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BustedBus
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Joined: June 11, 2004
Posts: 52
Location: Anywhere
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 Posted: Mon Jul 02, 2012 8:14 pm Post subject: Brake booster/servo sticks brakes |
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Here's a new one for me, hopefully not for you. Did search for similar situation, to no avail.
'78, F.I.- Question for you booster/servo masters (I am not).
It's kind of like that new Infiniti JX where it hits the brakes for you to avoid rear-ending someone.  When engine is turned on, vacuum applies, and booster hits the brakes for you. Pedal down, brakes are on, bus no go. It does release after engine is off after a bit.
Does this indicate a booster failure (diaphram)? Typical booster failure just provides boost loss/vacuum leak. It seems like I'm actually getting super-boost here instead.
Any insight? Other booster part failure? Should I declare booster failure or am I missing something? MC is new and all other adjacent systems are checked and good/new (check valve, vacuum lines, etc.).
Thanks! -Chris
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Chris- BustedBus!
Specializing in used and restored parts for your 68-79 VW BayWindow Bus
877-TYPE-211 ~ www.bustedbus.com ~ [email protected] |
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germansupplyscott
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Joined: May 22, 2004
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Location: toronto
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| Posted: Mon Jul 02, 2012 8:24 pm Post subject: |
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booster has failed.
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scott lyons
http://www.germansupply.com
VW Bus-Centric Online Parts Source |
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BustedBus
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Posts: 52
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| Posted: Mon Jul 02, 2012 8:39 pm Post subject: |
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I was thinking Scott would know. Thank you sir. Isn't that a rather odd failing of it? I've never heard of/seen one do that before. What is the exact mechanism of the failure? If diaphram is shot, vacuum would pass through it and not cause it to pull the pedal. I've yet to pull one apart to learn. Now is the time.
Forgot to note that booster is totally clean. No rust/fluid inside, which usually assists in failure.
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Chris- BustedBus!
Specializing in used and restored parts for your 68-79 VW BayWindow Bus
877-TYPE-211 ~ www.bustedbus.com ~ [email protected] |
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germansupplyscott
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| Posted: Mon Jul 02, 2012 8:51 pm Post subject: |
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i don't know exactly but i had one fail that way. once the brakes are applied they do not release. disconnecting the vacuum source and seeing if the brakes release will tell you for sure.
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scott lyons
http://www.germansupply.com
VW Bus-Centric Online Parts Source |
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busdaddy
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Joined: February 12, 2004
Posts: 23879
Location: Surrey B.C. Canada, Land of the giant flying moose!
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| Posted: Mon Jul 02, 2012 9:00 pm Post subject: |
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The failure is debris under the seat of the atmosphere valve, it applies brake assist even though you haven't moved the pedal.
The cause is either a damaged or disconnected vent line to the fenderwell or a previously failed master filled it with rust promoting brake fluid.
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Rust NEVER sleeps and stock never goes out of style.
Wanted, 68-73 westy OG plaid curtains, singles OK. |
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