Subaru 4 pot front callipers on the front and the rear?

[DodgyTim]

Hi
I thought I’d run a brake upgrade idea past you all for comments
I have an 818R and I’m looking at cheap option to upgrade the brakes
I’m not against the Wilwood kits, but if I buy one I’ll double the cost of the kit due to my wife’s revenge spending on shoes:eek:

My build is using the 2006 WRX brakes at the moment, so
Front = 295 dia x 25 thick rotors with the 4 pot Subaru callipers
Rear = 290 dia x 18 thick rotors with the 2 pot Subaru callipers

What I’m thinking of doing is upgrading the rear rotors with a DBA rotor part number DBA 42657 and fitting another set of Subaru 4 pot callipers to the rear (if possible).
I already have the spare callipers, kindly donated by another 818 builder who purchased the full Wilwood kit

The DBA 42657 is 316mm diameter and 20 mm thick. It keeps the standard 170mm dia handbrake.

This rear 4 pot & larger rotor combo would provide 2.4 times more rear braking than the 2006 2 pots, and the total braking would be rear biased by about 7%.

That sounded like too much rear brake, until I looked at the FFR offered Wilwood kit.

The lower cost version of the wilwood kit has front and rear 4 pot callipers, with 12” front rotors and 12.19” rear rotors. Provided the front and rear callipers are the same, this is 2% rear brake bias.

Thoughts?

[Mechie3]

Bob n cincy did this or something similar.

[longislandwrx]

I was originally going to run small lightweight brakes in the back until I heard that people were having to dial down the front brakes to get more rear bias.

If you are going to go with the 42657's instead of messing with a custom adapter why not get the rear Brembo calipers to match... I bet you could trade/sell your spare fronts and existing rears and buy some Sti takeoffs and the already made adapters
for not much out of pocket. just a thought.

[Mitch Wright]

Tim,
My original plan was to do the same thing but I was going to run the front rotors on the rear (I deleted the e-brake on my R build)
I have ended up going another direction and running the same AP calipers and 299mm rotors front and rear. With 57% rear weight and bigger rear tires is the logic I am using.

[Bob_n_Cincy]

Be careful when you talk about 2 pot, 4 pot, 6 pot calipers.
The effective diameter of the pots and rotor diameter is what is important.
I am running 2 pot 3.37" in the front and rear.

The 06 2 pot impreza front is 3.37"
the 06 4 pot WRX has 3.082" front
The 06 4 pot STI has 3.386 in the front.

The 06 1 pot impreza has 1.5" in the rear.
the 06 2 pot WRX has 1.5" in the rear
The 06 2 pot STI has 1.417 in the rear.

I have more than twice the clamping force as the wrx or sti rear brakes.
With no portioning valve and square tires, my rears lock up just before my fronts. (this is a bad thing)
I am installing my wider rear tires and will test again. If problem remains the I will add proportion valve on rears.

42944

42945

Bob

[Frank818]

The lower cost version of the wilwood kit has front and rear 4 pot callipers, with 12” front rotors and 12.19” rear rotors. Provided the front and rear callipers are the same, this is 2% rear brake bias.

They are not. The rears are smaller on that Wilwood kit. And I am unsure if you can fit the front calipers over the rear discs or if you need same front 12" fitted in the back.

I am curious to see how you end up with anything (logic driving you to choose one thing over another) and what will be the results.

[Scargo]

DBA's are heavy rotors. Don't know about Wilwoods. I like the idea of the same Suabru four pots front and rear. I just think you need some two-piece Gyrodisc rotors, or similar.

[DodgyTim]

Be careful when you talk about 2 pot, 4 pot, 6 pot calipers.
The effective diameter of the pots and rotor diameter is what is important.
I am running 2 pot 3.37" in the front and rear.

The 06 2 pot impreza front is 3.37"
the 06 4 pot WRX has 3.082" front
The 06 4 pot STI has 3.386 in the front.

The 06 1 pot impreza has 1.5" in the rear.
the 06 2 pot WRX has 1.5" in the rear
The 06 2 pot STI has 1.417 in the rear.

I have more than twice the clamping force as the wrx or sti rear brakes.
With no portioning valve and square tires, my rears lock up just before my fronts. (this is a bad thing)
I am installing my wider rear tires and will test again. It problem remains the I will add proportion valve on rears.


Thanks Bob, this is my math, but it needs to be checked:D

The 2006 wrx front calliper has a working piston area of 3.97 square inches (2 pistons at 1.591 inch diameter)
The 2006 wrx rear calliper has a working piston area of 1.77 square inches (1 piston at 1.5 inch diameter),
so for the same brake line pressure, putting front callipers on the rear disk will give (3.97/1.77) 2.25x more rear braking.
Then with the larger rear rotor (316mm vs the standard 290) that 2.25x clamping force acts on a 1.08 times longer arm, so I get the 2.4x (ish) increase in rear brake


They are not. The rears are smaller on that Wilwood kit. And I am unsure if you can fit the front calipers over the rear discs or if you need same front 12" fitted in the back
Thanks Frank, I haven't checked to see if the front callipers will fit without major modifications
One big difference is the rotor width, the front calliper expects to see a 24 or 25mm thick rotor, but the standard rear rotor is only 18mm thick. This is one of the reasons I was looking to the DBA 42657 rotor, it is 20mm thick.


DBA's are heavy rotors. Don't know about Wilwoods. I like the idea of the same Suabru four pots front and rear. I just think you need some two-piece Gyrodisc rotors, or similar
I might look at this later on, when I have more cash available, and time in the car to work out what is the best spend for performance
The DBA's are about $350 Aussie for each pair, so $700 total delivered
The Girodisc's look to be about $700 US per pair, so with the lousy Aussie exchange rate = $1750 Aussie + delivery:(

[Bob_n_Cincy]

Thanks Bob, this is my math, but it needs to be checked:D

The 2006 wrx front calliper has a working piston area of 3.97 square inches (2 pistons at 1.591 inch diameter)
The 2006 wrx rear calliper has a working piston area of 1.77 square inches (1 piston at 1.5 inch diameter),
so for the same brake line pressure, putting front callipers on the rear disk will give (3.97/1.77) 2.25x more rear braking.
Then with the larger rear rotor (316mm vs the standard 290) that 2.25x clamping force acts on a 1.08 times longer arm, so I get the 2.4x (ish) increase in rear brake


Thanks Frank, I haven't checked to see if the front callipers will fit without major modifications
One big difference is the rotor width, the front calliper expects to see a 24 or 25mm thick rotor, but the standard rear rotor is only 18mm thick. This is one of the reasons I was looking to the DBA 42657 rotor, it is 20mm thick.

