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EA82 - is there an upgrade for the master cylinder or vacuum booster?


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18 replies to this topic

#1 baccaruda

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Posted 30 July 2006 - 01:02 AM

well.. is there? :D

..
yes i searched.

#2 NorthWet

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Posted 30 July 2006 - 11:29 AM

What do you consider as "upgrade"? Nabco/Tokico makes a variety of master cylinders with diffeent bore sizes that could be used with some ingenuity, maybe even grafting the entire master/booster set form a Nissan/Toyota/et al.

#3 PoorManzImpreza

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Posted 01 August 2006 - 10:52 PM

I have a '90-'93 15/16 Legacy MC in my L series. The biggest FHI has for none ABS cars is 1" it was bolt on just swapped out the brake fluid level sensor between the two as the connector on the legacy is diff from the L-series. Very simple (well as simple as changing out a MC ever is) and my brakes have never felt better and this was swapping from a new 13/16+1" MC that come stock..brake booster swap wasn't required..
Oh and fyi just like the L-series the early Legacies had a hillholder so there's differences between the manual and auto MC..

#4 Ryanb

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Posted 02 August 2006 - 01:21 AM

Good info to know...thanks for the post guys

#5 baccaruda

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Posted 05 August 2006 - 12:11 AM

thanks.

#6 NoahDL88

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Posted 05 August 2006 - 12:33 AM

It occurs to me to urge caution, as a larger cylinder will move more fluid, but with less pressure, pascal's law is a hard and fast rule: pressure is = to Force/Area, if the force remains constant, at say 150 pounds, and you increase the area from 2 to 3, your pressure went from 75 down to 50. Laymans terms, you won't stop sooner, you'll stop later.


The only reason you'd want to go with a Legacy master cylinder, is if you went with the 5 lug swap and had legacy/XT-6/Impreza front calipers.

#7 Caboobaroo

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Posted 05 August 2006 - 11:42 AM

It occurs to me to urge caution, as a larger cylinder will move more fluid, but with less pressure, pascal's law is a hard and fast rule: pressure is = to Force/Area, if the force remains constant, at say 150 pounds, and you increase the area from 2 to 3, your pressure went from 75 down to 50. Laymans terms, you won't stop sooner, you'll stop later.


The only reason you'd want to go with a Legacy master cylinder, is if you went with the 5 lug swap and had legacy/XT-6/Impreza front calipers.


which is what I'm gonna use it for, hehe:brow:

#8 baccaruda

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Posted 05 August 2006 - 01:04 PM

Me too. I have XT6 front calipers and I have stainless steel brake lines. I will have to bench bleed my master cylinder and I was thinking in terms of squeezing in an upgrade while it's dry...

#9 NoahDL88

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Posted 05 August 2006 - 09:34 PM

I was just putting that out there, you guys know i'm the safety/seatbelt airbag nazi.

Didn't want some noob getting the wrong idea that it would make it better by increasing the master cylinder diameter.


Carry on.

#10 Gloyale

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Posted 23 January 2012 - 02:17 PM

I was just putting that out there, you guys know i'm the safety/seatbelt airbag ************.

Didn't want some noob getting the wrong idea that it would make it better by increasing the master cylinder diameter.


Uhh... have you done it?

I've driven an EA81 with a legacy master. Stops on a dime, way better than stock.

It does increase the "stiff" feel at the pedal.....Perhaps if there was no booster, and we were talking purely mechanical/hydrualic braking, your insight would apply.

But in a real world, with power assist, force required at the pedal is not a problem.

Bottom line, brakes feel tighter, and stop the car better. Espescially on a lifted rig.

#11 GeneralDisorder

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Posted 23 January 2012 - 02:36 PM

Hhhmmmm - maybe I'll try this on my lifted Hatch. We have that Legacy MC that Jacob used on his Brat for a short time.... but his brakes didn't work right before or after that was on it. Might be worth a second look.

I can see both veiwpoints - pressure at the pedal would have to increase to get the same force but the numbers might not be as drastic as what Noah is using. The pedal movement decrease might be worth the additional pressure requirement. I like a stiff pedal myself. And with rear discs that don't take as much pressure..... maybe.

Might try an EA82 turbo MC as well.

