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  #1  
Old 03-24-2010, 11:50 PM
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sperry sperry is offline
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STi brakes, the brute force way!

So, I was fed up with the brakes on my SVX... not just with the poor pedal feel, but also with the lack of heat capacity (I'm an SCCA driving instructor, so every now and then the SVX sees the race track, and I get one or two good stops out of the car before the pads are faded). Sure, the brakes are adequate for driving around on the street... but I've seen the light with my StopTechs on my WRX, and I want that on the SVX too.

Additionally, and probably a big contributor to the poor brake feel on my SVX, my wheel bearings are on their way out. I've to the point where I'm getting quite a bit of brake drag as well as pad knock-back due to the bearing flex, so I decided to kill two birds with one stone. The stone in this case is a pair of StopTech 328x28 brakes for a WRX mounted on a set of '07 STi knuckles and hubs adapted to the SVX.

The STi knuckles are pretty close in shape to the SVX, but they're not straight bolt in. So far, I haven't sorted out all the issues quite yet, but I have made a bunch of progress. Here are all the issues as I see them, and my solution so far:

1) Suspension upright mounting - the spacing between the holes on the SVX uprights is just a little tighter than on the STi. One solution would be converting to STi suspension, but that just pushes the problem out to the top-hats and there's of course the whole strut length deal. I'm choosing just to slot the lower hole on the knuckle enough to allow the stock suspension to bolt up. This also leaves me the option of switching to STi struts in the future.

2) Ball-Joints - the SVX uses an inverted (when compared to the STi) ball-joint that is attached to the LCA with three bolts. This is a pretty different design than the STi... but it actually works in our favor. After taking a bunch of measurements, it is actually pretty simple to build a ball-joint adapter that will bolt to the SVX's LCA and hold an STi ball-joint. The best part is that because of the difference in ball-joint angles between the two knuckles, the STi adapter is actually *simpler* than the existing SVX ball-joint part. Here's my design for the part... I haven't gotten around to fabricating it yet... I'm torn between trying to do it myself, or finding a machinist to make it for me. The only hard part is drilling the proper bevel for the ball-joint... it's a weird angle and needs to be pretty accurate to ensure the ball-joint mounts without any slop.



The adapter is made from a simple piece of hot-rolled 3"x.5" flat bar, with the ball-joint mount section made from stacking the bar at double thickness. Certainly a lot easier than my first design that was going to cost like $200 each to be made at eMachineShop.com out of a big old solid CnC'd block of steel. Once again, it's just figuring out how to get a good angle on that ball-joint socket that's kept me from cutting this in my garage.

3) ABS sensor - the ABS sensor on the SVX is much longer than the one on the STi as it pokes horizontally through the knuckle to read the tone wheel mounted on the back of the hub. The STi's ABS sensor points at the tone wheel mounted on the axle itself. The good news is that the tooth count on both tone wheels is exactly the same... so the hall-effect sensors will see the same number of pulses per rotation of the wheel whether or not its coming from the hub or the axle. So, I've decided I'm going to put STi front axles on my car to match the knuckles/hubs. The good news again is that converting the SVX transmission to accept the STi axles is just a matter of two new oil seals. Just pop out the stub-axles, swap the oil seals for the slightly larger STi seals, and pop in the STi axles. Or at least it's that simple in my head... we'll see once I get the seals I ordered and actually try it. The big down side of this is the cost of STi axles... list price is north of $400 *each*. At that price, I'll bet many folks would rather just go without ABS. Like I said, this is definitely the "brute force" means to big brakes. Finally, in order to get the SVX ABS sensors to bolt into the STi knuckles, I'm going to have to fab a riser of sorts. I'm willing to be a set of STi ABS sensors would splice in, but I'm going to try to reuse the SVX's parts first on this one.

4) The brakes - after all, that's the whole point of this, right? Obviously, once you've got STi knuckles and hubs on the car, any brakes that work on the STi will work. Having raced with StopTechs for the last 5 years or so, I'm a huge fan of their brakes. IMO, you get the same quality brakes as the *race* Brembos at the same price as the street Brembos. I ended up grabbing a set of the WRX 328x28mm StopTechs from someone on NASIOC. I expect the brake bias shift to the front won't be so bad if I use the slightly smaller WRX BBK over the STi BBK. The only caveat is to make sure you get the rotors with the dual bolt pattern, or you'll be visiting the machine shop to get the rotors drilled.

