Single diaphragm brake booster

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Ghost
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Joined: Sat Jan 12, 2013 5:20 am

Single diaphragm brake booster

Post by Ghost » Sun Nov 03, 2013 7:13 am

The changes this mod made were very interesting, and very positive.

Wheel and Brake setup:

Bridgestone Pole Position S04
RS 6 Spokes
FHI 4/2 pot 06 WRX calipers
Carbotech AX6 Pads
FHI 06 WRX rotors
StopTech Stainless Steel Lines
96' Impreza L ABS single stage booster.
Legacy SS stock master cylinder.

I liked the carbotechs when I installed them. They are a very grippy pad when bedded properly. But weeks after the install I was still having issues modulating pressure once I got them warmed up. It seemed like the kink point where more pressure equaled much more stopping was just around where the stock dual stage master changed modes.

This mod completely alleviated this problem. I mean gone, terminated, neck snapped IN HALF! The brakes feel just like how I want them to. Beautifully linear, not too much pedal travel to screw up downshifting. Downshifting while braking before was extremely tricky with sticky pads. Too much travel and too big of consequences for not keeping consistent pedal pressure.

I just have to recommend the list of brake mods I have done. It has completely woken this aspect of the car up. When you want to loose speed, you dump speed. It's incredibly easy to slow down too much. It makes it very tempting and possible to dive deep into corners with braking. I am done with modding the brakes for a long time. If I have heat problems I will go to DBA 5000 series rotors. I may add a driver controlled proportioning valve in the future.

The only downside has been the temperament of the pads. They need to be used hot every couple days. Prolonged cold braking will wear away the material off the rotor. This makes them squeal bad. If you really have to get on the brakes, ear splitting bad. But if you maintain a coating of friction material on the rotors they stay mostly quiet, maybe some squeaking when it is cold out, but easy to ignore.


-----------------------------


The Install.

I read a write up from an impreza forum the night before... while drunk. The author made this out to be some kind of big deal. Not really.

It requires a lot of brackets being loosened to move hoses and wires clear. I loosened my clutch mater cylinder to remove the booster, it was stuck until I did this. I wish I had started by doing this instead of trying to wrestle it out.

Installation really is the reverse of removal. Just a lot of step 1, step 2, step 3 stuff all around.

I recommend using the ATE super blue / type 200 fluids. One is blue, the other is gold, they both have the same properties. This allows you to see when you have completely flushed a system. Very useful for when your fluid is new and you want to make sure that you have completely bled out a line from the master cylinder down.

James614
Fourth Gear
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Joined: Sun Jun 10, 2007 4:35 am
Location: Arkansas

Re: Single stage brake booster

Post by James614 » Sun Nov 03, 2013 2:05 pm

So, what exactly does our stock booster do? Increase vacuum assist after a certain amount of pedal travel/pressure? I've always thought people went with the Impress boosters just because they offered less assist and more feel.
93 Touring Wagon (EJ20G 5spd Swap) -- Finally back and running strong as ever!

05 Outback 2.5XT 5spd -- Now the wife can have her SUV and get in on the turbo Legacy goodness at the same time.

Ghost
First Gear
Posts: 85
Joined: Sat Jan 12, 2013 5:20 am

Re: Single stage brake booster

Post by Ghost » Sun Nov 03, 2013 5:23 pm

James614 wrote:So, what exactly does our stock booster do? Increase vacuum assist after a certain amount of pedal travel/pressure? I've always thought people went with the Impress boosters just because they offered less assist and more feel.


I read the technical info so long ago that it has left my head. If somebody else can chine in, please do so. You will not be stepping on my toes.



On the stock dual diaphragm you push the pedal medium hard, it will travel to a point then stop. If you keep pushing harder it will keep moving, the force required to move it further increasing.

On the single diaphragm you push the pedal medium hard, it will travel to a point then stop. If you keep pushing harder it will move a tiny amount. So now you can really generate some breaking force with out the pedal sinking into the mush.

