Power booster hissing

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Sep 23, 2004 | 02:28 AM

73f350sc

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From: Murray

Power booster hissing

Hey guys,
I'm a little worried about my brakes right now. I have this hissing sound coming from between my power booster and master cylinder. Is this something I should be worried about. I know it isnt normal, I have a 73 F350 Super Camper if that helps any with recomendations.
Thanks in advance,
-Chris

Sep 23, 2004 | 09:46 AM

hdgapeach

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From: Franklin, GA

Most likely a vacuum leak. Before you go replacing parts, confirm that it is actually the booster that is leaking. Check the hose that connects to the booster in the area around the fitting on the booster and make sure the hose doesn't have a split or tear. Lot quicker, easier, and cheaper if you're fortunate enough for it to be the hose and not the booster's diaphram.

Sep 23, 2004 | 07:24 PM

73f350sc

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From: Murray

Well if I put my finger underneath between the master cylinder and booseter I can feel it and if I cover that area it stops hissing.
-Chris

Sep 24, 2004 | 12:07 AM

hdgapeach

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From: Franklin, GA

It's the booster's diaphragm then. Hardest part of replacing it is immitating a contortionist while you're under the dash removing nuts and disconnecting the rod from the brake pedal. You can remove the master cylinder without removing the lines. Just don't kink the steel lines when you move it forward enough to remove the booster. Check for brake fluid in the front of the booster too. If there is some in there, it came from the leaking master cylinder and that's what caused your vacuum leak in the first place. If the master cylinder is leaking, replace it with a rebuilt unit when you get the new booster. And don't forget to bench bleed the master cylinder before you install it on the truck. Another hint that may or may not apply to your situation is if you are loosing brake fluid and have white exhaust smoke, the booster vacuum line is sucking brake fluid into the intake. This indicates a master cylinder leaking from the rear. Sounds like a good way to kill a Saturday morning!

Sep 24, 2004 | 01:28 AM

73f350sc

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From: Murray

Well I havent been losing any brake fluid yet but thats what I thought it might be. Do you know where I can get a new booster? And could you explain to me or PM me some more details on the process of replacing it. Kinda new to this whole brake thing. I wanna start working on my own after some bad experiences in the past.
Thanks in advance and thanks for all the info,
-Chris

Sep 24, 2004 | 01:41 AM

hdgapeach

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From: Franklin, GA

Most any chain store part house should have or be able to get you what parts you need. It's not too bad of a job to do either. If you have the part on hand, you should be able to do it in a morning's time. Remove the nuts that holds the master cylinder to the booster and pull it foward being careful not to compromise the metal brake lines. Remove the booster's vacuum hose. Move to the interior with a light so you can see under the dash and proceed to remove the nuts from the firewall that retain the booster in it's place and disconnect the booster's connecting rod from the brake pedal lever. Sounds a little easier than it is cause it's cramped and uncomfortable under there. Back under the hood, remove the booster from the firewall. Installation is a reversal of the removal. Be sure to maintain a good gasket seal at the firewall to the booster during installation. Don't want to have cold winter air blowing up your pant leg!