5) Wheels - you're going to need some big wheels. Once again, anything that fits the STi. Unfortunately for me, I have an awesome set of 17x9 Enkie RPF1's that I absolutely *love* on the SVX. The problem is that they don't clear the big brakes. In fact that's why they're on my SVX, since I originally bought them for my race car, but ended up putting them on the SVX when I found out they wouldn't clear the StopTechs. So now I'm selling my wheels... however, another option I'm considering is to slap a 15mm spacer in there up front, which should give me the clearance I need, plus it should help handling a touch by taking away a little of the understeer. I figure, with the massive new unit bearings up front, I can probably get away with a 9" wide rim with the equivalent of a +30 offset, as long as I'm not rubbing the fenders. I certainly wouldn't recommend it on the stock bearings.

6) Suspension Geometry - I wonder what the end result will be. I did try to do my due diligence, and took a bunch of photo graphs to compare the angles between the two knuckles. The angle between the hub face and upright is the same between the two. The angle of the ball joints is the same once you switch to a flat mount as diagrammed above. But there is a slight difference in the axis point on the ball-joint because the SVX is inverted vs the STi. The steering arms are the same length and height. I'm pretty convinced the geometry will be nearly identical after the swap... but there is always the off chance of introducing some bumpsteer if the LCA angle and tierod angles are off from each other. Then again, it's probably not any worse than the scrub angle I'm going to get from running the wide tires.

So, in summary, I think this is doable... to the point where I've already bought a stack of parts. Once I get everything assembled, I'll take some pictures and post up all the additional problems I encounter, hopefully with their solutions as well.

Then of course, there's the whole rear brakes to worry about. Perhaps I'll start looking at that after/if I get a 6MT and R180 back there... some STi rear knuckles and 2-pot brakes would be nice.
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Last edited by sperry; 03-24-2010 at 11:52 PM.
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  #2  
Old 03-25-2010, 12:16 AM
Pegdrgr Pegdrgr is offline
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Re: STi brakes, the brute force way!

Excellent information!

Let me know if you are looking for STi axles, I have a new pair that were installed in a car but never used. For the cause I would be willing to make you a great deal on them.

I started to look into this myself, but I was looking to see if I could put the STi control arm in there. Sounds like you have a very doable way to get it done.

I know that you can get a ball joint taper bit, although I am not positive it is the same angle as the Subaru ball joint.

Jarrad
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  #3  
Old 03-25-2010, 12:24 AM
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sperry sperry is offline
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Re: STi brakes, the brute force way!

Quote:
Originally Posted by Pegdrgr View Post
Excellent information!

Let me know if you are looking for STi axles, I have a new pair that were installed in a car but never used. For the cause I would be willing to make you a great deal on them.

I started to look into this myself, but I was looking to see if I could put the STi control arm in there. Sounds like you have a very doable way to get it done.

I know that you can get a ball joint taper bit, although I am not positive it is the same angle as the Subaru ball joint.

Jarrad
I just ordered some axles from the dealer (haven't received them yet)... got a raging good price on them because the parts guys are nice enough to give me cost + tax on most items since I'm in there replacing the stuff I break on my track car all the time. But I'd be really interested in finding out what you want for those axles. Even the good price on the new ones put me over my budget, since I was figuring on being able to get some remanufactured axles for this swap.

Want to PM me a price? I'm afraid the shipping costs may end up eating up whatever you could save me though... axles are big and heavy!
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  #4  
Old 03-25-2010, 01:39 AM
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icingdeath88 icingdeath88 is offline
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Re: STi brakes, the brute force way!

Very cool project. I love whenever someone does enters uncharted territory. Be sure to keep us posted as you go along. If you've got some handy, I'd love to see some pics of the STi and SVX parts differences, to help me understand what exactly you're trying to do here.
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Old 03-25-2010, 01:51 AM
1986nate 1986nate is offline
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Re: STi brakes, the brute force way!

Quote:
Originally Posted by sperry View Post
Even the good price on the new ones put me over my budget, since I was figuring on being able to get some remanufactured axles for this swap.
I was going to ask about that. No one does any remans for those yet then? I would imagine in the next couple years that some company would be picking them up which would drastically reduce cost.
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Old 03-25-2010, 07:17 AM
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Re: STi brakes, the brute force way!

If you pay a shop to make these, please let me know as I will take a set as well (maybe defray the costs a bit). I have been looking at this specific problem recently and really like what you have come up with here...
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  #7  
Old 03-25-2010, 11:04 AM
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sperry sperry is offline
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Re: STi brakes, the brute force way!

