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Premium Member
01/07 RSTi
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943 Posts
Discussion Starter · #1 ·
So I just swapped out my RS MC and brake booster dual stage in favor of the svx MC / single stage booster for better pedal feel, as mentioned here.

Got everything buttoned up, brakes bleed and the pedal feels nice and firm when the car is off, but the problem is there is no change in pedal feel when the car is turned on. This also makes stopping the car very difficult as you can imagine since its as though i have no power brake assit at all.

I feel like its just a bad booster and I'll have to swap it all out again. Was hoping someone here might have an idea to fix this that doesn't involve me going back to my stock booster.

btw, checked the vacuum line and its definitely sucking air, and I can't hear any leaks coming from the booster area, but it could just be covered up by the engine noise.

Thanks!
 

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Premium Member
01/07 RSTi
Joined
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943 Posts
Discussion Starter · #3 ·
I would guess the diaphragm is leaking, unless the check valve is backwards...

Someone else mentioned the check valve as a possible issue, but it looks like its internal in the boosters on both the single stage and dual stage boosters.

My vac line is just straight hose like in this pic:
 

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Premium Member
overdeveloped beater
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8,335 Posts
Check valve is definately in the hose.If there isn't a check valve, you have the wrong hose attached. It has to face the correct way or you won't build any vacuum to it.
 

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Premium Member
01/07 RSTi
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943 Posts
Discussion Starter · #6 · (Edited)
Check valve is definately in the hose.If there isn't a check valve, you have the wrong hose attached. It has to face the correct way or you won't build any vacuum to it.
The hose doesn't look like it has a valve in it. Neither does the one in the northursila photo that i posted above. I'd think that even if the hose had no valve, if the booster was working correctly the brakes would still be boosted. My understanding was that the check valve was only for keeping the brakes working for a few pumps in case of engine failure.

Air flow should be going from the booster to intake manifold if you were to blow on the hose
I disconnected the hose from the manifold to verify that it is indeed sucking air, but haven't disconnected the booster side, will try tonight.
 

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Premium Member
01/07 RSTi
Joined
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943 Posts
Discussion Starter · #7 ·
Check valve is definately in the hose.If there isn't a check valve, you have the wrong hose attached. It has to face the correct way or you won't build any vacuum to it.
OK, this was the problem. hose was on backwards. i feel smart.

just have to do some pedal adjustments now.
 

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Registered
1995 Impreza L & 1997 OBS
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2,258 Posts
lemme know how u like the feel. was just reading how it says no true performance gain, just better pedal feel. interested on doing this with the rest of my brake upgrades.
 

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Premium Member
01/07 RSTi
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943 Posts
Discussion Starter · #10 ·
lemme know how u like the feel. was just reading how it says no true performance gain, just better pedal feel. interested on doing this with the rest of my brake upgrades.
I need to mess with the pedal adjustment to tell for sure.

Gonna try doing this: http://www.rs25.com/forums/f9/t83600-everyone-has-long-pedal-travel-before-brakes-engage-read.html

Initial guess is that it doesn't feel too much better, but I'd like to do some adjustments and double check that I have all the air out of the lines.
 
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