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WRX mastercylinder in an EA82?


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17 replies to this topic

#1 Caboobaroo

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Posted 12 January 2005 - 03:11 PM

Well since I'm doing all these lovely upgrades to my RX and brakes and suspension are one of them, I was wondering if a WRX mastercylinder would fit into it as well? Anyone know?

#2 carfreak85

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Posted 12 January 2005 - 06:28 PM

I don't know, but don't put a WRX master cylinder in your car just to say you have one. Unless they have the same bore diameter, it will severly screw up your stock brake bias and make your brakes very poor in general.

#3 Legacy777

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Posted 12 January 2005 - 09:18 PM

The MC will not affect bias in any way. A larger/smaller MC will affect pedal travel mostly, and feel slightly.

To answer your question, more then likely the WRX will not work. Where do the brake lines come out on your current MC? To the side and to the bottom? Do you have ABS? If you have ABS, you probably have them only to the side.

If you have upgraded to larger calipers, and are having issues with pedal travel being too much, you could probably upgrade to a legacy MC.

If you can give me some more details on your current setup, and what you want to change, I can help you size things properly. I've essentially redesigned my entire brake system. The only thing left stock is the hard lines.

#4 JWX

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Posted 12 January 2005 - 10:05 PM

can you post the info? I'd love to read it

#5 NoahDL88

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Posted 12 January 2005 - 10:26 PM

i believe that a larger master cylinder will reduce stopping power, bigger area pushed reduces the multiplication, so if you go to a bigger bore, the brakes will be less effective.

#6 ballitch

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Posted 12 January 2005 - 11:32 PM

that is true but you will have more brake fluid flow, so if you upgraded to a higher piston caliper count (2 vs. 4), brake fluid dynamics can get pretty complicated.

#7 Caboobaroo

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Posted 13 January 2005 - 08:43 AM

ok here's what I'm planning on doing to my setup right now. I am putting XT6 brakes on it but I plan on upgrading to a drilled rotors from a Legacy since I believe they'll fit along with some upgraded calipers. I saw a gen 1 Legacy in a U-Pull-It in Oregon that was done up by RalliTek with 2 pot calipers and I was planning on doing the same. Along with this, I'm adding stainles steel brake lines as well. This is why I asked if the WRX or even a Legacy MC would work. I haven't look at the MC on the RX yet but I will get back to you as soon as I find out where the lines come out from. Even if it they don't come out the same direction, I can make new hardlines pretty easily:D

#8 Legacy777

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Posted 13 January 2005 - 09:27 AM

i believe that a larger master cylinder will reduce stopping power, bigger area pushed reduces the multiplication, so if you go to a bigger bore, the brakes will be less effective.


This is sort of true. You are correct in saying that output pressure of a larger bore MC will be less with a known input force, when compared to a smaller bore MC with the same known input force.

As far as saying the brakes will be less effective, I'll have to disagree with that. Almost all, if not all production cars have over boosted brakes, especially the newer 90+ subarus. The older ones may not be as bad, but the brake booster still provides plenty of assist. The end result would actually be a better feeling brake pedal. A side benefit would be brake lockup would require a more pedal force, which is usually good.

#9 Legacy777

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Posted 13 January 2005 - 09:29 AM

that is true but you will have more brake fluid flow, so if you upgraded to a higher piston caliper count (2 vs. 4), brake fluid dynamics can get pretty complicated.


You really don't have to worry about any fluid dynamics. The main thing you need to take into consideration when swapping calipers is volume requirements. How much fluid are these calipers going to use compared to my old ones. If it is a small amount, you can probably get away with leaving your MC alone. However if volume requirements increase enough, a larger bore MC is needed to meet those volume demands.

#10 Legacy777

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Posted 13 January 2005 - 09:36 AM

ok here's what I'm planning on doing to my setup right now. I am putting XT6 brakes on it but I plan on upgrading to a drilled rotors from a Legacy since I believe they'll fit along with some upgraded calipers. I saw a gen 1 Legacy in a U-Pull-It in Oregon that was done up by RalliTek with 2 pot calipers and I was planning on doing the same. Along with this, I'm adding stainles steel brake lines as well. This is why I asked if the WRX or even a Legacy MC would work. I haven't look at the MC on the RX yet but I will get back to you as soon as I find out where the lines come out from. Even if it they don't come out the same direction, I can make new hardlines pretty easily:D


Are the XT6 calipers 2 pot calipers? Are you current calipers single pot calipers? Do you or anyone have any information regarding piston sizes of the calipers for your car and the XT6, and possibly MC bore sizes? If you have all that info, it's pretty easy to come up with an answer whether you need to mess with swapping your MC or not.

