Vacuum leak?
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Elder User
Joined: Jul 2004
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From: Fredericton NB, Canada
Vacuum leak?
Hi there. Im a new member, so I would like to say hello. I am from Fredericton NB Canada, and I have an 84 Bronco w/ a 351W HO, and a 3 speed auto. It has a nice pewter gray base coat with lots of clear. I tried to do a search for my problem, but couldnt find it. Here we go. When I am driving my truck there is what sounds to be a vacuum leak from behind the dash directly in front of me. It is not a leak in the vents, it makes this noise whether the fan is on or not.
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Elder User
Joined: Jul 2004
Posts: 757
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From: Fredericton NB, Canada
Sorry about that, I hit the wrong button and it was posted before I finished. So to continue, the strange thing is that it seems to go away a little when I depress the brake pedal, then continue when I am accelerating. The brake system is somehow tied in with this problem, but I am unable to locate any hose leaks or figure out how it would be affected by the brakes. Any help would be MUCH appreciated.
New User
Joined: Jul 2004
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I have the same problem with my '84 Bronco. I've been hearing the same noise and tried to track the leak down but could not find a leak. Yesterday, the brake light on the dash came on and pressure fades when I depress the brake pedal. I believe that the vacuum booster needs to be replaced.
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Elder User
Joined: Jul 2004
Posts: 757
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From: Fredericton NB, Canada
Vaccum booster? Thanks for the reply. It is a fairly annoying sound, and takes away from an otherwise silent cab. Is this an expensive and/or lobour intensive procedure? I have owned numerous Ford trucks, but this is the first problem I have had with a vacuum booster. Does anyone have any information on what this part is, and its function?
Thank you.
Thank you.
Senior User
Joined: Apr 2004
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I believe he is refering to the power brake booster. You should have a vacuum line running to it. It could be leaking inside of the booster somewhere. (I think).
Another thing to check, and I only say this in regards to the original problem with the noise (vacuum leak) , on my 86 EB, the speedo cable that attaches to the back of the speedometer/tach makes a noise alot like what could be construed as a vacuum leak. It changes with speed (of course). When I'm going slow it is more noticeable because the wind and motor noise is low. But as I speed up, it does get louder until the wind/motor noise drowns it out. I have sprayed it with wd-40 and it helped a little, but I think I need to just get some graphite on it and quiet it down. Just an idea. Maybe yours is a leak, but it would certainly suck to search and search for a leak where there isn't one. Just my .03
Another thing to check, and I only say this in regards to the original problem with the noise (vacuum leak) , on my 86 EB, the speedo cable that attaches to the back of the speedometer/tach makes a noise alot like what could be construed as a vacuum leak. It changes with speed (of course). When I'm going slow it is more noticeable because the wind and motor noise is low. But as I speed up, it does get louder until the wind/motor noise drowns it out. I have sprayed it with wd-40 and it helped a little, but I think I need to just get some graphite on it and quiet it down. Just an idea. Maybe yours is a leak, but it would certainly suck to search and search for a leak where there isn't one. Just my .03
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Joined: Jul 2004
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Power brake booster is what I meant. Sorry for the confusion. The booster is what provides the "power" in the power brake system. Unfortunately, if there isn't any power provided to power brakes, the brakes do not work. The part is the big drum on the firewall that the brake master cylinder is bolted to. Vacuum hose from the intake manifold is connected to a check valve on the booster. Seems to be pretty simple to replace according to my repair manual. I bought one at Auto Zone today for $114.00. I'll get $40.00 back when I return the core.
Elder User
Joined: Apr 2002
Posts: 813
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From: NJ
yes it sounds like the diaphram inside your power brake booster is leaking. usually the engine also doesnt run properly when this happens because there is a vacumn leak. troubleshoot this a little further by disconnecting the vacumn hose to the booster and plug it and see if the engine runs a little better. if so reconnect and the engine should run a little worse again.
i think to replace it you need to unbolt the master cylender and gently pull it forward without kinking the brake lines. then 4 bolts and one vacumn line and it should slide forward and out. just reverse to install.
i think to replace it you need to unbolt the master cylender and gently pull it forward without kinking the brake lines. then 4 bolts and one vacumn line and it should slide forward and out. just reverse to install.
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Elder User
Joined: Apr 2002
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From: NJ
one more thing when you replace it make sure you use the new chack valve because a backfire could ruin the new booster when pressuris forced the wrong way into the booster.
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