What are the symptoms of a leaking brake booster vacuum? - 6SpeedOnline - Porsche Forum and Luxury Car Resource



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What are the symptoms of a leaking brake booster vacuum?

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Old 06-18-2012, 07:01 AM
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What are the symptoms of a leaking brake booster vacuum?

hi all, I am trying to work out why my brake pedal feel isnt as i think it should be. I have changed Pads to EBC yellow, new brake fluid and have run them in for 1000kms... it still doesnt feel stiff and beefy enough... the travel is too much and the grip doesnt feel right. The car stops but the feel is wrong is you get what i am trying to say.Both my and my wife''s C-Class feels a lot better. I was wondering what the impact of a tiny leak on a brake vacuum pipe would be? what would that do to pedal feel??
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Old 06-18-2012, 09:58 AM
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one more thing...the reason that i ask is that this problem has been troubling me for a while...hence the change of the pads and b/fluid... today however i was messing about on my way to work and accelerated and saw the boost hit max just before i got off the gas and pressed the brake -which felt much firmer and grippier...hence my question about vacuum... If the car is at high rpm or high load, the vacuum (which i assume is from the intake as with other cars) is much higher and the brake servo is thus better "assisted"

does this make any sense to the more technical among you?
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Old 06-18-2012, 04:11 PM
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It sounds like two questions... The travel should be restored when you pump the brakes. Pumping the brakes causes the lines to be filled to capacity and, provided you have enough fluid in the reservoir, the next time you press the pedal you should feel immediate results.

The "feel" would be affected more by the brake fluid integrity and any assist provided by the braking system.

I would expect that air in the lines would cause both of your issues. Are you absolutely certain whoever changed your brake fluid didn't screw the pooch on the job?
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Old 07-21-2012, 05:27 PM
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930 brake booster vacuum?

My question to someone out there is how does a 930 produce manifold VACUUM. The turbocharger, by definition, produces a POSITIVE manifold PRESSURE, not a NEGATIVE VACUUM. This is verified by the boost gauge - mine never goes below zero (0), and on full boost goes up to 1.0. Normally aspirated cars would show a vacuum (negative pressure) which is what ordinarily works the vacuum brake booster. So where does the vacuum come from in a turbocharged engine??
My modified '79 930 currently has a very hard brake pedal - similar to a n/a car with a bad booster, or when the engine is shut off and vacuum is no longer available.
Any ideas??
RevRon
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Old 07-22-2012, 06:43 AM
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When I first upgraded my brake system I had long pedal travel. Had my tech rebleed the system and that got all the air out and then the pedal feel was as it should be. I think this may be your problem.
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Old 07-22-2012, 07:01 AM
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I had same issue when i used the EBC,then i reinstalled the oem and now its perfect.
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Old 07-22-2012, 12:08 PM
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I wonder if thats what I have going on too? Pedal feels hard and never really has the BITE brakes should. Our Honda Van has more feel.
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Old 07-23-2012, 04:30 PM
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ThankS for the input guys. I think it's time to bite the bullet and re bleed the brakes. Wish me luck!!
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Old 12-28-2012, 09:09 PM
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Did you find the problem? I am with a similar problem anyone have the diagram for the brake vacuum on the 996tt to see where we have to look at please?
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Old 12-28-2012, 09:30 PM
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Originally Posted by contigo View Post
Did you find the problem? I am with a similar problem anyone have the diagram for the brake vacuum on the 996tt to see where we have to look at please?

If you suspect a vacuum leak and your brakes a bleed properly may be you can start looking at the vacuum line pickup on the engine. On the left side close to the diverter valves you got the line and it is held with a snap ring and two couplings....
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Last edited by jpflip; 12-28-2012 at 09:45 PM.
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Old 12-29-2012, 09:45 AM
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Quote:
Originally Posted by jpflip View Post
If you suspect a vacuum leak and your brakes a bleed properly may be you can start looking at the vacuum line pickup on the engine. On the left side close to the diverter valves you got the line and it is held with a snap ring and two couplings....
Advise to anybody messing with this line. If you loose or break any part of this line you will be waiting for the whole line that goes from the front to the rear of the car to come from germany. Nobody hear stocks it. Ask me how I know

The fitting has a plastic C-clip that locks the fitting from sliding to the unlocked position. The fitting is similar to those plastic home plastic line press in fittings.
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Old 12-29-2012, 09:50 AM
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Originally Posted by VAGscum View Post
Advise to anybody messing with this line. If you loose or break any part of this line you will be waiting for the whole line that goes from the front to the rear of the car to come from germany. Nobody hear stocks it. Ask me how I know

The fitting has a plastic C-clip that locks the fitting from sliding to the unlocked position. The fitting is similar to those plastic home plastic line press in fittings.
Ouch! Did you forgot to disconnect it when you remove the engine? May be I should not ask this question
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Old 12-29-2012, 10:02 AM
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Quote:
Originally Posted by dynamic gt2 View Post
I had same issue when i used the EBC,then i reinstalled the oem and now its perfect.
The EBC pads would effect brake grip, but not the pedal travel assuming same depth pads(such as worn out pads versus new). It sounds like he has air in his lines.

To the OP,

Did you use a power bleeder to bleed or did you have somebody just pump the brakes? The older cars pre modern ABS systems could be bled with just somebody pumping the pedal, but the newer systems require a power type bleeder. And when you bleed pump the brake pedals a bunch in numerous intervals between switching between brake bleeders on each caliper. And when bleeding use a rubber mallet to hit the calipers and vibrate any small bubbles out. Trust me, this will help. Also, I would always avoid draining a resevoir to empty. Always top off and bleed until you get clean fluid. I don't mean to insult your intelligence on the subject as I am unaware of your skill or knowledge on the matter. Just want to make sure you have all the info to help you.
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Old 12-29-2012, 10:07 AM
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I also trigger the abs (booster) pump with PST2 as mention in the repair manual (page 830) but was told by Loren on Renntech it is necessary only if you completely empty the system which was my case... (note: this function is now available with Durametric 6)

Last edited by jpflip; 12-29-2012 at 10:10 AM.
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Old 12-29-2012, 10:12 AM
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Quote:
Originally Posted by jpflip View Post
I also trigger the abs (booster) pump with PST2 as mention in the repair manual (page 830) but was told by Loren on Renntech it is necessary only if you completely empty the system which was my case...
Great advise. When you completely empty it is tough to bleed. That is why I avoid emptying the systems on newer cars. I have heard that bubbles in the ABS portion can also we worked out by bleeding driving and bleeding in a few cycles.
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