Hissing sound inside cab
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Posting Guru
Joined: Dec 2012
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From: abilene kansas
Hissing sound inside cab
I have been hearing a hissing sound inside the cab of My truck as I'm driving. When I shut the engine off I will still hear the sound for about 10 sec and it will stop. I raised the hood with it running, and I did not hear any vacuum leaks under the hood. What should I be checking next? 
Post Fiend
Joined: Dec 2007
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From: Lost
The part about the hissing lasting ~10 seconds after shutdown, leads me to suspect booster more. However, if the truck has factory A/C, you do have a valid point.
Dealer installed A/C doesn't use vacuum, though, so I tend to forget about that aspect since mine has the dealer installed system.....
Dealer installed A/C doesn't use vacuum, though, so I tend to forget about that aspect since mine has the dealer installed system.....
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Joined: Jan 2001
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From: Virginia
If you want to make sure it's the booster, disconnect it and plug the vacuum line, and then see if the hissing goes away. Don't drive it with the hose off the booster though, the brakes won't be very good.
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Posting Guru
Joined: Dec 2012
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From: abilene kansas
Crap, not the kind of news I needed. I wonder if the check valve that the booster hose goes on could be bad? The power brakes work perfectly despite the hissing.I will pull the hose and plug it to see what happens. Since I do not have the funds to replace it, I may have to live with it.
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From: abilene kansas
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Post Fiend
Joined: Jul 2004
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From: Northern California
Hmmm, both brake booster, and HVAC controls leaking?
Does the truck have Factory A/C? Or did it at one time?
Any aftermarket vacuum gauges installed etc?
Does the truck have Factory A/C? Or did it at one time?
Any aftermarket vacuum gauges installed etc?
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Thread Starter
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Posting Guru
Joined: Dec 2012
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From: abilene kansas
Put My ear to the firewall, definately the booster.
So for now I will have to live with it till I can afford to fix it,unless someone has one they will give Me
Post Fiend
Joined: Jul 2004
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From: Northern California
I was just wondering why if you plugged the booster vacuum line that it would still make noise...
If it's the booster, best to get it fixed as soon as possible.
good luck.
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Posting Guru
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From: abilene kansas
I'll just have to be careful with it, as I do not have any more cash to spend right now
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Joined: Nov 2007
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From: Denver Metro Area, CO
If you disconnect and plug the vacuum line to the booster, that removes the booster and check valve from the system, I also wonder how the booster could still be making noise if you did this?
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Posting Guru
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From: abilene kansas
I have no clue, ,this problem is not really affecting the power brakes, they are working as normal