Hi Tim
To solve the 18mm to 25mm thick rotor, I welded an old backing plate (1/4") to the backing plate of the outside pad.

Here are some of the trimming I had to do to make things fit .
42959

42960
Bob

[DodgyTim]

Bob, if the pad surface wears down to very little thickness, do you think it could come out of the calliper housing? or does your welded on piece act to keep it anchored?

[Bob_n_Cincy]

Bob, if the pad surface wears down to very little thickness, do you think it could come out of the calliper housing? or does your welded on piece act to keep it anchored?
That is exactly why I did it. With the pad material gone. It cannot come out of the bracket.
Also without this mod, the piston may come to far out of the caliper.
Below, you can see why I put it on the outside pad.

I wish the rotor as about an inch bigger in diameter.
Bob

42964

[metalmaker12]

The brakes you have are way more than enough

[Junty]

Hey Tim, I have previously suggested exactly your plan above - Bob also commented prior to completing his work also. My logic - not as mathematical as yours, is many other mid or rear engined sports cars with 50:50 weight bias have same from and rear callipers and rotors... My 818S has your stock standard setup, and has now completed full compliance and certification. So my next step is to improve brake performance, and I intend fitting the same 4 pot Subaru callipers from front to the rear of my car.
The only question I now have - previously I also looked at fitting these with the same 316mm Brembo rotors (standard handbrake), is what Bob has mentioned regarding the total brake force applied from the sliding Subaru 2 pot fronts versus the 4 pot fronts? 3.37 versus 3.08? This could actually make the bias/balance perfect by fitting the bigger 2 pots to the front and adding the smaller Subaru 4 pot to the rear with the Brembo 316mm rotors????
Does anyone know if any force/pressure is lost or compromised by the sliding action of the NA 2 pot front system? Why would Subaru increase to 4 pot with smaller force/area for the high spec vehicle? Is it merely cosmetic when you look through the 17inch wheels to see 4 pots?
Note - my 818S has a functioning Subaru ABS system, but I definitely require significant improvement in braking ability. My R888's grip very well, and ABS doesn't actuate, but the car certainly needs to slow a lot better than it currently does.... Even though I don't actuate the ABS, the weight certainly tips the car forward, significant weight transfer to front - I want to feel the rear pull up harder, forcing the rear to squat.

[Bob_n_Cincy]

The brakes you have are way more than enough

Hi Metal,
I agree the oem brakes are plenty for the 1800 lbs 818.
But when most, if not all, decided to go without the booster, the braking was reduced by a factor of 6.
See chart below.

By moving the hole in the brake pedal arm increased the braking pressure by 30% (I guessed at this number)
So the total braking force is about 1/4 the original boosted car with the same pedal pressure.
It is even less than that if you put a proportioning valve in the front wheels.
I increased the total braking force by 33% by my rear calipers mod.
Bob





43028

[Tamra]

We are happy with our 2 pot and 1 pot calipers with EBC Yellow Stuff pads for autocross duty, both in terms of pedal effort and stopping ability. The car stops on a dime and we have to be conscious of not using the brakes too hard, as we can easily lock up the brakes. We adjusted the bias rearward and have the car braking fairly balanced now.

Keep in mind it takes quite a bit of effort to properly bed in brake pads. They don't work well initially (I had to stand on the brakes and I still couldn't lock them up at first), especially since the brakes are manual. We bedded in our EBC Yellow Stuff pads in at an autocross school where we got a combined 60 minutes of race time. It took over half of the school before they really started working. Now they work great and I have to be conscious of how much pedal I use, else they will lock up.

To be honest, I can't see why anyone would need "more" brake on the 818. OEM calipers with upgraded pads (if you are going to be performance driving) is more than enough in our experience. If you want lighter weight, by all means upgrade - we might in the future.

For those who have upgraded, why do you think you needed bigger brakes? Did you give the OEM pads a try at all (and if you did, did you get them actually bedded in?)? I could see perhaps for real race use, needing more cooling and/or surface area.

[DodgyTim]

Hi Junty

I'm no guru on this stuff, so others may want to chime in too...:D

I'm working on calliper piston area, where Bob seems to be working on diameter. I'm not sure which is correct:(


The only question I now have - previously I also looked at fitting these with the same 316mm Brembo rotors (standard handbrake), is what Bob has mentioned regarding the total brake force applied from the sliding Subaru 2 pot fronts versus the 4 pot fronts? 3.37 versus 3.08? This could actually make the bias/balance perfect by fitting the bigger 2 pots to the front and adding the smaller Subaru 4 pot to the rear with the Brembo 316mm rotors????
From Bob's chart, for the same brake line pressure, the floating calliper 2 pots will give more brake force than the fixed 4 pots. If you work on diameters it is +6%, if you work on area it is +12%

So for the system you propose ( I think) is
Front - floating Subaru two pot callipers (from the standard impreza) fitted on the WRX front rotors (294mm OD but 255mm effective)
Rear - fixed Subaru 4 pots (ex 2006 fronts) on the DBA rear rotors (316mm OD but 266mm effective (guessed :rolleyes:)
This gives a 7% front biased system

Apart from the rotor thickness issues, there is also the pad shape to consider. The 4 pots brake pad is only about 50mm wide, so the WRX rotor that suits that may not suit the 2 pot pad shape???

