would like to retain the independent emergency/parking brake system. Then find a reasonable Front-Rear brake balance given the reduced weight, lowered center of gravity and stiffer springs. From what I can tell from what I have read, Big Brakes are referring to replacing the front brakes with those that have more stopping power. So far the only solutions presented so far is to mount the same brakes [calipers and disks] both front and back. Initial reports from this is that it was an improvement. Is it possible to use the brakes from the BRZ? It strikes me that they would be closer to what is needed.

The rear calipers not having enough clamping force is all of the problem.

As supplied from the donor, the front brakes will lock way before the rears in the 818 due to the weight distribution being reversed. Factory Five "fixed" this problem by installing a prop. valve to reduce line pressure to the fronts which re-balances the brakes by making both the front and rear equally in-effective. This, in combination with deleting the booster, is what leads to the incredibly high pedal effort and reduced control during threshold braking.

As supplied, the kit keeps the functionality of the OEM parking brake system, so that's not an issue. (Most if not all states will require it's functionality for registration anyway.)

Most off the shelf big brake kits upgrade the fronts and rears together, but keep the same front to rear ratio for a WRX/STi. They aren't designed for an 818. So they'll give you more braking ability, but are still horribly mismatched front to rear. This includes the Wilwood set-up sold by FFR (it's just the WRX set-up that's widely available around the world.)

You can put the front calipers on the rear, or substitute the rear wilwood calipers for ones with larger piston area. It's a special order but at no additional cost.

Given enough time and money, you can use whatever brakes you want. While the BRZ calipers might be closer, they still won't work properly since they're designed for a car with 50/50ish weight distribution, not 40/60ish. Better than the Impreza's 60/40 but if you're going to put the effort into adapting random brakes just for the sake of it, put the impreza fronts on the rear and be done.

And yes, a few that don't track or push their car have been happy with a more aggressive rear pad compound, usually in conjunction with the "H6" rear rotor conversion.

[PSUalum1986]

Thanks for the input, especially Hobby. He provided confirmation about the base model vs WRX spindle/hub configuration. For whatever reason, i wasn't able to find that.

[prematureapex]

I'm thinking through the same thing.

So far, I'm leaning toward 05+ LGT rears (same larger H6 rotor diameter, but vented...which would be big for heat capacity on the track). That would be about a 10% bias shift rear vs. a stock WRX 2/1 setup.

I'm not sure that will be enough...

The close second place is running WRX front 2 pots or 4 pots in the rear. I think I'll have to drill a new hole in the backing plate/mounting bracket...but not much more beyond sourcing a rotor (which people on here have done). This will create a big rearward shift, perhaps too much.

With the LGT rears, I still may want to use a portioning valve to dial back the front, but with any WRX front brakes in the rear, I might need to back off on that end.

As the LGT stuff is so cheap ($150 bucks for used calipers/brackets and new rotors) and a direct bolt-on, I might try that first. Then do something more drastic is bias/heat capacity is an issue.

[Bob_n_Cincy]

The close second place is running WRX front 2 pots or 4 pots in the rear. I think I'll have to drill a new hole in the backing plate/mounting bracket...but not much more beyond sourcing a rotor (which people on here have done). This will create a big rearward shift, perhaps too much.


This is not to much. We ran 5 or 6 track days with front Impreza calipers and same pads on all 4 wheel with no PV. It was good but not perfect. At 80-100 mph the rear locked a little before the fronts. We wanted the fronts to lock a little sooner so the car would stay straight. We then add a PV to the rear circuit with it turned down just a hair.

IMHO the best set up would be square brakes with a balance bar pedal. Start tuning with it in the middle.

Just a note. My gas tank is in front. My F/R weight is 871/1210 lbs. 41.9%/58.1% This does not include drivers and passenger weight which is closer to the rear in our car.

Another note: We were running Toyo R888 235/40-17 in front and 255/40-17 rear

Here is my rear setup. https://thefactoryfiveforum.com/showthread.php?12534-MRG-MotorSports-818S-Build&p=218828&viewfull=1#post218828
Bob

[prematureapex]

This is not to much. We ran 5 or 6 track days with front Impreza calipers and same pads on all 4 wheel with no PV. It was good but not perfect. At 80-100 mph the rear locked a little before the fronts. We wanted the fronts to lock a little sooner so the car would stay straight. We then add a PV to the rear circuit with it turned down just a hair.

