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Join Date: Mar 2007
Location: Rockville, MD
Posts: 793
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Brake vacuum question
I just replaced the master cylinder on a '88 Carrera and while out, tested the vacuum booster (it worked). Now back in the car, it feels like no vacuum boost under braking. Where does the booster get its vacuum from when I plug the hose into the booster.
Thanks, Chuck |
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01-16-2013, 03:04 PM
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Brake vacuum booster test.........
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Chuck, How did you test the BVB (brake vacuum booster)? With the engine idling, how much vacuum reading did you get? The vacuum hose for the BVB is connected to the engine that creates the vacuum. Keep us posted. Tony |
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01-16-2013, 03:17 PM
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Silly question, but did you make sure the square cut oring was on the master cylinder before you installed it on the booster??
Howard
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Howard Freeman 80 911 SC & 74 914 1.8 79 930 & 83 SC coupe,03 996 TT,02 996 C4 03 X/5 3.0. 370,186 miles now Sons daily driver 10 X5 3.0I 224,515 miles |
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01-16-2013, 05:40 PM
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Tony, I used an old AC vacuum tool hooked to the booster and the arm was then very easy to move. No measurments.
Howard, thanks, yes I did put in the new o-ring when I attached the MC. Maybe I better check the engine end of the vacuum hose to see if it's connected. I usually don't work on anything past 1972 and these new fangled cars puzzle me.  I asked about where vacuum comes from because my motorhome has an electric vacuum pump for the brakes.Regards, Chuck |
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01-17-2013, 08:47 AM
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Join Date: Apr 2005
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There's a hose from the booster to a metal tube on the trunk floor. Another hose connects the bottom of this tube (in the area of the pedal cluster, in the interior) to another tube that passes through the center tunnel. Aft of the tunnel, under the car, another hose connects to the tube and goes up over the torsion bar tube and eventually to the engine. This last section of hose is well known for cracking. I'd work my way through the system, as it sounds like a hose is either disconnected, or broken.
JR |
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01-17-2013, 08:57 AM
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Location: Rockville, MD
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JR - THANKS, that's exactly what I needed to know. The front hoses were good (booster and pedal area) and I'll check the rear once I get the car back on my lift.
Regards, Chuck |
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01-17-2013, 09:37 AM
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Rear brake vacuum line.......
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Chuck, You don't need to get the car on the lift to inspect the vacuum line. It is very accessible in the engine bay driver side. See picture below.  The brake vacuum line is the black hose with white plastic connector shown in the picture above. Connect a vacuum gauge to test the line or brake booster with engine at idle speed. Keep us posted. Tony |
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01-17-2013, 10:28 AM
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Join Date: Apr 2005
Location: outta here
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Tony,
The part of the hose that usually cracks is the part located under the car. There was a thread on just this subject in the past few weeks, with photos, although I can't remember who started it. Yes, there are ways to test the line without looking at it but I'm betting his will have problems. JR |
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01-17-2013, 10:38 AM
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