I also measured the gap in the 4 pot calliper where the brake pads sit. On my callipers it is 28mm
The brake pad backing plates are about 5 mm thick, and seem to need 2 mm or so engagement in the calliper.
The DBA rear rotor is 20mm thick, but its minimum thickness is 18mm.
This means that if my brake pads wear out I could have them come out of the calliper.
The critical remaining pad thickness is 1mm (new rotor) or 2mm (worn rotor) which doesn't worry me too much given I'm not endurance racing
43039

[metalmaker12]

We are happy with our 2 pot and 1 pot calipers with EBC Yellow Stuff pads for autocross duty, both in terms of pedal effort and stopping ability. The car stops on a dime and we have to be conscious of not using the brakes too hard, as we can easily lock up the brakes. We adjusted the bias rearward and have the car braking fairly balanced now.

Keep in mind it takes quite a bit of effort to properly bed in brake pads. They don't work well initially (I had to stand on the brakes and I still couldn't lock them up at first), especially since the brakes are manual. We bedded in our EBC Yellow Stuff pads in at an autocross school where we got a combined 60 minutes of race time. It took over half of the school before they really started working. Now they work great and I have to be conscious of how much pedal I use, else they will lock up.

To be honest, I can't see why anyone would need "more" brake on the 818. OEM calipers with upgraded pads (if you are going to be performance driving) is more than enough in our experience. If you want lighter weight, by all means upgrade - we might in the future.

For those who have upgraded, why do you think you needed bigger brakes? Did you give the OEM pads a try at all (and if you did, did you get them actually bedded in?)? I could see perhaps for real race use, needing more cooling and/or surface area.


Agreed 100 percent

[DodgyTim]

We are happy with our 2 pot and 1 pot calipers with EBC Yellow Stuff pads for autocross duty, both in terms of pedal effort and stopping ability. The car stops on a dime and we have to be conscious of not using the brakes too hard, as we can easily lock up the brakes. We adjusted the bias rearward and have the car braking fairly balanced now.

Keep in mind it takes quite a bit of effort to properly bed in brake pads. They don't work well initially (I had to stand on the brakes and I still couldn't lock them up at first), especially since the brakes are manual. We bedded in our EBC Yellow Stuff pads in at an autocross school where we got a combined 60 minutes of race time. It took over half of the school before they really started working. Now they work great and I have to be conscious of how much pedal I use, else they will lock up.

To be honest, I can't see why anyone would need "more" brake on the 818. OEM calipers with upgraded pads (if you are going to be performance driving) is more than enough in our experience. If you want lighter weight, by all means upgrade - we might in the future.

For those who have upgraded, why do you think you needed bigger brakes? Did you give the OEM pads a try at all (and if you did, did you get them actually bedded in?)? I could see perhaps for real race use, needing more cooling and/or surface area.

Thanks Tamra, I appreciate the info. Do you use the proportioning valve in your build? to the fronts? Which brakes lock first?
Cheers
Tim

[Tamra]

Thanks Tamra, I appreciate the info. Do you use the proportioning valve in your build? to the fronts? Which brakes lock first?
Cheers
Tim

We did use the FFR proportioning valve. Without changing it, the fronts lock first and very easily. We dialed it rearward quite a bit until the fronts just lock slightly before the rears, but they are fairly balanced.

[brian b 36]

if you are looking for big but stock brakes I went with 06-09 legacy gt frt and rear brakes ,the rears are vented and works real well I have not raced it but on the street it stops great

[Bob_n_Cincy]

We are happy with our 2 pot and 1 pot calipers with EBC Yellow Stuff pads for autocross duty, both in terms of pedal effort and stopping ability. The car stops on a dime and we have to be conscious of not using the brakes too hard, as we can easily lock up the brakes. We adjusted the bias rearward and have the car braking fairly balanced now.

Keep in mind it takes quite a bit of effort to properly bed in brake pads. They don't work well initially (I had to stand on the brakes and I still couldn't lock them up at first), especially since the brakes are manual. We bedded in our EBC Yellow Stuff pads in at an autocross school where we got a combined 60 minutes of race time. It took over half of the school before they really started working. Now they work great and I have to be conscious of how much pedal I use, else they will lock up.

To be honest, I can't see why anyone would need "more" brake on the 818. OEM calipers with upgraded pads (if you are going to be performance driving) is more than enough in our experience. If you want lighter weight, by all means upgrade - we might in the future.

For those who have upgraded, why do you think you needed bigger brakes? Did you give the OEM pads a try at all (and if you did, did you get them actually bedded in?)? I could see perhaps for real race use, needing more cooling and/or surface area.

Hi Tamra,
I agree with what you did by increasing braking capability by going to a better pads.

I like the performance of my brakes using
https://www.rockauto.com/catalog/moreinfo.php?pk=2022418

Your method was a lot simpler.
Bob

[Junty]

Please could I have some feedback from other 818 builders like myself that are either go-karting or driving their cars? Aside from the active and interesting discussion regarding front versus rear callipers, without the brake booster (and following FFR build manual - moving the pivot position for brake) what is the pedal feel like? And how much pedal travel do you have with light verse heavy braking?
My pedal is very firm, only get a small movement before pressure builds. So the pedal feels very hard, and as such I have very little adjustment beneath foot between hard and soft braking.
What I'm proposing to do this week is change the stock WRX master cylinder from 1 1/16 diameter to 15/16. This should decrease fluid movement by about 20% - thus increasing both pedal movement and improving the feel of the brakes. Note: I have a huge amount of allowable travel before the pedal is near to firewall - so potentially I would almost change to 7/8 cylinder.
This is trust and hope will also decrease the force required when applying the brake - especially without the booster?
Feedback and thoughts welcome....

[Tamra]

Please could I have some feedback from other 818 builders like myself that are either go-karting or driving their cars? Aside from the active and interesting discussion regarding front versus rear callipers, without the brake booster (and following FFR build manual - moving the pivot position for brake) what is the pedal feel like? And how much pedal travel do you have with light verse heavy braking?
My pedal is very firm, only get a small movement before pressure builds. So the pedal feels very hard, and as such I have very little adjustment beneath foot between hard and soft braking.
What I'm proposing to do this week is change the stock WRX master cylinder from 1 1/16 diameter to 15/16. This should decrease fluid movement by about 20% - thus increasing both pedal movement and improving the feel of the brakes. Note: I have a huge amount of allowable travel before the pedal is near to firewall - so potentially I would almost change to 7/8 cylinder.
This is trust and hope will also decrease the force required when applying the brake - especially without the booster?
Feedback and thoughts welcome....

