4/2-Pot Brake Discussion

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Legacy777
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4/2-Pot Brake Discussion

Post by Legacy777 »

I'm retitling my previous WTB thread since it turned into more of a technical discussion about the 4/2-pot brakes.
Josh

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originalcyn
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Re: WTB 4/2-pots

Post by originalcyn »

I'm still in the middle of the process with mine. They're all cleaned up for the most part and powdercoated, but they have to go back together and i'm kind of nervous to try.
Kijan

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Re: WTB 4/2-pots

Post by Legacy777 »

Did you disassemble the two halves or just pull out the pistons & boots?
Josh

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Legacy777
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Re: WTB 4/2-pots

Post by Legacy777 »

Thanks for the links!

I would recommend cleaning any powdercoating off the mating surfaces of the calipers.
Josh

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Re: WTB 4/2-pots

Post by NICO »

1993 Subaru Legacy 44B STi 4Cam 16Valve Turbo Intercooled AWD
EJ22T, STi EJ207 DOHC, Vi-PEC (Spare Autronic) @ 426.20HP / 394.94ft lb @ 00psi
Tuned By: Franz Diebold ( DIEBOLD AUTOSPORT ) @ NVauto
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Re: WTB 4/2-pots

Post by Legacy777 »

Nico,

Any reason why I should get those vs. keep the stock ones? I've already purchased the stock seal kit.
Josh

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originalcyn
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Re: WTB 4/2-pots

Post by originalcyn »

It comes up pretty frequently, but the stock pistons seize somewhat often. The thought is dissimilar metals apparently or something along those lines. The stainless pistons replacement, while expensive, supposedly makes it less likely that the pistons will seize or rust in the long run. i'm uncertain as to whether or not this only affects the JDM 4 pots, or if the 06/07 wrx 4 pots are also affected. Also, i don't think the stock reseal kit comes with the grommets/orings that go between the two halves. This isn't really an issue if you reuse them, but people do like to replace them.

Interesting to note, the parts for the 4 pots are shared with one of the 300zx 4 pots, so kits are often interchangable.

Thanks for the tips Josh. I cleaned off the mating surfaces already, but am curious about the black covering that's on them? like, a layer of paint or something, i'm not really sure. Is it bad if it gets scratched at all?

There's also a number of 4/2 pot restoration posts on the forester forums Josh, if you're wanting some more information on it.
Kijan

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Re: WTB 4/2-pots

Post by Legacy777 »

Kijan,

Thanks for the info on the piston's seizing...that's definitely interesting to know. Can I buy just the SS pistons without the seals since I already bought those? I really haven't started looking at the calipers yet, so I need to do that first to see their condition.


Regarding the black cover, I really didn't get a good look, do you have any better pics you can share?


I'm going to split this thread so the technical discussion is in the tech forum.
Josh

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Re: 4/2-Pot Brake Discussion

Post by SILINC3R »

I know Subaru sells the pistons or at least they do for the 4th gens Legacy. Replacing the seals is quite fun once you get the hang of it. Youtube came to the rescue for me. I had to replace each piston seal one at a time. It can be kind of dangerous as you use air to push the piston out of the bore. Not much psi is required just a good seal of the air chuck to the brake line opening.

In regards to the rust issue remember that brake fluid is hydroscopic, absorbs moisture. That is the main reason they rust and why fluid should be changed yearly. Of course the dust boot tearing wont help anything haha
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Re: 4/2-Pot Brake Discussion

Post by Legacy777 »

The pistons were already out on mine, so I'll check them out and make the call from there.
Josh

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Re: 4/2-Pot Brake Discussion

Post by originalcyn »

The pistons on the set I bought from drew were pretty pitted, but he was awesome and bought me a replacement set of pistons.
Kijan

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Re: 4/2-Pot Brake Discussion

Post by MConte05 »

For anyone planning on rallying with these. Make sure you have gravel scrapers on the rear, and make sure they work perfectly. I lost my brakes on stage at LSPR because the rear aluminum calipers got worn down to the crossover pipe, causing all the fluid to take a hike.