IMHO the best set up would be square brakes with a balance bar pedal. Start tuning with it in the middle.

Just a note. My gas tank is in front. My F/R weight is 871/1210 lbs. 41.9%/58.1% This does not include drivers and passenger weight which is closer to the rear in our car.

Another note: We were running Toyo R888 235/40-17 in front and 255/40-17 rear

Here is my rear setup. https://thefactoryfiveforum.com/showthread.php?12534-MRG-MotorSports-818S-Build&p=218828&viewfull=1#post218828
Bob

Standard GD Impreza brakes? Any way to pull something like this off without machining the rotor? I'm fine drilling the backing plate. Maybe the 4 pots would clear, but theyd need a different rotor.

Thanks!

[prematureapex]

Posted in the other thread, but you can buy thicker parking brake shoes so you can just run standard cheap sti rear rotors. I think that's what route I'll go.

[Bob_n_Cincy]

Standard GD Impreza brakes? Any way to pull something like this off without machining the rotor? I'm fine drilling the backing plate. Maybe the 4 pots would clear, but theyd need a different rotor.

Thanks!

I think my front rotors were a little bigger. They are off my donor which was a 2004 FXT.
Bob

[prematureapex]

I think my front rotors were a little bigger. They are off my donor which was a 2004 FXT.
Bob

OK, thanks. The FXT uses the WRX 2/1 setup. Question for you...

Can I mount the caliper you used to a modified rear backing plate without the need for a lathe to machine the STI rotor for clearance?

I know you used the DBA STi conversion rotor (an STI rear rotor but with a 170mm barrel for the ebrake), but I believe the OD of the hat portion is the same vs. a stock STI rear rotor.

Edit: I hope we're talking about the same thing here...

My understanding is that you put FXT/WRX front 2-pots on a modified rear knuckle backing plate, and used the STI conversion rotor.

I'm hoping to do the same thing, albeit with a cheap standard STI rotor and 10mm thicker ebrake shoes.

[prematureapex]

Sorry for all the posts...

Has anyone considered the 05+ LGT rear vented rotor over the STI rotor? It's 290mm and 18mm thick. That's not too far off the 294x24 of the WRX/FXT front rotor. It would avoid the ebrake problems.

I wonder if caliper mounting would be harder or easier with the smaller rotor. The hat is probably small in diameter, so maybe there would be no issue with rotor to caliper interference.

As luck would have it, there's an 05 LGT in my brother's driveway...I'll play around this week.

[Scargo]

I would look at Girodisc rear rotors. Have worked great for me in my STi race car.
I spent the big bucks for custom designed (by Stoptech engineers) Stoptech brake setup and Tilton pedal box for my R. Brakes are so important and I've got a ton of brake.

[Bob_n_Cincy]

OK, thanks. The FXT uses the WRX 2/1 setup. Question for you...
Can I mount the caliper you used to a modified rear backing plate without the need for a lathe to machine the STI rotor for clearance? Not really
I know you used the DBA STi conversion rotor (an STI rear rotor but with a 170mm barrel for the ebrake), but I believe the OD of the hat portion is the same vs. a stock STI rear rotor. I don't know
Edit: I hope we're talking about the same thing here...
My understanding is that you put FXT/WRX front 2-pots on a modified rear knuckle backing plate, and used the STI conversion rotor.
I'm hoping to do the same thing, albeit with a cheap standard STI rotor and 10mm thicker ebrake shoes. The fxt front caliper requires a smaller hat


Sorry for all the posts.. Has anyone considered the 05+ LGT rear vented rotor over the STI rotor? It's 290mm and 18mm thick. That's not too far off the 294x24 of the WRX/FXT front rotor. It would avoid the ebrake problems.
I wonder if caliper mounting would be harder or easier with the smaller rotor. The hat is probably small in diameter, so maybe there would be no issue with rotor to caliper interference.
As luck would have it, there's an 05 LGT in my brother's driveway...I'll play around this week.

prematureapex,
My first attempt a brake modification was with the LGT rotor.