Have you bed in the brakes yet? Ours required more effort (to stop quickly) than I weighed enough to produce before they were bedded in. Now they are great and very easy. We do have upgraded pads.

Also, we prefer force modulated rather than travel (mushy) modulated brakes. That doesn't mean high effort though.

[CNC_Geek]

Just curious. Has anyone actually fit a stock Subaru brake booster onto the area provided? I tried and there was no physical space for this. Received my kit last April. Not sure if the chassis was redesigned from earlier 818 kits.

[Bob_n_Cincy]

Just curious. Has anyone actually fit a stock Subaru brake booster onto the area provided? I tried and there was no physical space for this. Received my kit last April. Not sure if the chassis was redesigned from earlier 818 kits.
CNC
I don't know if this will help. These is the only pictures I have of the brake booster.
Bob

43110 43111 43112 43113 43114

[Junty]

Thanks Tamra, Absolutely brakes are well bedded in. As with everything in my build I have new parts all around and included a higher spec set of pads (still stop when cold - with good heat range for track). I haven't yet tried drilled or slotted rotors.
Also - I'm certainly not knocking the 818s stopping ability, it stops well. What I'm however looking for is incredible stopping ability. My 818s has a near new 2012 2.5L WRX engine with VF52 turbo - due to late model engine I've added Motec M800 ECU. It has a very conservative tune - on the dyno at 12PSI produces 247KW. It was also pushed a little harder to 16PSI and here was 287KW, but I want to learn more about the cars balance and drive before running the higher spec tune... We are lucky in Australasia that we have JDM spec Subarus. I'm sure you can imagine - this is a very rapid vehicle 0-100mph is phenomenally quick - I merely want the 100mph back to naught to be equally mind stopping! Note for USA HP folk - convert kw to HP by multiplying by 1.34, so 247kw = about 330HP (287 = 385).

[xxguitarist]

Junty,
With our 2 pot fronts, 1 pot rear, EBC Yellowstuff pads, we are able to lock up 245 Hoosier A7s.
Unless you have HOT true race tires, or more tire width than fits under the car (more grip than DOT-R comps), there's no stopping any faster than we do.

What's your problem with the existing brakes? Tire grip, brake bite & power, or eventual brake fade after repeated lapping?

We would challenge that the first 2 aren't actually a problem. We aren't driving road course, so the third could catch up with you theoretically.

On feel, it is much harder to modulate brakes that have variable pedal travel. I love brakes that have a tiny bit of take-up, then the pedal is dead solid, with just force modulation. Additional travel is asking for difficulty quickly modulating, and even more problems with heel-toe downshifts, since the brake pedal has different heights based on how hard you're braking. We don't have a low power car, either.

[Junty]

Hey Andrew and Tamra, thank you for feedback and support. My 818 stops well, and certainly if I stomp the brakes to haul up quickly - it will certainly lockup and R888's will slide (with ABS off). However I still want better braking - better pedal feel, and if I modulate the pedal I want it to stop so that it feels like I'm stripping the tarmac off the road - not just shreading/skidding tyres.
So completed today - I have fitted 2 rebuilt 2 pot Legacy GT front callipers with new 294mm rotors. Ive also now finished installing my 2008 (4 pot WRX) front rotors to the rear along with DBA4657S rear rotors. These are slotted (couldn't get standard) with 170mm handbrake and 316mm diameter. Ive also fitted new HAWK Street/Race pads to front and rear. Finally I also fitted a new 15/16 master cylinder.
Although still running all the setup in, it immediately feels great. Pedal moves a little easier - not as a boosted WRX - but has good gradual uptake for nice street driving - then with a little push brakes bite hard and pull evenly.
Previously on other brake discussions/forums I've liked the concept of matching front and rear brake size and force. Similar to many other mid-engine or rear engine sports cars which have identical front and rear brakes. I now have (from Bob's calculations above) 3.37" brake calliper (force/area) front and 3.082" rear - with no brake bias.

[matteo92065]

I've been driving mine for 2 weeks now. I have STI Brembos w/yellow stuff on drilled/slotted rotors in front and Red stock WRX brakes in the back. ABS is on a switch. There are two proportioning valves on the front wheels.
I can't get my rears to lock up. I know my system is very unbalanced. Due to vanity issues, I can't give up the Brembos and go to an Impreza caliper :rolleyes: I am going to try the rear Wilwood 4 piston brake kit, #140-13013-DR. Gut feeling tells me it will be more balanced then, and look great.
I should do the force/area calcs described above.

[Bob_n_Cincy]

I've been driving mine for 2 weeks now. I have STI Brembos w/yellow stuff on drilled/slotted rotors in front and Red stock WRX brakes in the back. ABS is on a switch. There are two proportioning valves on the front wheels.
I can't get my rears to lock up. I know my system is very unbalanced. Due to vanity issues, I can't give up the Brembos and go to an Impreza caliper :rolleyes: I am going to try the rear Wilwood 4 piston brake kit, #140-13013-DR. Gut feeling tells me it will be more balanced then, and look great.
I should do the force/area calcs described above.

Matt,
Before you spend the money on the #140-13013-DR look at the piston diameter.
They are design for stock Subaru and have only about half the braking force as the fronts.
Bob

[matteo92065]

Matt,
Before you spend the money on the #140-13013-DR look at the piston diameter.
They are design for stock Subaru and have only about half the braking force as the fronts.
Bob

You're right. All the specs are about the same as stock WRX. Just the pad size gets bigger. Thanks.

