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10-17-2010, 12:08 AM | #1 |
Registered User
Join Date: Feb 2009
Location: franklin kentucky
Posts: 70
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hissing when hitting the brake pedal
my truck is making a hissing noise when i hit the brake pedal the idle raises which clearly is a vaccum leak. well i was told it was the vaccum booster, well i replaced it today and it didn't take care of the hissing when i hit the brakes. i don't know what it is so a buddy and i are going to tear into the dash. it sounds like it's coming from behind the ac controls above the radio but i'm not sure. i can't hear any kind of hissing under the hood but i also have headers to cherry bombs to 3 1/2" tips in front of the rear tires so it's kinda hard to hear anything. any ideas where the leak could be coming from would be greatly appreciated.
Last edited by jklonowski; 10-17-2010 at 12:09 AM. |
10-17-2010, 08:04 PM | #2 |
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Join Date: Oct 2008
Location: Marianna Arkansas
Posts: 7,277
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Re: hissing when hitting the brake pedal
The flapper doors that control the movement of the heat and air system are vaccum controlled. The movements of the flow are also[ from top of the dash to center to floor]. Your vac leak is probablly right where you thought it was above the radio. Jim
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10-17-2010, 11:07 PM | #3 |
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Join Date: Sep 2010
Location: The Dalles, OR
Posts: 392
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Re: hissing when hitting the brake pedal
I had a jeep that was the same way. It was a vac actuator behind the dash for the heat/def/ac selector.
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10-17-2010, 11:16 PM | #4 |
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Join Date: May 2004
Location: Caldwell,Tx.
Posts: 3,648
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Re: hissing when hitting the brake pedal
Was the new booster used or new? If it is used then it is also bad. The only thing that would cause a hiss when you press the pedal would seem to be a bad booster. If you want to be sure , disconnect the vacuum from the booster and cycle the pedal a couple times and see if the noise is gone.
Frank
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10-18-2010, 09:46 AM | #5 |
78K & 79C Jimmys
Join Date: Nov 2009
Location: Ottawa Ont CANADA
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Re: hissing when hitting the brake pedal
if not the booster,look here
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John 1978 GMCJimmy4X4-350/203 1979 GMCJimmy4X2-305/350 Last edited by motornut; 10-18-2010 at 09:47 AM. |
10-18-2010, 10:25 AM | #6 |
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Join Date: Sep 2005
Location: Sun City West, Az
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Re: hissing when hitting the brake pedal
iv'e had that happen on a couple of rigs in the past and both times like frank said,it was the booster.but.since you replaced it.it seems kinda odd it would be bad.
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10-18-2010, 07:22 PM | #7 |
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Join Date: Feb 2009
Location: franklin kentucky
Posts: 70
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Re: hissing when hitting the brake pedal
solved it after i changed the booster and went ahead and changed the master cylinder as well. it was a vacuum plunger like switch that was connected to the brake pedal. i guess it was used to kill the cruise when the brakes we engaged. it used a vacuum line that was "T" from the brake booster line and went through the firewall down where that ball is next to the brake booster. sucks i wasted over a hundred dollars just to disconnect a vacuum line. awe well at least i don't have to worry bout them for awhile i hope lol
Last edited by jklonowski; 10-18-2010 at 07:24 PM. |
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