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STI Master Cyl. and Brake Booster SWAP SUMMARY for LGT


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  • 10 months later...

I am going to be doing this upgrade in the next couple of weeks. I am already replacing my calipers, rotors and pads so I figured I may as well do this upgrade while I'm at it to save on having to bleed the lines more than once. If you are curious, this is the setup that I am going with for calipers, rotors and pads.

 

I am also going to pickup the Grimmspeed Master Cylinder Brace. I know my brake lines aren't not in very good shape so I may as well look into some SS lines as well. I do not want to make a mistake and get the wrong parts so if anyone has a link they can give me to the correct SS lines it would be greatly appreciated.

 

Also, looking on ebay for the STI MC and Brake Booster came up with a few options:

This one.

and

This one.

 

Do those both look like the right part? I am planning on doing my ordering today or tomorrow so I am just trying to make sure I get the right parts.

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  • 2 months later...
Just wondering if anyone has done this swap with a VDC equipped car? If so, could anyone comment on exactly how they adapted the 12mm flare nut to the 10mm flare nut on the hard lines from the mc to the ABS controller? Thanks!
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  • 3 months later...

Can someone confirm or deny that v7 sti mc and booster will fit an 08 LGT with 6 speed sti trans? (trans shouldnt matter but). Cannot find an 04-05 sti used mc and booster, but on ebay the version 7s are plentiful. Planning on doing this with the ATS brembo upgrade in the next few weeks.

 

Thanks in advance, sorry for the old thread bump

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Been awhile since I went through the entire thread, but is there any reason you could not mount the STI MC itself to the Legacy booster? Believe the larger bore (17/16") MC is where the real difference lies.

Different booster thickness/power, bolt-mismatch???

- Pro amore Dei et patriam et populum -
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  • 2 months later...

hey all, quick question.

 

I just went through the whole process for swapping my Booster/MC and got everything put back together, started the engine and the brake pedal has practically no resistance. It does not sink to the floor or move on its own however.

 

With the engine off after 3-4 presses the pedal is rock solid. I bench bled the new MC, pressure bled all 4 calipers, measured and matched the brake clevis to the old booster, and inserted the check valve (bullet side towards the intake/flat side towards BB and firewall).

 

kind of at a loss here. If anyone has any ideas, I would appreciate it.

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It has been a while since I did this mod, but I'd like to help if I can.

Did you use the STi or the WRX MC (booster is the same)?. The WRX is the 1" and the STi is the 1 1/16". I tried the STi first in my struggle, and it was awful. Like you describe with the rock solid pedal when engine off. Honestly, if you are using the STi MC, my advice is to drop it and get one from a WRX.

Could you describe a little more what it is doing when engine running?

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It has been a while since I did this mod, but I'd like to help if I can.

Did you use the STi or the WRX MC (booster is the same)?. The WRX is the 1" and the STi is the 1 1/16". I tried the STi first in my struggle, and it was awful. Like you describe with the rock solid pedal when engine off. Honestly, if you are using the STi MC, my advice is to drop it and get one from a WRX.

Could you describe a little more what it is doing when engine running?

 

Appreciate the response. I am using an 06 STi BB/MC so the 1 1/16" bore. With the engine running the pedal loses almost all pressure. With the car lifted, the brakes do stop the back wheels at the very bottom of the pedal travel. The pedal feels monumentally worse than stock LGT setup (or any car with properly functioning brakes), but it doesn't feel like the pedal is disconnected or sinking into the floor or anything.

 

There are no apparent leaks anywhere, fluid level stays constant in the reservoir, no puddles or wet spots. Put about 2L of brake fluid through the system and getting clear fluid with no air bubbles in any of the lines.

 

This whole job has been a pain in the ass every step of the way so it has me second guessing if I messed something up along the way. It's possible that the STi MC will still be too mushy for me after its all working, but this definitely feels like something wrong rather than another poorly performing MC.

 

My best guess is there is some significant amount of air still trapped in the MC or elsewhere. I probably did not do a fantastic job bench bleeding...