[xxguitarist]

I've been driving mine for 2 weeks now. I have STI Brembos w/yellow stuff on drilled/slotted rotors in front and Red stock WRX brakes in the back. ABS is on a switch. There are two proportioning valves on the front wheels.
I can't get my rears to lock up. I know my system is very unbalanced. Due to vanity issues, I can't give up the Brembos and go to an Impreza caliper :rolleyes: I am going to try the rear Wilwood 4 piston brake kit, #140-13013-DR. Gut feeling tells me it will be more balanced then, and look great.
I should do the force/area calcs described above.

You say red WRX brakes in the back. Do they also have Yellowstuff pads, or do they have Redstuff pads? You could go down on the front pad if you felt it was necessary to shift the bias rearward more than you can accomplish with the prop. valve.

[matteo92065]

You say red WRX brakes in the back. Do they also have Yellowstuff pads, or do they have Redstuff pads? You could go down on the front pad if you felt it was necessary to shift the bias rearward more than you can accomplish with the prop. valve.

Yes, stock pads on the rear red colored calipers. I can see the confusion. There are so many combinations!

So, maybe a harder compound in the front, and softer in the rear? Any recommendations?

Wilwood does have three different calipers that would bolt right onto their system. Only difference being the piston areas, 1.58sqin, 2.46sqin, and 4.8sqin. The 2.46sqin looks closer to the 3.38sqin of the front than the current 1.50sqin.

[xxguitarist]

Yes, stock pads on the rear red colored calipers. I can see the confusion. There are so many combinations!

So, maybe a harder compound in the front, and softer in the rear? Any recommendations?

Wilwood does have three different calipers that would bolt right onto their system. Only difference being the piston areas, 1.58sqin, 2.46sqin, and 4.8sqin. The 2.46sqin looks closer to the 3.38sqin of the front than the current 1.50sqin.

Wow, with Yellowstuff up front, and stock in the back, I'm not surprised you want more rear bias! That's even ignoring the larger calipers up front..

We have yellowstuff all around, with 2 pot fronts, 1 pot rears. We were able to get balanced braking from a few turns of the adjuster knob. Lots of stopping force, with firm but reasonable pedal effort.

Miata autox setup (no brake bias valve) says to correct the front bias, use one step down pad in front vs rear- red/green stuff front, yellowstuff rear, etc. The same can be done to correct bias on the 818 if your setup is beyond what you want to do with a Prop valve.

[flynntuna]

Forgive the newb question. Are you saying you can adjust the bias front/rear by using different pads for the front and rear, fo instance stock front, yellow rear?

[Tamra]

Yellow Stuff pads are stronger than stock pads, so if you only put them on one end of the car, it would make that end have more braking bias.

The FFR bias adjuster also can adjust the bias rearward, but since he put SO much brake on the front of the car and so little on the rear, it probably doesn't have enough adjustment to even it out.

[flynntuna]

So, are you saying that switching to "better" pads in the rear, would be equivilant to upgrading to larger disc and caliper in the rear?

[xxguitarist]

Yes, a pad with more bite will increase braking force on that end of the car. It's vaguely equivalent as far as stopping ability goes.

The other advantage of larger brake components is heat. Higher end pads also handle heat better, but not to the same degree as larger brakes.

[flynntuna]

More food for thought, thanks.

[Junty]

Hey Matteo92065. Rather than decreasing the front - why not try similar to my addition (originally Bob's idea) and put standard WRX 4 pot callipers on the rear? I would also add the same yellow stuff pads - just to keep things similar all around? The DBA rotors ensure that you keep the hub plate and handbrake assembly unchanged. As shown by Bob above - there is a minor hole relocation required to bolt the 4 pots on - but this is an easy mod...

[matteo92065]

Junty, I will look into increasing the rear rotor/caliper size. I will never go smaller!!! I've got so many other little things to take care of, I'll get new pads front and rear for now.

[C.Plavan]

My .02 cents (Again). I keep seeing these brake/caliper threads....... you really do not need to change anything with the brakes.
1. 4 pot Wilwoods front and rear (kit). (12" rotors)
2. Wilwoods are extremely light over the stock stuff.
3. Save your money and do not get the bigger brakes.
4. Do not overthink the brakes, the car is light, and my 818R is heavier than any street 818S (minimum race class weight with me in it (HP/WT) 2266 pounds).

I mated these up with Raybestos ST46 pads(or ST43 cant remember right now). Braking is really, really good (130 mph+ to 40mph many times). I adjusted them with my dash mounted bias control.

[Bob_n_Cincy]

My .02 cents (Again). I keep seeing these brake/caliper threads....... you really do not need to change anything with the brakes.
1. 4 pot Wilwoods front and rear (kit). (12" rotors)
2. Wilwoods are extremely light over the stock stuff.
3. Save your money and do not get the bigger brakes.
4. Do not overthink the brakes, the car is light, and my 818R is heavier than any street 818S (minimum race class weight with me in it (HP/WT) 2266 pounds).

I mated these up with Raybestos ST46 pads(or ST43 cant remember right now). Braking is really, really good (130 mph+ to 40mph many times). I adjusted them with my dash mounted bias control.

Hi Chad
Your advise is worth much more than 2 cents.
I totally agree with you.
I believe you have a balance bar pedal system which allows you to take pedal force from the front and move it to the rear.
The proportional valve only reduces the front and doesn't add anything to the rear.
Is it easy for you to take a picture of your balance bar position to see (count threads) how far it is shifted on way?
Bob

Edit: Chad, I just looked back and see you are using a proportional valve with better pads.

[metalmaker12]

My .02 cents (Again). I keep seeing these brake/caliper threads....... you really do not need to change anything with the brakes.
1. 4 pot Wilwoods front and rear (kit). (12" rotors)
2. Wilwoods are extremely light over the stock stuff.
3. Save your money and do not get the bigger brakes.
4. Do not overthink the brakes, the car is light, and my 818R is heavier than any street 818S (minimum race class weight with me in it (HP/WT) 2266 pounds).

I mated these up with Raybestos ST46 pads(or ST43 cant remember right now). Braking is really, really good (130 mph+ to 40mph many times). I adjusted them with my dash mounted bias control.