When I got back, I found the other side just barely hanging on too. Since I don't want to replace these things yearly, I've just decided to go back to stock leggy turbo calipers and vented disks.
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Re: WTB 4/2-pots

Post by originalcyn »

Legacy777 wrote: Regarding the black cover, I really didn't get a good look, do you have any better pics you can share?
Josh,

Sorry it took forever to get back to you on this. Here's what i mean:

Image

I think it's just paint...but i'm not sure honestly. It's a little scuffed at this point.
Kijan

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Re: 4/2-Pot Brake Discussion

Post by BoneIslandScooby »

Josh, I'd love to hear your take on the setup that's going on my car, since you put up all that brake math in the past. I've got the whole Nissan 300ZX setup for the front and rear. I'm using the front caliper brackets from KNS and the rear caliper brackets from Godspeed. The rotors are stock style Brembo blanks for the front and budget brand 2006 - 2007 WRX rear rotors, both sets of calipers were bought from BMA Parts. I got premium (non-performance) ceramic pads for the front and Hawk HPS for the rear. I figured with the increase in rotor size in the front that I'd have to shift some of the bias to the rear with the high performance pads. I could give this setup a HUGE upgrade in the future by replacing the rotors with high performance parts with slots and better metallurgy. In the meantime, I think it's a HUGE upgrade for not too much money.
Last edited by BoneIslandScooby on Sat Dec 20, 2014 12:03 am, edited 1 time in total.
Legacy777
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Re: 4/2-Pot Brake Discussion

Post by Legacy777 »

Assuming the 300ZX setup is pretty much the same as the 4/2-pots and you started with the turbo Legacy brake setup, then the 4/2-pots shift brake bias rearward. I would recommend running the same type of pads front and rear to start out with. If you feel that you have too much front or rear bias you can try adjusting the pad compound from there.

Regarding the rotors, different rotors don't add "performance". At best different rotors (slotted, drilled, different internal cooling vanes) provide a means to help control temperature of the rotor and maybe help the brake pad from becoming glazed. For the money, standard blank rotors are fine and if you want to do anything to them, get them cryo-treated so they are more durable and hold up to increased temperatures and heat cycling.
Josh

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BoneIslandScooby
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Re: 4/2-Pot Brake Discussion

Post by BoneIslandScooby »

Actually, I forgot to mention in my original post that the front rotors are the bigger diameter 316 x 30 mm thick rotors from the 2005 + Legacy GT as opposed to the 294 x 24 or 295 x 25.5 front rotor from the WRX. That's why I felt that I needed to shift some of the brake bias to the back with dissimilar pads.

Who does this cryo treating?
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Re: 4/2-Pot Brake Discussion

Post by jamal »

Yeah the Z front brakes use a bigger rotor and a different mount. But there is an adapter from KNS brakes to use an LGT front rotor.

Brake bias with the 300z calipers, 316mm front rotors, and 290mm rear rotors should be REALLY close to stock bias, and will be farther forward than just using Subaru 4/2 pots, which work fine and don't require any special pad compounds. Only thing you'll need are wheels that clear them.

Centric/stoptech does cryo treating. I'm not sold on the value of them (they cost more, but last longer), it might even out over getting standard cheap rotors. I also like stoptech's street performance pads.
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Re: 4/2-Pot Brake Discussion

Post by BoneIslandScooby »

I can't wait to put them to good use. 17x8's with a 48mm offset should clear I imagine.

I had to edit it after I looked them up.
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Re: 4/2-Pot Brake Discussion

Post by Legacy777 »

Just looked at the percentages and with the LGT front setup & 2-pot rear it's 4.1% forward over the stock turbo Legacy setup. As Peter (Jamal) mentioned you shouldn't need any type of special pad compound.

Regarding cryo treating, I think some of it depends too on the car/mods, driver, and how the car is driven. I always seemed to have issues with my Legacy. I'm not sure if that was due to the original size of the rotors, my driving style or what. I had my most recent set of rotors cryo treated by a place in Washington that unfortunately is no longer around. They were called One Cryo. I don't know if all the places out there did the same "deep cryo" treating that they advertised. Here is a blurb from their website curtesy of the internet archive (I love that thing!!)

https://web.archive.org/web/20060211015 ... yo/how.htm

It may be a wash in costs, but again I do think it depends on how you drive the car. If you aren't pushing the brakes hard, then regular rotors are probably fine.
Josh

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Re: 4/2-Pot Brake Discussion

Post by jamal »

Legacy777 wrote:Just looked at the percentages and with the LGT front setup & 2-pot rear it's 4.1% forward over the stock turbo Legacy setup. As Peter (Jamal) mentioned you shouldn't need any type of special pad compound.
4-pots I think have smaller pistons than the LGT caliper, so it will be less forward than that.

Yeah I never had problems with rotors. Right now I've been on the same set of centric blanks and stoptech pads for like 5 years and they are smooth and have good life left. Although they are WRX/H6 sized on a non-turbo car.
Legacy777
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Re: 4/2-Pot Brake Discussion

Post by Legacy777 »

Yes, the 4-pots have smaller pistons (at least according to the FSM) than the LGT calipers. That 4.1% includes that.

You can play with the different caliper combos with my brake math spreadsheet.

http://main.experiencetherave.com/subar ... kemath.xls
Josh

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Re: 4/2-Pot Brake Discussion

Post by jamal »

Brake spreadsheet is awesome. I use it all the time.
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