Does your car have the same bolt pattern as the Legacy? I'd also recommend against cross-drilled rotors. I wrote up this article a while ago, but the information in it is still good
http://www.surrealmi...aru/brakes.html

Here's a excel spreadsheet with some sizing info on calipers, MC's, etc that I created when I was trying to figure out what to swap over on my brake work.
http://www.main.expe...o/brakemath.xls

#11 Caboobaroo

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Posted 13 January 2005 - 10:15 AM

well the XT6 and EA82 calipers are single pot calipers but I have seen aftermarket 2 pot Legacy calipers. Yes the Legacy bolt pattern is the same as an XT6, 5x100.

ery well written, I had no idea that they would suck that much compared to OEM ones. I knew that they would be able to warp a little easier due to the amount of rotor to pad contact they make thus making more heat into less metal. You should put that in the USRM for everyone to read.

Thanks guys for the input, keep it coming, I want opinions on doing this setup!

#12 subarubrat

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Posted 13 January 2005 - 10:49 AM

Anyone know if the XT6 or other calipers will mate up to an EA81 car? Are these of a larger pad area, different piston config? Anyone ever tried EA82 disks and calipers on an EA81?

I haven't touched much EA82 stuff and I am looking to increase the brake heat capacity on the BRAT.

#13 JWX

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Posted 13 January 2005 - 12:45 PM

I'd go complately aftermarket, go with who ever you like brembo, wilwood, whatever. but thats me ;)

#14 archemitis

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Posted 13 January 2005 - 04:09 PM

Well since I'm doing all these lovely upgrades to my RX and brakes and suspension are one of them, I was wondering if a WRX mastercylinder would fit into it as well? Anyone know?

i have loads of stopping power with just 4 disc brakes. get that rx DRIVING, and try out the brakes. no need to upgrade. if it doesnt work great, flush the lines, new pads and rotors, and your set.
in my experience master cylinders arent gonna give you any more stoping power. just more pistons in your calipers

untill you get tires the size of subarubrats the 4 disc works great.

#15 Caboobaroo

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Posted 13 January 2005 - 04:42 PM

ummm I had it driving and tried the brakes out BUT I'm upgrading to the XT6 stuff for my 5-lug. I'm planning on flushing my whole system once its all in there but with making power, you need to get it to stop as well. One reason I'm asking this question is because I can get one for pretty reasonable so I was going to try and make it work if it was possible.

#16 Legacy777

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Posted 13 January 2005 - 07:01 PM

I'd definitely agree with archemitis, get the car going/running, see how the brakes are, and go from there.

I actually had a pretty good brake setup on my stock legacy brakes. I ran performance friction carbon metallic pads. These things were great pulling the car down from higher speeds.

The main drawback from the stock setup was the rotors were too small and just couldn't sink, and dissipate heat fast enough. Looking back at things now, cryo-treated rotors probably would have helped the rotors last longer.

#17 subarubrat

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Posted 14 January 2005 - 08:36 AM

I'd go complately aftermarket, go with who ever you like brembo, wilwood, whatever. but thats me

Believe me a third of that truck is aftermarket. The problem remains that I would like to know the basic series compatability for fitment. For example, will legacy/outback calipers mate up on the stock EA81 hub? Has anyone retrofitted newer calipers to older hubs? Rotors? Once I know say gen I impreza calipers fit I can go get the aftermarket I want.

#18 JWX

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Posted 14 January 2005 - 10:25 PM

Believe me a third of that truck is aftermarket. The problem remains that I would like to know the basic series compatability for fitment. For example, will legacy/outback calipers mate up on the stock EA81 hub? Has anyone retrofitted newer calipers to older hubs? Rotors? Once I know say gen I impreza calipers fit I can go get the aftermarket I want.

you have a very good point there. but I don't think anybody has, if I had a set of calipers I'd try them on my hatch. but alas I don't, but I might know somebody who does :)




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