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Old 06-15-2020, 02:18 AM   #1
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Mystery brake system

I have a 1981 gmc b6000 with a dual power brake system. It has a vacuum booster attached to what I guess is called a "power head" which is supplied with fluid from the power steering pump. the power head then attaches to the master cylinder. After hours of searching the web I have come to the conclusion that I must be the only bus with such a system. Power steering fluid is dumping/bubbling from the weep hole in-between the master cylinder and the booster. I cannot find a single bit of info on this system. Any help would be much appreciated
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Old 06-15-2020, 05:07 AM   #2
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What you have is a hydraboost system for your power brakes getting boost from the power steering pump. On older buses it would have been a vacuum booster working over intake vacuum.



The hydraboost system is pretty much identical to the hydraboost systems used in C/K2500 and larger trucks, vans, and SUV's. The only difference on your bus is your hydraboost system also has an electric override system that will power up the booster if the engine should quit or the power steering pump should fail.



It sounds as if the seals in the power booster have failed. Swapping out a power brake booster is not all that different from swapping out a power brake booster in a pickup. It is just bigger and has a few more connections.


Brake Systems, Inc. in Portland, OR is one of the best places to get replacement boosters or your own booster rebuilt. https://www.brakesystemsinc.com/products.html


Potter Webster in Portland and Longview also have a good line of brake parts for medium duty to heavy duty vehicles. </title> <script src="/_theme/jquery.js" type="text/javascript"></script> <link href="/_theme/templates/potterwebster/favicon.ico" rel="shortcut icon" type="/_theme/image/vnd.microsoft.icon" /> <link rel="stylesheet" href="/_theme/plugins/system/qlue


A photo of your actual booster would be helpful.


Good luck.
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Old 06-15-2020, 05:14 AM   #3
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The electric override booster will work with the key off and the engine not running. You should be able to hear the booster engaging when you step on the brake pedal with the engine not running and the key in the off position.


If you don't hear the override booster engaging you have other problems in your brake booster.


If you can, take a few clear photos of your booster in the bus so we can see what it is you are talking about.



You know what they say, a picture is worth a thousand words.
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Old 06-15-2020, 05:17 AM   #4
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It is not the hydroboost system I promise;) it is called a dual boost GMC Brake Parts for Buses and Trucks go to that link and go down to brake boosters. My system is the type 3
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Old 06-15-2020, 05:24 AM   #5
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The picture in my post is the exact system I have. There is absolutely no info on the web about it. That is probably why no one knows what I am talking about. If you click on that image it should unfuzz it. My system is the type3 it uses both a vacuum and hydrolic booster here is the link to that photo GMC Brake Parts for Buses and Trucks
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Old 06-15-2020, 05:29 AM   #6
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I will take pictures in the morning and post them up for you. I really appreciate all the info though. It would be awesome if I could just swap it for the hydroboost system and ditch the vacuum booster.
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Old 06-15-2020, 05:39 AM   #7
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That image is the only one that I have found and it's an illustration! I took the entire system apart in hopes that I could rebuild the hydro booster but unlike the hydro booster mine is one piece with the internals staked in to the housing of the booster. So without gouging the hell out of it I cannot access the seals to possibly replace them
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Old 06-15-2020, 05:50 AM   #8
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Supposedly this system was used on Chevy and gmc from 1971-1991. My theory is anyone who has had to deal with finding info or parts for this system probably doesn't want to talk about it because of what a pain in the ass it is to find either.
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