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Brake Booster Plumbing 

 

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 Post subject: Brake Booster Plumbing
Posted: Tue Feb 13, 2007 9:03 am 
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Hey guys,

Just wanted to check where you are running your brake booster vac line to?

I noticed in my old cars that if you were on the throttle boosting away and needed to brake suddenly then the brakes didnt work so well until the engine went into vacuum again.

Would it be better to route the vacuum hose to before the turbo? Would this provide enough vacuum?

Could this be dangerous is you blew an intercooler pipe off?
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Posted: Tue Feb 13, 2007 10:07 am 
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Vac hose before the turbo?? as in, in the intake plumbing? That's not actually going to see a vacuum condition at any stage... well, not enough vacuum for brake assist.

In the time it takes for you to come off the loud pedal, the manifold should have returned to a full state of vacuum... if it's not, then you prob need more venting from the BOV.

I was under the impression that our brake boosters have a check valve so that the booster is able to maintain a "reserve" of vaccum... so that in the event of engine stalling, you have enough brake assist to get the anchors down and keep them there.

 

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Posted: Tue Feb 13, 2007 10:16 am 
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I mean in between the filter and turbo inlet. This is always a vacuum source isnt it?

Its not a huge concern, I was just wondering if it would be better to move it. I have to redo the hose anyway because my plenum.

There were a few times in the AU where the brakes were crap as it was coming off of boost and I was in a hurry to slow down. Now I wonder if this is the reason I had trouble holding the car on the line while spooling the turbo up on the foot brake. I always had to apply the handbrake to stop creeping forward.
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Posted: Tue Feb 13, 2007 10:50 am 
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there is a check valve in the hose, it is actually the part that the hose joins to on the booster...

boosters HAVE to have enough vac storage capacity for atleast 3 self assisted brake applications... so on boost, off boost, watever, you will always have assistance

 

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Posted: Tue Feb 13, 2007 11:17 am 
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Do you think fitting this hose to before the turbo would help the brakes out when staging or is there enough assistance to stand on the brakes for more than a few seconds?

In the AU I would stand on the brakes and hard as I could and apply the handbrake for a few seconds with my foot on the throttle to build boost but it would always creep forward a little. I used to get 6psi out of it before the car would move. More boost off the line would be nice.
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Posted: Wed Feb 14, 2007 11:20 am 
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With a turbo car and no treansbrake, 6 psi off the line before it walks it a dream come true. Most guys i know struggle to get 4psi before the car walks.
How is your general pedal feel? Does the pedal feel stiff. If it does then its not a vacuum prob, its a dirty caliper/piston prob. Just means you pop the pistons out of the calipers, give the bores and pistons a good clean to get the gummy s**t off them, give em a light hone if you want, pop em together with new rubbers and they'll be heaps better.
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Posted: Wed Feb 14, 2007 11:34 am 
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That was with the AU which I dont have anymore. It only had a 2300 stall so I guess 6 psi was alright.

I think the master cylinder might have been too small for the brakes. It had AP racing 4 spots and 330mm rotors all round but the stock master cylinder. The brakes and handbrake just couldnt hold it on the line but it wouldnt wheelspin.

The EA is manual so Ill be slipping the clutch to build boost. Ill probably use a transbraked powerglide when I want to get more serious and my bank account agrees with me.
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Posted: Wed Feb 14, 2007 11:49 am 
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Have you started the car and then killed the motor and checked what the brakes feel like? There should be a reserve of vacuum and should feel the same as when the engines running...
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Posted: Wed Feb 14, 2007 11:57 am 
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No, the car doesnt run yet.

It used to feel fine. Im was just wondering if it was worthwhile plumbing that hose into the intake as I need to redo the hose anyway because I have a new plenum and the old hose doesnt reach.
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Posted: Wed Feb 14, 2007 12:30 pm 
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Im still fairly sure that the intake between air filter and turbo inlet is not a source of vacuum.

 

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Posted: Wed Feb 14, 2007 12:40 pm 
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4.9 EF Futura wrote:
Im still fairly sure that the intake between air filter and turbo inlet is not a source of vacuum.


It would have to be after the throttle body butterfly to get vacum wouldn't it?

 

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Posted: Wed Feb 14, 2007 1:07 pm 
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4.9 EF Futura wrote:
Im still fairly sure that the intake between air filter and turbo inlet is not a source of vacuum.


If you put your hand on the intake pipe it will feel suction. If you give it a rev if feels like you will lose your arm.

Its always sucking so it has to be vacuum doesnt it?
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Posted: Wed Feb 14, 2007 1:07 pm 
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Dansedgli wrote:
No, the car doesnt run yet.

It used to feel fine. Im was just wondering if it was worthwhile plumbing that hose into the intake as I need to redo the hose anyway because I have a new plenum and the old hose doesnt reach.


oh yeah

thats right ;) haha but yeah im pretty sure like what martin and others are saying - has to be engine side of the throttle to get a source of vacuum.

If you're keen you might be able to source a check valve and install that inline with the booster and see if it makes a difference?
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Posted: Wed Feb 14, 2007 1:14 pm 
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Why would vaccuum need to be after the throttle body? The engine ultimately gets it air from the intake pipe. If the T/B is closed vaccuum comes from ISC which leads to the intake pipe. If the T/B is open vaccuum comes from the air in the intake pipe anyway. Air doesnt come from anywhere else but the intake pipe.

Unless Im missing something of course :(
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Posted: Wed Feb 14, 2007 1:22 pm 
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Dansedgli wrote:
Why would vaccuum need to be after the throttle body? The engine ultimately gets it air from the intake pipe. If the T/B is closed vaccuum comes from ISC which leads to the intake pipe. If the T/B is open vaccuum comes from the air in the intake pipe anyway. Air doesnt come from anywhere else but the intake pipe.

Unless Im missing something of course :(


It's the throttle body which creates vaccum in the manifold. Engine is an air pump, drawing air. Throttle body closes and severly restricts the flow of air entering the manifold. The only air entering the manifold is coming through the ISC - a minute opening compared to the TB. Vaccum condition prevails.

When the throttle body is open on a nat/asp car, manifold pressure nears atmospheric (restriction removed between manifold and air intake), the engine is free to draw as much air as it wants. On a boosted car, it goes one step further and you get positive presure in the manifold...

 

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