Ditto

[DodgyTim]

Just to close off this upgrade, I chose to go ahead for the following reasons:

1 I have to pass a brake test prior to registration. They formally measure deceleration under heaps of conditions include cold stop, fade resistance (15 consecutive 100 kmh stops), and there is a limit on the allowable brake pedal force that can be applied (500 newtons or about 50kg force).

2 They limit the use of proportioning valves to “Proportioning valves can only be used to correct a small imbalance”. One of the tests is performed with the proportioning valve disconnected.

In addition to the 2006 4 pots and the 316mm diameter rear rotors, I’ve opted to swap the master cylinder to the 7/8” diameter unit (The OE Nissan part number is 46010-1M320, thanks to lap_dog) to try and reduce pedal effort.

The backing plates I used were from a Forester that had standard brakes, they were the closest standard fit. The 4 pot front callipers have much longer mounting arms than the 2 pot rears they replace.
45051


I machined the calipers a little bit (actually a bit more than is shown in the right hand side of the photo), relocated the holes in the backing plate, and welded in some reinforcement to the backing plate where the old holes were.
450504505245053

Final fitment was good and the service brake (park brake) works as standard.
4505445055

Before
45056

After
45057

[Bob_n_Cincy]

Just to close off this upgrade, I chose to go ahead for the following reasons:

1 I have to pass a brake test prior to registration. They formally measure deceleration under heaps of conditions include cold stop, fade resistance (15 consecutive 100 kmh stops), and there is a limit on the allowable brake pedal force that can be applied (500 newtons or about 50kg force).

2 They limit the use of proportioning valves to “Proportioning valves can only be used to correct a small imbalance”. One of the tests is performed with the proportioning valve disconnected.

In addition to the 2006 4 pots and the 316mm diameter rear rotors, I’ve opted to swap the master cylinder to the 7/8” diameter unit (The OE Nissan part number is 46010-1M320, thanks to lap_dog) to try and reduce pedal effort.

The backing plates I used were from a Forester that had standard brakes, they were the closest standard fit. The 4 pot front callipers have much longer mounting arms than the 2 pot rears they replace.
45051


I machined the calipers a little bit (actually a bit more than is shown in the right hand side of the photo), relocated the holes in the backing plate, and welded in some reinforcement to the backing plate where the old holes were.
450504505245053

Final fitment was good and the service brake (park brake) works as standard.
4505445055

Before
45056

After
45057

Great Job Tim
With equal calipers F&R and running 235F and 255R tires, I am very close with no PV. So close I cannot decide where I should put it in. I am leaning toward putting it in the rear.
Are you going to go aggressive on the pads?
Bob

[DodgyTim]

Great Job Tim
Are you going to go aggressive on the pads?
Bob

Not initially Bob, for the pre registration test I need good performance from first stop, I'll look at better ( I have currently got high performance street pads in) if I need more brake when racing

[Tamra]

That sounds like an intense braking test. I hope the rest of the inspection isn't so rigorous! I expect you'll pass this portion with flying colors as long as you get the pads bedded in properly beforehand. Which performance street pads did you go with?

[Innkeepr]

Ok guys,

this build is going to take me a while. My MKII build was 8 years- that's the price of being a single income public servant and raising a family.
Now, with the eldest starting college, and the second not far behind, it will likely be a long term build again ( hope not as long )

I am piecing this together, gathering as I go based on the FFR manual build list.
I purchased a JDM EJ207 complete minus intercooler, has all wires & computer - but will build another mega squirt for mgt.

As I comb the yards around here, what will work best ? mixing/matching and not knowing what will/will not work is going to be wasted cash.
I have read that you should match the MC to the calipers/ ie, use all parts from an 06 ( MC / booster/ calipers )

Seeing how Bob, Plavan, Mechie, & Metal are on top of these cars, it would be great if you guys could start a thread about which parts
you could scavenge, what works best - for those who of us who are putting Frankenstein together without a donor.

So far, I was told to get the 06 steering rack ( better ratio ? ) and get 06 wrx brake system ?

Any thoughts ?

thanks & be safe.
"E"

[DodgyTim]

That sounds like an intense braking test. I hope the rest of the inspection isn't so rigorous!
Much worse actually, I'll post on the chassis torsion and beaming test soon:)

[Harfang2]

Just to close off this upgrade, I chose to go ahead for the following reasons:

1 I have to pass a brake test prior to registration. They formally measure deceleration under heaps of conditions include cold stop, fade resistance (15 consecutive 100 kmh stops), and there is a limit on the allowable brake pedal force that can be applied (500 newtons or about 50kg force).

2 They limit the use of proportioning valves to “Proportioning valves can only be used to correct a small imbalance”. One of the tests is performed with the proportioning valve disconnected.

In addition to the 2006 4 pots and the 316mm diameter rear rotors, I’ve opted to swap the master cylinder to the 7/8” diameter unit (The OE Nissan part number is 46010-1M320, thanks to lap_dog) to try and reduce pedal effort.

The backing plates I used were from a Forester that had standard brakes, they were the closest standard fit. The 4 pot front callipers have much longer mounting arms than the 2 pot rears they replace.
45051


I machined the calipers a little bit (actually a bit more than is shown in the right hand side of the photo), relocated the holes in the backing plate, and welded in some reinforcement to the backing plate where the old holes were.
450504505245053

Final fitment was good and the service brake (park brake) works as standard.
4505445055

Before
45056

After
45057

Hi guys, i have built an 818 S in 2014 and now thats road legal in QC Canada since 2016. I did a lot of lapping on small and big track and this winter i search some upgrade on the forum. I have buy a set of wildwood rally Subaru front brakes kit with 6 pistons and the braking is really better now but the
rear Wrx stock brake is too small and need more cooling (they becoming RED after 10mins).So i found this tread and i found the DBA rotor set but before going further, i want to know if you have good result or upgraded something since 2015 and if the 4 pots on the back braking more/equal than the wildwood 4 pistons set. This is not a race car but you know on the track this car kick a Audi R8 v10 *** hahaha and my brake is my limit for now.
Thanks for the picture and information. I will probably go with a 7/8 master cylinder too if the feeling of the brake pedal is more easy/sensitive than the 5/8 .

