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EA81 Master Cylinder/Booster Upgrade?

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I can't seem to slow my EJ-powered Brat as much as I'd like. I've asked around, and the consensus is that I should do the 5-lug swap, which I know I should do, but I can't finish it before the next rallyx. I've ordered the most aggressive pads I can find, and I'm looking into SS braided lines. The rotors are good, and the system has been recently bled.

 

I've searched pretty extensively, and I can't find anything about master cylinder/booster upgrades for EA81s. It looks like Legacy (and even WRX) parts will fit EA82s, but there's no indication of whether these will fit my Brat.

 

Has anyone had any luck with upgrading this part of the system?

 

Thanks.

 

Jacob

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I have a 99 outback master cly. on my hatch and its bolted to the stock brake booster its a great mod the pedal is as soild as rock

 

stock ea81 masters are 3/4 bore the ea82 is 13/16 legacy is 1 1/4 and outback is 1 3/4 or at least the one I have is 99 outback h6

 

i hope this helps they all bolt to the booster but I had to bend the lines a little bit

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I have a 99 outback master cly. on my hatch and its bolted to the stock brake booster its a great mod the pedal is as soild as rock

 

stock ea81 masters are 3/4 bore the ea82 is 13/16 legacy is 1 1/4 and outback is 1 3/4 or at least the one I have is 99 outback h6

 

i hope this helps they all bolt to the booster but I had to bend the lines a little bit

 

Woo! A response. And a useful one at that:)

 

Would upgrading the booster help?

 

Do you have any problems with the front/rear braking bias? Does one lock up way before the other?

 

Thanks.

 

Jacob

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on upgrading the booster you will have to find one that will fit it bolts to the pedal pod or is the mounting point of the pedal pod that said my guess would and ea82t booster if it mounts the same and the brake bais is the same and works just fine but our hatch doesn't have rear disks yet

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The rear will lock before the front unless you have a proportioning valve. More power (IE - larger bore MC) will cause this to happen with less pedal pressure - but still at the same relative braking strength.

 

I don't think a larger booster is really needed if you can bolt the larger MC to the existing booster. They both matter but the MC piston diameter matters more and the relative difficulty of fitting a larger booster vs. just bolting on a larger MC (since they are obviously easily availible) makes it less tempting to even want to mess with it. And if it later turns out that you need it you are already halfway there with the MC in place.

 

MC's tend to be pretty cheap in the aftermarket - you might just pick up a brand new one since now we know they fit. Brake lines can be cut, bent, coupled, and flared at will so that's not really an issue as long as it fits.

 

And - as we have talked about before - your MC is probably toast anyway.

 

GD

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The rear will lock before the front unless you have a proportioning valve. More power (IE - larger bore MC) will cause this to happen with less pedal pressure - but still at the same relative braking strength.

 

I don't think a larger booster is really needed if you can bolt the larger MC to the existing booster. They both matter but the MC piston diameter matters more and the relative difficulty of fitting a larger booster vs. just bolting on a larger MC (since they are obviously easily availible) makes it less tempting to even want to mess with it. And if it later turns out that you need it you are already halfway there with the MC in place.

 

MC's tend to be pretty cheap in the aftermarket - you might just pick up a brand new one since now we know they fit. Brake lines can be cut, bent, coupled, and flared at will so that's not really an issue as long as it fits.

 

And - as we have talked about before - your MC is probably toast anyway.

 

GD

 

That's what I was thinking with the booster, unless someone can come up with a reason why I definitely should change it. Rockauto has master cylinders in the $60-ish range.

 

I wonder if it's my wide tires that are helping me lock up the front first:)

 

Jacob

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I have a dual-stage booster from a Legacy on my EA82, along with a SVX M/C. The larger bore 1-1/8" SVX M/C actually decreases braking power in exchange for pedal firmness. The booster brings back the power, so now I have firmness and power.

 

I have WRX SS/teflon braided hoses, they work great too.

 

Sorry, I don't know it those will fit EA81 or not. Don't EA81 have a proportioning valve stock?