The overall feeling is that physically using the brake pedal is something that requires a lot less attention. It's quirks, like (okay I am braking really hard, I know my foot is going too low to blip the throttle) are no longer there.

Legacy777
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Re: Single diaphragm brake booster

Post by Legacy777 » Tue Nov 05, 2013 6:36 am

I changed the title of your thread because there is no dual or single stage boosters, there is only dual or single diaphragm boosters. This is a HUGE misconception among the Subaru community. I took apart a dual diaphragm booster about 9 years ago (wow that was a long time ago) and posted a lot of the technical info on NASIOC. This thread has a lot of info & pictures.

http://forums.nasioc.com/forums/showthread.php?t=672929

James, to answer your question, in short the single diaphragm booster provides less vacuum assist which eliminates that "dead area" at the top of the brake pedal stroke as well as makes the pedal easier to modulate. Another subie member and I tried using a regulator to limit the vacuum going to the booster to effectively do the same thing as the single diaphragm booster. It didn't work out too well because the regulator we used didn't react quick enough to the vacuum demands of the booster.

This thread has more info (don't mind my incorrect terminology)

http://forums.nasioc.com/forums/showthread.php?t=379541
Josh

surrealmirage.com/subaru
1990 Legacy (AWD, 6MT, & EJ22T Swap)
1997 Impreza OBS

If you need to get a hold of me please email me rather then pm

James614
Fourth Gear
Posts: 1744
Joined: Sun Jun 10, 2007 4:35 am
Location: Arkansas

Re: Single diaphragm brake booster

Post by James614 » Tue Nov 05, 2013 10:23 am

Thanks! That helps a lot. It also explains why my car seemed to have mushier brakes than a lot of other cars I've driven, despite having general strong brakes overall.
93 Touring Wagon (EJ20G 5spd Swap) -- Finally back and running strong as ever!

05 Outback 2.5XT 5spd -- Now the wife can have her SUV and get in on the turbo Legacy goodness at the same time.

Ghost
First Gear
Posts: 85
Joined: Sat Jan 12, 2013 5:20 am

Re: Single diaphragm brake booster

Post by Ghost » Wed Nov 06, 2013 9:29 pm

Hey Josh,

Cool link, thanks!

Legacy777
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Re: Single diaphragm brake booster

Post by Legacy777 » Thu Nov 07, 2013 6:56 pm

You're welcome.
Josh

surrealmirage.com/subaru
1990 Legacy (AWD, 6MT, & EJ22T Swap)
1997 Impreza OBS

If you need to get a hold of me please email me rather then pm

rallyak
Third Gear
Posts: 895
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Location: Anchorage,Alaska

Re: Single diaphragm brake booster

Post by rallyak » Fri Nov 15, 2013 6:48 pm

I'm getting ready to do this I was just wandering. I've read that some used abs boosters and others used non abs boosters is there a difference? Dose the car really know? I do have abs on my car and like to keep it.
Charles

90' White/Gray Outback DD workhorse (670,xxx) miles
92' Onyx Metallic (430,xxx) Wife's DD
68' Barracuda formula S 340 4spd coupe (ongoing project)
66' Mustang 2+2 4spd wife's (ongoing project)

Legacy777
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Re: Single diaphragm brake booster

Post by Legacy777 » Mon Nov 18, 2013 12:35 am

It doesn't matter whether the car has ABS or not. The booster is a pure mechanical component and the ABS electronics shouldn't really care one way or another.
Josh

surrealmirage.com/subaru
1990 Legacy (AWD, 6MT, & EJ22T Swap)
1997 Impreza OBS

If you need to get a hold of me please email me rather then pm

Ghost
First Gear
Posts: 85
Joined: Sat Jan 12, 2013 5:20 am

Re: Single diaphragm brake booster

Post by Ghost » Sat Nov 28, 2015 10:00 am

Still really digging this, it is a must do mod. If I ever 'upgrade; to a GC chassis this is coming with me.

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