[DodgyTim]

I'm happy with the setup, I still run it as seen in the photos above, with virtually no bias adjustment.
I haven't tested any other setup to compare with, there was a local 818 with the wilwood setup, but unfortunately I didn't get a drive:(
These brakes are quite heavy, if I was doing it again I'd look seriously at the Cadillac CTS kit too. Those kits got popular after I completed my mods

[Harfang2]

Thanks for the inside! I will take a look to the cadillac caliper too... I have already find a potential seller for the 4 pots subaru and i have found the disc like the dba on KNS brake website for less and thats the same buisness that making disc for DBA. And for the 7/8 master cylinder have you found a big difference on the pedal brakes because i have buy the kit without the wildwood dual cylinder option .
Thanks

[DodgyTim]

Sorry, I didn't try the standard 1" master, I've only used the 7/8", so I can't tell you how much difference it made
Pad selection is important to pedal effort too. I'm still running performance "street" pads, the pedal effort is OK
Cheers

[prematureapex]

Instead of those expensive conversion rotors, I think I'll buy a set of those modified/thicker parking brake shoes and run stock STI rear rotors. Generics are like $30 a piece.

[prematureapex]

Just to close off this upgrade, I chose to go ahead for the following reasons:

1 I have to pass a brake test prior to registration. They formally measure deceleration under heaps of conditions include cold stop, fade resistance (15 consecutive 100 kmh stops), and there is a limit on the allowable brake pedal force that can be applied (500 newtons or about 50kg force).

2 They limit the use of proportioning valves to “Proportioning valves can only be used to correct a small imbalance”. One of the tests is performed with the proportioning valve disconnected.

In addition to the 2006 4 pots and the 316mm diameter rear rotors, I’ve opted to swap the master cylinder to the 7/8” diameter unit (The OE Nissan part number is 46010-1M320, thanks to lap_dog) to try and reduce pedal effort.

The backing plates I used were from a Forester that had standard brakes, they were the closest standard fit. The 4 pot front callipers have much longer mounting arms than the 2 pot rears they replace.
45051


I machined the calipers a little bit (actually a bit more than is shown in the right hand side of the photo), relocated the holes in the backing plate, and welded in some reinforcement to the backing plate where the old holes were.
450504505245053

Final fitment was good and the service brake (park brake) works as standard.
4505445055

Before
45056

After
45057

Thinking out loud...

Do you think I could run a spacer on the hub to center the rotor vs. machining the caliper ears?

And along those same lines, you don't happen to recall how much you took off do you? Or the resulting thickness of the ear?

[DodgyTim]

The main point of machining the ears, and relocating the holes in the backing plate, was to move the caliper in closer to the axle centerline.
Otherwise the pad would overhang the outer edge of the disk.
I can measure the final thickness this weekend if you like

[prematureapex]

I knew part of it was to accomplish that, I just thought you thinned it down to center the rotor as well. Based on my initial measurement, looks like 2.5-3mm puts the rotor in the middle of the caliper on the stock ear thickness. Then again, with a 20mm rotor, maybe there is enough extra room that you don't have to center it really at all.

Sticking point being, I can crudely clear material away radially with a grinder, etc. but without a mill, I couldn't do the depth cuts. While I can get to a mill, I think a grinder and a 3mm spacer could get the job done.

[prematureapex]

Tim/Bob,

Any tips for locating the holes accurately? I'm finding it tough to clamp the caliper in place with the rotor on (and still be removable) to ensure pad alignment. Maybe mark the back of the caliper with the rotor on, remove the rotor, and then clamp/mark hole/drill according to the marking? But that doesn't seem too accurate.

I'm probably missing an easier way to do it...

With a junk backing plate, I tried Bob's way of opening up one of the holes, and relocating only the other. But with the 4-pot pad shape, that doesn't seem to work without a bit of pad overhang (which isn't the biggest deal, but not ideal).

Thanks!

[DodgyTim]

It's been ages since I did the mod, but from memory I temporarily bolted the backing plate and rotor to the spindle, trial fitted the caliper (with worn/without pads) and aligned the pad retaining pins to the outside of the rotor, checking the inner clearance on the rotor hub too.
I then center punched the backing plate and drilled 2 slightly oversized holes.
I re-assembled everything with the weld-on washers + bolts etc and positioned it exactly as I wanted it, snugged up the bolts and tacked the washers in place.

The calipers bolts were a close fit to the washer holes, not the holes in the backing plate
Cheers

[prematureapex]

OK, finally finished welding this up. Thanks Tim for the above, my issue was the step between putting the rotor on, and center punching the holes. As you have to take the rotor off do do that, but taking the rotor off meant moving the caliper and losing the hole location.

When it was said and done, my holes were more like rough slots from the factory holes to their final resting place ( I was using hand tools in an inappropriate manner). In view of that, I used 3/16" stock and an angle grinder to make thick patches vs. using thinner washers as you did. Overall, I think it will be AOK.

At full thickness, however, the inner pad just barely doesn't fit...so I'm thinking I'll need to space the rotor out via a wheel spacer at least until the pad wears a bit (then I can move to a shim on the outer pad).

At $40/piece for STI rotors, $190 for e-brake shoes, and $112/per for reman calipers. This is certainly the cheap way to give yourself PLENTY of rear brake with cheap consumables. Same pads F/R is also a nice plus. The more I think about it, even many of the expensive aftermarket solutions are designed for the Subaru, which means they still don't provide enough clamping force.

I'll post pictures of my awful work later...:(

103755103756103757103758

[tmoretta]

I am looking, with much interest, at this thread about using the 4 pot calipers in the rear of the 818. I already am using the H6 rear rotors on my car and am still unhappy with the braking. I have '02 WRX front calipers on the car now. A few questions/concerns: What model/year of subie 4 pot calipers should I use on the rear? Can I continue to use the H6 rotors, or is it best to source some others? Will worn brake pads pop right out of the wider 4 pots when used on the narrower (non vented) rotors? How much modifying needs to be done to the backing plates and/or rotor hubs?