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I can see where higher speed capable rigs would really want to do this. good to know the EJ MCs fit... when I put together the braking system on my red brat, I put in a new EA81 MC, and used the hill holder, but split front/rear, with one hole plugged. and I'm running Toyota V6 calipers in front, and the stock Toyota drums in the rear, and it stops fine with my slightly larger :grin: tires...

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I can see where higher speed capable rigs would really want to do this. good to know the EJ MCs fit... when I put together the braking system on my red brat, I put in a new EA81 MC, and used the hill holder, but split front/rear, with one hole plugged. and I'm running Toyota V6 calipers in front, and the stock Toyota drums in the rear, and it stops fine with my slightly larger :grin: tires...

 

Nice. Did they fit on the stock rotors?

 

Jacob

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I have a 99 outback master cly. on my hatch and its bolted to the stock brake booster its a great mod the pedal is as soild as rock

 

stock ea81 masters are 3/4 bore the ea82 is 13/16 legacy is 1 1/4 and outback is 1 3/4 or at least the one I have is 99 outback h6

 

i hope this helps they all bolt to the booster but I had to bend the lines a little bit

 

Did you have any trouble getting the hardlines to fit the hole on the driver's side of the MC? Mine is right next to the strut tower. I bought some longer hardlines and bent them into place, but that one on the side was a pain.

 

Jacob

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They make right-angle fittings for places where the bend is too tight. Baxter's should have them.

 

GD

 

I saw some on Summit a few days ago. I couldn't tell from the picture if it would stick out too far. Too bad I don't have anyone to hand-deliver them from their warehouse anymore...

 

Jacob

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I saw some on Summit a few days ago. I couldn't tell from the picture if it would stick out too far. Too bad I don't have anyone to hand-deliver them from their warehouse anymore...

 

Jacob

 

Doh!

 

Makes a nice road trip though! :)

 

A1 coupling will have something.

 

GD

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I finally upgraded to an EJ 1-1/16" MC. had to bend my lines carefully by hand to clear the strut tower....

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A bigger bore master cylinder will not improve braking power. It will make the pedal engage higher and feel firmer, but the braking force at the wheels is reduced for the same pounds of pressure applied to the pedal. So you'll actually have to stand harder on the pedal to get it to stop as quick after "upgrading".

 

Master cylinder bore size is a balance. Go too small and the pedal will hit the floor before the brakes are at maximum clamping force. Go too big and you'll run out of leg strength before hitting maximum clamping force. Simple hydraulics, the piston ratio between the master and the wheel cylinders gives you the mechanical advantage.

 

A bigger or double diaphragm booster will give you higher braking pressures for the same pedal pressure because you have more assist. That can be a real upgrade to stopping power.

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I needed the volume because of the larger area at the calipers. Toy V6 calipers front, and Toy Supra disks in rear...

 

with the 13/16 MC, I had the soft pedal, and had to pump them to get full engagement brake power. Now, with the 1-1/16 MC, yes, I have a stiff pedal, but the stroke is less...

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In that case matching the master cylinder bore size to the bigger piston calipers makes sense because you're bringing the system back into range.

 

If you take a stock braking system and throw a bigger master on as an "upgrade", which many people do, then you end up with less braking power. That was my point, and as a caution to those who would go out doing just that and thinking the high-hard pedal was an improvement.

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I'm looking at Master Cylinders at Napa for a 99 outback to put in my EA81 brat.

 

Does the EA81 resivoir fit the outback MC?

Does with or without ABS matter?

 

Thanks!

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I'm looking at Master Cylinders at Napa for a 99 outback to put in my EA81 brat.

 

Does the EA81 resivoir fit the outback MC?

Does with or without ABS matter?

 

Thanks!

 

I can't speak to the first question. But the second, an ABS 4-cyl EJ master will be 1 1/16" bore with 2 ports. Non-ABS EJ will be 1" bore with 4 ports. FWD/non-ABS SVX master will be 1 1/16" with 4 ports.

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Either four port or 2 port works well 

http://www.ultimatesubaru.org/forum/topic/157224-i-just-upgraded-my-master-cylinderheres-what-i-found/

Check this thread out I did something similar.

Has anyone ever used SVX booster I might swap one of them I have into the car

to get more power, because eventually I will be using four pot front calipers.

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