GD

#12 suberdave

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Posted 23 January 2012 - 06:49 PM

the way Pascal's laws work. with Hydraulic Principles if you increase the bore size on your MC you will decrease the pressure applied at your calipers. so unless you also increase your piston volume at your wheel cylinders or calipers, this will make brakeing more diffacult and will give you less brakeing power. however you will have to move the brake pedal less to move the brakes pads into contact with the rotors/drums.

however if you increase the piston size on your calipers, Say install dual piston calipers from a WRX onto your GL, but do not change your master cylinder you will have a very low pedal due to the fact that you will have to move the MC piston much more to move enough fluid to move the larger pistons...

i hope this makes since.

if not see this. http://www.engineeri...ascals-Law.aspx

-=Suberdave=-

#13 GeneralDisorder

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Posted 23 January 2012 - 09:30 PM

It makes sense for sure. But you still haven't provided any numbers. I haven't done the math either but what if it turns out that the additional pressure needed at the pedal is only like 10 lbs? That wouldn't be a problem for a lot of us.

Also - the common swap is to put EA82T discs on where the EA drums were before. How does the rear caliper piston size compare to the drum cylinder piston size? And how does that affect pedal pressure when combined with stock front brakes?

All conjecture without actual numbers. Have to go measure MC pistons, caliper pistons, and wheel cylinder pistons and run the actual numbers.

GD

#14 Turbone

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Posted 23 January 2012 - 10:06 PM

I put a early Legacy MC on my RX, running mid 90's Imp calipers on the front.
Suberdave is correct. I've noticed less pressure pushing the brakes but it takes more force to stop. I have a set of 2 pot WRX calipers that need rebuilding then they are going on, along with bigger rotors.

#15 suberdave

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Posted 24 January 2012 - 01:34 AM

All conjecture without actual numbers. Have to go measure MC pistons, caliper pistons, and wheel cylinder pistons and run the actual numbers.
GD


I will not argue with anyone on the internet, but it has been proven. it was done by Blaise pascal. it is called pascal's principle or pascal's law. it is the basics of everything to do with hydraulics.

GD i normaly agree with everything you say, but to say this is conjecture is like saying that gravity is conjecture unless you can see the numbers...

-=Suberdave=-

#16 Gloyale

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Posted 24 January 2012 - 03:05 AM

I will not argue with anyone on the internet, but it has been proven. it was done by Blaise pascal. it is called pascal's principle or pascal's law. it is the basics of everything to do with hydraulics.

GD i normaly agree with everything you say, but to say this is conjecture is like saying that gravity is conjecture unless you can see the numbers...

-=Suberdave=-


I don't think he's disagreeing with the law, Neither am I.

I think what he means, or at least what I meant.....is that with the small change in numbers, it adjusts the equation only a bit. Pedal travel is shortened, but pedal effort required to produce the same force at the wheels is still within the real of what a human and a Vac booster can do.

The resulting stiff pedal feels good to some types of drivers, and I think makes brakes quicker to respond, easier to modulate.

It's similar to a short shifter mod. Quicker shifts, but with less leverage requires a stronger hand. Some people like it, others find it rough.

#17 MilesFox

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Posted 24 January 2012 - 10:29 AM

I have an xt6 mc and booster in my 86 3door (yes it is xt6 5 lug with the option of moving to 2 pot calipers)

Since i used an xt6 booster, the rod on the back side was too long, and i had to shorten it (the xt has a deeper pedal box and more distance from the firewall to the trans shifter)

The legacy booster was the same diameter a the xt6's, but deeper and more protruding.

The car sems to stop well, although the rear wheel bearing is shot and the rotor is dragging (i am not actively driving this car)

#18 GeneralDisorder

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Posted 24 January 2012 - 12:30 PM

GD i normaly agree with everything you say, but to say this is conjecture is like saying that gravity is conjecture unless you can see the numbers...


I'm not saying that the law is conjecture. Certainly any changes made to the system will follow Pascal's law. What I'm saying is that the stock configuration is only one of many possible configurations that are acceptable (mathematically) and without doing the math you really don't know *how far* away from stock you have traveled with each change. Maybe it's a lot and it's not going to work - but maybe it's only a small amount and the net increase in required pedal pressure is both within the limitations of what the system can stand and within what a driver is capable of.

I still say - without numbers the qualitative statements to the effect of "It will not work" or "it works just fine for me" are not provable in any real sense. Pascals law is an immutable law of nature but without the numbers we don't fully know how his law effects what we are doing.

People have said "this is the law" and they have then jumped to "so you can't do it - because of the law!". Science doesn't work that way. You can't get to one from the other. The law only specify's how nature works - it doesn't specify if something is "good" or "bad" - that's subjective and we need more specific data to get a clear view of what constitutes good, bad, or otherwise.

GD

#19 renob123

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Posted 24 January 2012 - 12:59 PM

It's not a small change in feel going from an EA81 MC to a Legacy one. You may be able to get away with it with the stock engine, but it's outright dangerous on my Brat. The pedal feel never felt better, but not being able to stop really canceled that out.

Jacob




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