[Bob_n_Cincy]

I am looking, with much interest, at this thread about using the 4 pot calipers in the rear of the 818. I already am using the H6 rear rotors on my car and am still unhappy with the braking. I have '02 WRX front calipers on the car now. A few questions/concerns: What model/year of subie 4 pot calipers should I use on the rear? Can I continue to use the H6 rotors, or is it best to source some others? Will worn brake pads pop right out of the wider 4 pots when used on the narrower (non vented) rotors? How much modifying needs to be done to the backing plates and/or rotor hubs?

Tmoretta,
At one point I was running H6 rotors, with 04FXT front calipers. I took an old pad backing plate and welded it to the new outside pad. this prevented the pad from falling out if worn out. Changing to the DBA rotor eliminated this issue.
Bob

104463

[tmoretta]

What is the DBA rotor? Same diameter? Uses E brake?

[Bob_n_Cincy]

What is the DBA rotor? Same diameter? Uses E brake?

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

DBA2657 are 5 x100mm lugs, 170mm e-brake, 20mm thick.
see attached. Available from summit.


104474

[DodgyTim]

The original 4 pot calipers I used suited a 295 dia x 25 thick rotor. They were sourced from 2006 or 2007 WRX's, though they do come on some other Subaru models too.
The DBA 42657 is 316mm diameter and 20 mm, thick so if my pads got down to less than 2.5mm thick, they'd be further out than standard fitment

The good features of the DBA rotor is that it keeps the standard 170mm dia handbrake and 5x100 stud pattern.
Overall this was a good mod for me because the
calipers were free
pads are the same front/rear
The downside is they are quite heavy. When I did this there wasn't much chatter about the Cadillac CTS caliper swap, if I was doing it now I'd look at that too

[prematureapex]

As I mentioned before, the other option is to use a stock 2004 STI rear rotor (190mm ebrake drum), and buy/have made thicker shoes to maintain the ebrake. Godspeed brakes makes them out of the UK.

https://www.godspeedbrakes.co.uk/276-rear-brembo-adapter-kits-

If you're going to track the car, you're going to go through rear rotors. So for me it made sense to spend the $200 on the shoes up front, so I can buy $80/pr. generic STI rotors vs. the unique $300/pr. DBA conversion rotors.

Although either option is good.

As far as machining goes, you can get it done with an electric angle grinder and a drill if you're handy...but you'll want to have some washers or patches welded on when you're done. Took a few hours in the basement.

+1 on the caliper weight, that's the drawback. But if the car needs more brakes, and you don't want to drop a ton of money...this is a good solution imho.

[walt555]

I am looking, with much interest, at this thread about using the 4 pot calipers in the rear of the 818. I already am using the H6 rear rotors on my car and am still unhappy with the braking. I have '02 WRX front calipers on the car now. A few questions/concerns: What model/year of subie 4 pot calipers should I use on the rear? Can I continue to use the H6 rotors, or is it best to source some others? Will worn brake pads pop right out of the wider 4 pots when used on the narrower (non vented) rotors? How much modifying needs to be done to the backing plates and/or rotor hubs?
If your still having high pedal force to stop, I think it has more to do with pedal ratio than more or bigger brakes. For stock wrx pedals "Hindsight" drilled holes 7/8ths inch up and 1 1/4th inch up. The 7/8th was better than the ffr 1/2 inch and the 1 1/4" was spongy. So I'm thinking 1 inch up from stock. Better yet talk to wilwood about a pedal box for you application. Hope this helps!

[Bicyclops]

Howdy,

I read all this stuff three years ago and made some of my decisions based on advice gleaned. I went with Cadillac Brembos on all four with 04 STI front rotors. I'm using, so far, generic Delco ATS brake pads. Might go to better pads as I get it dialed in better. I added Wilwood cable actuated E-brakes to get legal. I drilled the FFR hole higher up the pedal and following Hindsight's advice, another hole higher than that. Like most I found the brake pedal very hard and couldn't lock them or even really panic stop even with every thing I could do on the pedal. Been so busy having 500 miles of canyon road fun, where I didn't really use the brakes much, I ignored the lack of braking ability. Today I tested with the clevis pin in the top hole and it made a world of difference. I was able to lock the rears @ 40mph. I put my bias valve in the rear circuit. I've turned the bias out 1 full turn and have yet to test that.

Got back from test drive. Brakes are awesome. Very happy with them.

Ed

[blomb11]

Howdy,

I added Wilwood cable actuated E-brakes to get legal.

Ed

How did you get an e-brake with the Cadillac brembos and STI rotors? I don’t think my line lock will pass the CA inspection.

[prematureapex]

How did you get an e-brake with the Cadillac brembos and STI rotors? I don’t think my line lock will pass the CA inspection.

You can order thicker ebrake shoes from the UK. I believe I posted the link earlier in this thread.

[blomb11]

You can order thicker ebrake shoes from the UK. I believe I posted the link earlier in this thread.

Ah yes I see it now...I should have read the whole thread. My google skills are not working well to try and figure out the pad wear surface dimensions of the DBA 2657S conversion rotor (170mm ebrake). I have 5x100 STI front rotors on the rear now so I will measure the wear area, see if I can try to compare it online, or maybe just buy a DBA rotor to measure. It seems like as you and others have done adding material to offset the Cadillac caliper could work. My question/concern is the front and rear pads are usually different sizes with the rears being smaller. I can't remember if this is a pad height or length difference. If the pad height is the same front to back then I think it will work just need to modify the OEM caliper bracket. Sucks that when I moved I tossed all of the rear brackets and ebrake stuff.

[Bob_n_Cincy]

to try and figure out the pad wear surface dimensions of the DBA 2657S conversion rotor (170mm ebrake).

186928

[Bicyclops]

I used '04 STI rotors front and rear and the Caddy Brembos. With no hat section, you can't do drum E-brakes so I went to the Wilwood units. I think they might be kart brakes. I don't have the model number handy, but I did find them by searching the Wilwood site. The cables are also Wilwood. I used an aftermarket brake handle, Lokar I think. I'm very happy with this setup.

Ed

186941