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Originally Posted by 1986nate View Post
I was going to ask about that. No one does any remans for those yet then? I would imagine in the next couple years that some company would be picking them up which would drastically reduce cost.
Unfortunately, the STi axles just haven't been around long enough for them to have failed and ended up as cores in the remanufacturing system in any quantity... so no one seems to offer remans. I would expect reman'd STi axles to run around $100-$150 each... which would be a hell of a lot more affordable than buying new at $420 each.

At this point the cost of the axles in this swap is by far the most expensive part, aside from the StopTech brakes themselves... but I expected the brakes to be expensive. Knuckles are about $200 each, hubs about $200 each. I'm not sure what the ball-joints cost because I already had a pair lying around. The ball-joint adapter will cost probably around $100 a pair.

So, without the axle swap, this is around a $1000 job + the cost of the brakes you choose. Perhaps less if you're lucky to find a set of used STi brembos on the spindles/hubs.
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Old 03-25-2010, 12:05 PM
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sperry sperry is offline
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Re: STi brakes, the brute force way!

Quote:
Originally Posted by sicksubie View Post
If you pay a shop to make these, please let me know as I will take a set as well (maybe defray the costs a bit). I have been looking at this specific problem recently and really like what you have come up with here...
I think for the cost to start being defrayed, I'm looking at having to make like 20+ adapters throught eMachineShop.com. That would probably get the cost down around $200 for the pair.

I just find it unlikely that I'd be able to get 10 people firm on dropping $1000+ to do this swap to justify putting down the money to have a bunch of these adapters made. I'd hate to spend $2000 and get stuck with 18 pairs of spare adapters.

But I'll look into it... maybe I can simplify the design enough to reduce costs or find a machinist in town here that would cut 6 or 8 of them for a few hundred bucks.
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Old 03-25-2010, 12:30 PM
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Re: STi brakes, the brute force way!

That emachineshop.com site is awesome. That opens up a lot of possibilities for a lot of things.
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Old 03-25-2010, 12:57 PM
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Re: STi brakes, the brute force way!

Quote:
Originally Posted by sperry View Post
I think for the cost to start being defrayed, I'm looking at having to make like 20+ adapters throught eMachineShop.com. That would probably get the cost down around $200 for the pair.

I just find it unlikely that I'd be able to get 10 people firm on dropping $1000+ to do this swap to justify putting down the money to have a bunch of these adapters made. I'd hate to spend $2000 and get stuck with 18 pairs of spare adapters.

But I'll look into it... maybe I can simplify the design enough to reduce costs or find a machinist in town here that would cut 6 or 8 of them for a few hundred bucks.
I should still have a set of front STi axles in my garage from when I did my 6spd swap.
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Old 03-25-2010, 06:24 PM
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sperry sperry is offline
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Re: STi brakes, the brute force way!

Just a minor update... if anyone was planning on building an adapter based on the posted plans... hold off a bit. I'm pretty sure the current position of the ball-joint will result in way too much negative camber due to a difference in length of the strut mounting arms on the two knuckles.

The good news is that it appears that the ball-joint taper is a standard 2in/ft taper (or 9.56 degrees) and I can get a reamer tool for it... they're just around $100 ... but that's still cheaper than an hour of labor at the machine shop and then I'll be able to make several adapters if I end up with an issue (like too much negative camber as described above).
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Old 03-25-2010, 10:54 PM
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Re: STi brakes, the brute force way!

Can you simply shorten the adaptor plate?
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  #13  
Old 03-25-2010, 11:23 PM
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sperry sperry is offline
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Re: STi brakes, the brute force way!

Quote:
Originally Posted by sicksubie View Post
Can you simply shorten the adaptor plate?
That's the basic idea... but I'm going to have to worry about interference with the control arm itself now...

Plus, there's the potential issue that the reduction in track width may result in steering geometry changes and make the car even more pushy. Or even worse, I may have an issue with strut clearance if higher offset wheels aren't used.

Really, I think I'm just going to have to make an adapter and both it all together and see where I end up, then revise things if my camber and track width are just too far off.
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Old 03-25-2010, 11:24 PM
Pegdrgr Pegdrgr is offline
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Re: STi brakes, the brute force way!

Being a shop that does up to 20K per month in parts from Subaru we get things at a great price too

I will PM you a price for the axles
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Old 03-29-2010, 09:19 PM
Johnybeas Johnybeas is offline
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Re: STi brakes, the brute force way!

interested, but what are the size differences as to trying to fit brembos or other STI brakes underneath some 17's???

sounds like a lot of work and hacking involved to make it work, we aught to see if we can't somehow get enough people together to get brembo or stoptech or another company to do a full big brake setup for the SVX. I think there are more and more of us every day who are modding for big power on the SVX
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