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EA81 Master Cylinder/Booster Upgrade?


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19 replies to this topic

#1 renob123

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Posted 02 June 2010 - 11:31 AM

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

#2 84gl

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Posted 03 June 2010 - 10:15 AM

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

#3 renob123

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Posted 03 June 2010 - 10:19 AM

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

#4 84gl

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Posted 03 June 2010 - 10:25 AM

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

#5 GeneralDisorder

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Posted 03 June 2010 - 05:42 PM

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

#6 renob123

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Posted 03 June 2010 - 05:52 PM

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

#7 presslab

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Posted 10 June 2010 - 11:04 AM

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?

#8 GeneralDisorder

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Posted 10 June 2010 - 12:35 PM

Don't EA81 have a proportioning valve stock?


EA81's do not have any sort of proportioning system unfortunately.

GD

#9 VaporTrail

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Posted 10 June 2010 - 10:33 PM

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...

#10 renob123

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Posted 10 June 2010 - 11:26 PM

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

#11 GeneralDisorder

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Posted 10 June 2010 - 11:34 PM

Mick is running Toy suspension, etc. I doubt they would come anywhere close to fitting a Subaru suspension.

GD

#12 renob123

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Posted 22 June 2010 - 11:32 AM

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

#13 84gl

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Posted 23 June 2010 - 06:20 AM

It was a real pain but finally gave in and i used the stock lines

#14 GeneralDisorder

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Posted 23 June 2010 - 10:37 AM

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

GD

#15 renob123

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Posted 23 June 2010 - 10:43 AM

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

#16 GeneralDisorder

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Posted 23 June 2010 - 11:24 AM

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

#17 VaporTrail

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Posted 17 September 2012 - 04:44 PM

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

#18 WoodsWagon

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Posted 19 September 2012 - 02:57 AM

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.

#19 VaporTrail

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Posted 19 September 2012 - 09:36 AM

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...

#20 WoodsWagon

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Posted 20 September 2012 - 10:39 PM

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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