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Appreciate the response. I am using an 06 STi BB/MC so the 1 1/16" bore. With the engine running the pedal loses almost all pressure. With the car lifted, the brakes do stop the back wheels at the very bottom of the pedal travel. The pedal feels monumentally worse than stock LGT setup (or any car with properly functioning brakes), but it doesn't feel like the pedal is disconnected or sinking into the floor or anything.

 

There are no apparent leaks anywhere, fluid level stays constant in the reservoir, no puddles or wet spots. Put about 2L of brake fluid through the system and getting clear fluid with no air bubbles in any of the lines.

 

This whole job has been a pain in the ass every step of the way so it has me second guessing if I messed something up along the way. It's possible that the STi MC will still be too mushy for me after its all working, but this definitely feels like something wrong rather than another poorly performing MC.

 

My best guess is there is some significant amount of air still trapped in the MC or elsewhere. I probably did not do a fantastic job bench bleeding...

It sounds like the brake booster is bad.
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  • 2 years later...
  • 2 months later...
I use a Motive power bleeder on mine and follow the manual for the sequencing. Pedal is always firm with nearly no (<3/8") of yield before it gets very firm and stays that way through the stroke. Modulation is linear and braking is very right now. Not E26 M5 right now, but close IME.

 

Centric Premium rotors, with bedded-in Hawk HPS performance pads, on stock calipers with Stop Tech SS Lines are at all four corners. The GS MC brace is installed and I've never felt the need to upgrade to anything beyond this stage.

 

I've not driven an OB or OBXT so can't comment on the pedal feel, nor the grip of the brakes, but it does sound like the OEM bits leave the driver wanting more of both.

 

I just did this mod yesterday on my LGT using a used SJ labeled booster and a new STI BMC and my experience is identical to this. Very short distance to when pedal starts to feel stiff and maybe only another 1" of travel before it's completely solid. I haven't done any other brake upgrades, so stock calipers, regular pads, regular lines, no bracing. The pedal is night and day different now, this was a great upgrade. Thanks to the forum for providing such clear instructions!

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  • 1 year later...

Been reading this for a couple of hours now, I’ve got an ‘02 H6 outback 4EAT:

My question is will I need a similar year WRX Brake booster, (BB) or the STi BB?

 

Additionally, I gathered that Hawk HPS 5.0 pads are better than the “standard” HPS brake pads. Going stainless steel paired with the Grimmspeed master cylinder brace (confirmed to fit) match nicely.

 I’ve currently got SP performance slotted rotors F+R with semi-metallic pads just to get me to-and-fro, but I’m considering being a bit more ambitious and have considered what I can do to improve my performance and confidence with this old wagon.

I’m planning on talking to my local mechanic and I’m sure he’ll just tell me to get a new car lol.

I might not check this thread immediately, so by all means anyone is free to reach out via email:

jdukeirbyarnold@mail.com

Instagram: jamfart_2002 (preferred)

facebook: James Irby Arnold

I’m a bit new to forums to a degree so thanks for any help in advance!

- James

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  • 4 months later...
17 minutes ago, yellowspirit said:

Does anyone know the thread pitch and size specs for the brake line fittings on the Subaru master cylinder?  Asking because it may allow me not to waste so much brake fluid while bench bleeding a MC?

According to https://www.subaruoutback.org/threads/brake-line-diameter.509271/

3/16 in. is the line. 

Fittings are inverted flare M10x1.0 thread.
 

 

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2 hours ago, JamesArnold said:

According to https://www.subaruoutback.org/threads/brake-line-diameter.509271/

3/16 in. is the line. 

Fittings are inverted flare M10x1.0 thread.
 

 

 

I think it might be different for the master cylinder (versus the junction block).  I say this because I had to deal with the junction block at the rear of the Legacy GT because my brake pipes corroded and leaked.

 

But the brake pipe going from the master cylinder to ABS module looks of different diameter than the four individual brake pipes going from the ABS module to each corner of the car.

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