101733

No machining was necessary. Because of the thinner rotor, I had to increase the thickness of one of the pad backing plates by 0.25"
It also had the problem of not using the whole pad. The top 3/8" of the pad was not touching the rotor.

Then I switched to the DBA rotor. with the hat outside diameter turned down. This fixed the thickness and diameter issue.

101734

Summit has these rotors https://www.summitracing.com/parts/dba-dba2657s

[prematureapex]

Thanks! That saves me time trying the LGT option.

About how much did you have to turn off the rotor? Think I could mill the same off the bracket instead? (And maybe I don't even need that portion of the bracket at all...).

Edit:

I found the drawings of both your conversion rotors and the stock 04 STI rear. I see no reason we can't do this with regular STi rear rotors ($40/per) and $100 in ebrake thicker ebrake shoes.

I'm going to pull the trigger and report back.

[Bob_n_Cincy]

Thanks! That saves me time trying the LGT option.

About how much did you have to turn off the rotor? Think I could mill the same off the bracket instead? (And maybe I don't even need that portion of the bracket at all...).
Edit:
I found the drawings of both your conversion rotors and the stock 04 STI rear. I see no reason we can't do this with regular STi rear rotors ($40/per) and $100 in ebrake thicker ebrake shoes.
I'm going to pull the trigger and report back.

I think I took off about 3/8", I will have to measure the new diameter the next time I take off the wheel.
Here is the DBA drawing. .101750
Can you post the STI Drawing?
Where did you get the thicker pads from?
Bob

[prematureapex]

Sorry for the delay...

godspeed brakes in the UK sells the shoes. After expensive shipping, it wound up being a little under $200. I suppose this route is only really worth it if you go through rear rotors (which I'd imagine you would tracking the car).

https://www.godspeedbrakes.co.uk/rear-brembo-adapter-kits-/72-rear-sti-brembo-fitting-kit.html

Here's the stock rear STI rotor.

101807

Now that I'm looking at it, the stock STI rotors certainly don't have the barrel thickness to turn nearly that much off.

So my options would be 4-pots in the rear (have been done before without touching the hat IIRC)...or grinding down/removing that portion of the caliper bracket.

BTW: What do you think the purpose of that lower caliper bracket loop is? Just a back-up catch for the pads should they come free? I wouldn't think any stiffness it adds to the bracket matters that much considering where they are bolted in...but I could be wrong.

[prematureapex]

Edit...

[Bob_n_Cincy]

BTW: What do you think the purpose of that lower caliper bracket loop is? Just a back-up catch for the pads should they come free? I wouldn't think any stiffness it adds to the bracket matters that much considering where they are bolted in...but I could be wrong.

I thought about cutting the bottom loop of the caliper bracket. I was worried that this would hurt the integrity of the bracket, so I did NOT do it.
Bob

Here is a chart of calipers with "elective cylinder diameters'"
https://thefactoryfiveforum.com/attachment.php?attachmentid=42944&d=1435013249

[prematureapex]

What are you doing about pad overhang? Or at least I think there's a few mm of less radial depth on the STI rotor vs. the FXT/WRX pad. Or is the whole pad on the rotor?

[Bob_n_Cincy]

What are you doing about pad overhang? Or at least I think there's a few mm of less radial depth on the STI rotor vs. the FXT/WRX pad. Or is the whole pad on the rotor? I believe the whole pad is on the rotor.

[DodgyTim]

I am using a set of these on a buggy build using Subaru rear rotors etc. 101868
Wilwood 4 pot calipers with integral handbrake mechanism.
They aren't listed in the Wilwood website but are available.
The good thing about having the handbrake in the caliper is it allows running plain (i.e.front) rotors, so there are more options available. Part number for mine are (with pads) Wilwood 120-6805 (F) 120-13517 (R )
About $700 for the pair with pads.
Way lighter than the 4 pot Subaru rears I have on my 818 too