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Discussion Starter #1
hey guys, so i have an integra rear disc swap on my 94 EJ1 and have been running it successfully for about a year now, i got a 15/16" BB/MC combo, the 4040 prop valve and the trailing arms.

Yesterday i was out in the backroads fooling around and i hit my brakes "pretty" hard to come to a stop before hitting gravel. they worked just fine like they should have. I drive home and notice that my brake pedal felt a little different but didn't think much so i parked for the night and drove it today and the pedal almost sinks to the floor if applied slowly. i thought i needed to bleed them from when i changed the calipers so i go to check today and the fluid is spewing out of the little rubber "plug" diaphragm thing in the middle there. if you push the brakes and watch it, it gushes out, went through the whole reservoir in 1 day.

here is what i mean:


and here is a pic with out the plug:


does anyone know what this is for and why it blew? do i need a new valve or is something else the matter....maybe brake pedal adjustment?

Thanks for anything,
James
 

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^sounds plausible.

I don't know what that thing is but it looks like a "window" on mine not rubber. Definetly sounds like you need a new valve.
 

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BATSLOMAN GIVES NO FUCKS.
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sell ya a 40/40 valve 10$ plus shipping
 

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Discussion Starter #5
looks like i do need a new valve, luckily i have one on hand but i'm more interested in how it happened...i checked about 2 hours beforehand, drove it, hit the brakes hard, checked it again and it was 3/4 empty...

has anyone else had this happen? seems like a pressure relief of some sort... just want to make sure nothing else is wrong, but it had been on there for almost a year previously :?
 

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It is a type of pressure valve(though once open, stays open); the area between the two spools are obviously not meant to see much pressures if any at all; and when it does, it'll blow out that plug. I mean, there's like 2 o-rings on the spool that prevents pressurized fluid from even getting into that area.
 

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Discussion Starter #7
It is a type of pressure valve(though once open, stays open); the area between the two spools are obviously not meant to see much pressures if any at all; and when it does, it'll blow out that plug. I mean, there's like 2 o-rings on the spool that prevents pressurized fluid from even getting into that area.
interesting.... so did the prop valve just quit then? i was wondering why that was there initially, so every time i hit the brakes real hard the plug will pop out, even with a new prop valve?

that would be agitating..
 

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Discussion Starter #9
No no, pressurized fluid only gets in that area if one(or more) of those o-rings fail.
so say i replace the valve, and hit the brakes real hard, is it going to blow again? i would think not but curious...
 

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here is something to think about:

did the car that the 4040 come off of come with a 15/16 master cylinder? The valve might not have been built to tolerate the higher pressures attainable with the 15/16 MC.

But more than likely you just had a old valve with worn out seals.
 

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that doesn't make sense
 

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Smaller master cylinders output higher pressures(for larger slave cylinders).
lol yeah, no sense at all.


these failures seems to be rare, but not unheard of. i've sold so many (thats my pic you used up top....) but have only heard back from one person theirs failed.

the actual function of the prop valve is still a bit of a mystery, but i have reason to believe that rubber plug serves as a relief valve of sorts, or something like a "delay" in making sure the fronts get more pressure than the rears first, so the rears dont lock up sooner than the fronts. anyway, i havent taken the time to dissect and examine or put any more thought into how it all works.

but you just need a new prop valve. try to emulate the whole brake system to an OEM system as much as you can, is my advice.
 

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the actual function of the prop valve is still a bit of a mystery, but i have reason to believe that rubber plug serves as a relief valve of sorts, or something like a "delay" in making sure the fronts get more pressure than the rears first, so the rears dont lock up sooner than the fronts. anyway, i havent taken the time to dissect and examine or put any more thought into how it all works.
That makes sense! I took my proportioning valve apart a while back but don't know what I did with the spools. Though, the middle area seems like it works just as a balancer of some sort.

IIRC, the actual spool/valve for the rears are sprung also(I believe there was a larger spring that presses against both housing, then the smaller spring that goes between the spools). This may be for the knee point.
 

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Look at input and look at output.

For a given caliper piston(that's larger than the master cylinder), and leg force, you'd be able to exert more force onto the caliper with smaller master cylinder than a large one. You may also notice this in race cars that run booster-less setups(15/16 is considered large in these applications). Some other applications you guys may be familiar is engine lifts and jacks; the pump is a small cylinder while the rams are much larger; you have to pump a lot to displace enough fluid to fully extend those rams but it also takes much less effort than if you were to directly lift the engine or car.
 

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assuming this picture is accurate,



and knowing how one aspect of a prop valve SHOULD function, specifically the system is setup in diagonals, so if theres a leak in the right rear, the bottom half of the prop valve is going to get completely shut so the top portion can maintain pressure and give braking power to the right front and left rear. then i assume the springs in between the two halves only function as a 2 way check valve.

what this exactly has to do with the rubber plug i can only further assume, knowing that indeed the stock brake system has a delay for the rear brakes from empirical data taken with two pressure gauges, one at the front and rear corner. so i can only guess its the rubber plug that does that... its only a guess. how does it vary front vs rear when its only on the top? im not quite sure. and why only the top?

beats me. thats as far as i care at the moment.
 

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Look at input and look at output.

For a given caliper piston(that's larger than the master cylinder), and leg force, you'd be able to exert more force onto the caliper with smaller master cylinder than a large one.
opposite.

Pressure = Force / Area [oops, divide. eg. lbs PER sq inch]

really, this is simple.... you have this reversed in your head, or are simply failing to communicate. but what youre saying is just wrong.

if i can only guess your messed up thought process, youre thinking in reverse of the "pressure" at the caliper, but youre confusing pressure for force at the caliper piston. anyway, i dont have the patience to explain simple hydraulics.
 
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