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Old 05-28-2009, 12:13 PM   #1 (permalink)
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Default STi Brake Booster Swap... A MUST DO!!!

So after an STi master cylinder, SS lines, Superblue fluid, front Brembos, rear H6, and HP+ pads I still wasn't happy. There were several times when the pedal had NO feedback at all. The only thing that the mush could be was either the lack of a rear Brembo kit (~$800) or the brake booster (used, $37.50 shipped). So, I bit the bullet and swapped in an '05 STi booster I bought off NASIOC.

Holy mother of crap! Night and day... If you drive hard or you've done a brake swap, you must to do this. Some people say that it doesn't do anything for performance, only pedal feel. Well, they haven't had their setup hit the floor then.

Yeah, it's a major PITA... but you simply have to do it. I had already swapped my master cylinder and bled it with fresh Superblue fluid so I didn't want to take it out. I was able to the swap WITHOUT taking it back out. Once it's unbolted it will move out of the way enough. There really isn't a trick to this... It's about as labor intensive (and rewarding) as swapping over a steering rack. A solid 3-4 hours if you know what you're doing.

Here are some tips...
-You need to put the actuator arm back over the brake pedal arm and put the pin in before you tighten down the booster to the firewall. If it's not on you won't be able to push the rod in enough to bring it down/around/on. That'll make sense when you're doing it.
-I siphoned the fluid out of and removed the clutch reservoir for more room. Just don't hit the clutch pedal with it off and you can reattach and fill the reservoir when you're done. No bleeding required.

That's pretty much it... If something seems to be in the way take it off. Off the top of my head, I removed the TMIC, air pump, a few vacuum lines, the TMIC mounting arm, and a bracket that holds a silver tube to the firewall.

Good luck! Go do this!
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Old 05-28-2009, 12:18 PM   #2 (permalink)
 
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This is solid info. I know of a local on 6/4's and a stock m/c and booster. I will pass it along.
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Old 05-28-2009, 12:20 PM   #3 (permalink)
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Hmm... I'll add this to my list of mods to do next spring, right after the "MY04 STi steering rack assembly"
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Old 05-28-2009, 12:22 PM   #4 (permalink)
 
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I would like to rock the new rack but im to lazy to install one.
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Old 05-28-2009, 12:34 PM   #5 (permalink)
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mmTasty, can you post a pic of what you actually installed? I bought this off of a 2007 Impreza WRX STi, and I'm not quite sure which is the master cylinder and which is the brake booster...



Mine looks like there were wires cut too. Is this going to be a problem?
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Old 05-28-2009, 12:58 PM   #6 (permalink)
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brake booster is the black circle part, MC is the brake fluid bottle + the silver cylinder

think stock brakes would benefit from just a MC + BB upg?
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Old 05-28-2009, 01:54 PM   #7 (permalink)
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Quote:
Originally Posted by yuephoria View Post
mmTasty, can you post a pic of what you actually installed? I bought this off of a 2007 Impreza WRX STi, and I'm not quite sure which is the master cylinder and which is the brake booster...



Mine looks like there were wires cut too. Is this going to be a problem?
You'll want to swap in that entire thing. Neoshi is correct BTW. If there's a plug plugged into the MC and cut, you're fine because your Forester's plug and wires are what you'll be plugging in. Also, it may help to pull the MC off the booster to get it all in. There are two silver nuts holding it on. There won't be any fluid to worry about when splitting them. A side note about the MC, "bench bleeding" is done with the MC IN the car... All it entails is taking some hose and looping it back into the reservoir and pumping a few times before you attach the lines. Really easy...

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brake booster is the black circle part, MC is the brake fluid bottle + the silver cylinder

think stock brakes would benefit from just a MC + BB upg?
Absolutely. When I swapped in the Brembos, slotted rotors, STi MC, SS lines, H6, and pads I noticed a difference... when I put the booster on I noticed a BIG BIG BIG BIIIIG difference. So what's worth more and what comes first? I don't know... All I know is the order in which I did mine. Depending on what you're going for, a big brake kit may be a total waste. SS lines, ATE fluid, HP+ pads, STi MC, and STi BB should be all you'll ever need. With those changes, unless you're racing your Forester on a track, you should never need more.
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Old 05-28-2009, 06:19 PM   #8 (permalink)
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Is the volume of the sti booster larger than ours too?

I need to flush my brake fluid soon anyway. I think i have over 20 autox's on it plus a winter since my last flush. If i can pick one up for $40 + an afternoon of labor i'll be happy to do it.
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Old 05-29-2009, 07:06 AM   #9 (permalink)
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You do NOT need to bleed your brakes to swap the booster. The MC will detach and move out of the way far enough.

I don't know what's exactly mechanically different. The size and shape are identical. The STi one is less effected by vacuum somehow. Maybe I'll rip open the stocker and see what makes them go. Maybe there will be an easy way to deactivate the hyper action...
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Old 05-29-2009, 07:13 AM   #10 (permalink)
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Quote:
Originally Posted by Duderotomy View Post
Hmm... I'll add this to my list of mods to do next spring, right after the "MY04 STi steering rack assembly"
Quote:
Originally Posted by Tuned200 View Post
I would like to rock the new rack but im to lazy to install one.

The booster and steering rack are both upgrades that 5' into the test drive you'll wish you had done them sooner. Especially if you're doing autoX or track days.... Seriously major improvements at a somewhat low cost.
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Old 05-29-2009, 07:37 AM   #11 (permalink)
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awesome! I'm so glad someone tackled this.

i've been saying this all along. You can do whatever you want to the rest of the braking system on a Foz, but until you swap the BB, the brakes will still be less than optimal in feel and performance.

What mmtasty is saying is backed up in the numbers too. The line pressure differences (at two different braking forces) are way different on the STi booster vs. the rest of the impreza lineup.
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Old 05-29-2009, 08:46 AM   #12 (permalink)
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dang it! I was always told that the BB from the sti was the same as ours. I guess you can't believe everything you read on the interwebz. When I bought my STI MC on ebay, it came w/ the BB, but I told him not to ship the BB to save on shipping. I feel retarded now.
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Old 05-29-2009, 08:51 AM   #13 (permalink)
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I will be doing this mod soon (already got the MC). Any step by step instructions (ala scoobymod style)?
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Old 05-29-2009, 08:57 AM   #14 (permalink)
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How can I tell that the BB and MC are from an STI? I have a set sitting around here and I know the BB is supposedly off an STI, but I'm not sure about the separate MC that came with it. Are there any visual clues or markings that set it apart from the Forester ones?
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Old 05-29-2009, 09:47 AM   #15 (permalink)
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STI MC had the mark 1 1/16 underneath, Forester one just stamped 1.
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