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Veteran
Posts: 255
 
Location: Acton, MA | If the engine is turned off, and I step on the brakes, it is normal to hear some hissing right? That is just some air moving into the vacuum tank when the brake booster bellows moves right (left over vacuum pressure in the booster tank)? In other words, it is not an indication of a vacuum leak right? My power brakes seem to work fine but I am trying to track down an engine hesitation (see comments in engine forum thread by from me).
Rebecca |
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Board Moderator
Posts: 3186
 
Location: The not-so-great, dirty-white North ( Michigan) | THat is normal when you press the brake, as the vacuum in the tank is being bled into the booster. |
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Veteran
Posts: 255
Location: Acton, MA | Thanks. That is what I expected but since I am looking for vacuum leaks I wanted to make sure. I am going to disconnect the hose from the booster tank and connect it to a vacuum gauge. This means that any vacuum leak in the brake system would not be measured by the gauge. My brakes work though so it is probably fine.
Rebecca |
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Expert
Posts: 2824
Location: Snohomish, WA. | Rebecca,
Have you ever put a vacuum gauge on that beast? What does it show at idle? A hesitation can be a low vacuum situation, or an improper accelerator pump rate (either too much or too little) due to the wrong hole being used on the carb linkage.
It can also be bad or poorly routed wires that are arcing to ground (instead of at the plug electrodes) or even a dirty distributor cap.
But the place to start is a vacuum gauge.
Mike |
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Veteran
Posts: 255
Location: Acton, MA | I tried to buy a vacuum gauge today but two stores that I went to were out of them. I suspect I will find one tomorrow. I did notice that I am going to need a way to adapt it to the size of the 1/2 hose that is on my intake manifold.
Rebecca |
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Member
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Location: Central Florida | I sometimes hear hissing when I hit the brakes while driving, and then the engine does idle rougher. This certainly is a vacuum leak at the booster. If [when] it gets worse I'll deal with it. Tip - once I remove the booster/master cylinder assembly, I cut the bracket into 2 pieces so in the future I can remove the booster without having to remove the mc. |
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Veteran
Posts: 255
Location: Acton, MA | Last night I measured the vacuum pressure. At idle it was a steady 20 inches. the needle was vibrating a little. This went away if I advanced the throttle a little. I am sure that this is because of a little leaking past the rings. I already knew about that.
Rebecca |
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normal to hear a little hissing right?
