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Vacuum issue when applying brakes


xderbyx

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I did try searching the forum a bunch but wasn’t able to find an answer close enough to my issue here! I have a 76 with a Weber 32/36 from the PO. I live in NC so smog requirements are exempt which is a plus in my book! 
Issue I’m running into is that somewhere along the line I have a vacuum leak.. motor runs normal but when I apply the brakes, it bogs down quite a bit. I’m looking to streamline my vacuum lines a bit and hopefully find the problem along the way! Thanks guys. 
 

-Anthony

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Check the large hose that runs between the brake booster and intake manifold.  Check to make sure the hoses are tight on their connections (there are four); then start examining the hoses themselves.  Those hoses are pretty sturdy (they're wire reinforced) but to deteriorate after 40 or so years! 

 

There's a long one (booster to check valve) and a little short one (check valve to manifold.  This short one is a straight hose that's forced into a bend--for those 40+ years; it's the most logical one to crack.  Replace with the same hose from an E21 320i.  The factory learned from their mistakes and on the 320 that hose is molded with a bend in it, so isn't under constant tension.  

 

If the hoses check out, you probably have a leak in the booster itself.  There are places that can rebuild your booster with a new diaphragm, but those boosters are pretty long-lived.

 

mike

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42 minutes ago, FunElan said:

There is a vacuum line coming from the booster with a check valve. May be the place to start. 

 

PS, welcome to the faq!

 

39 minutes ago, mike said:

Check the large hose that runs between the brake booster and intake manifold.  Check to make sure the hoses are tight on their connections (there are four); then start examining the hoses themselves.  Those hoses are pretty sturdy (they're wire reinforced) but to deteriorate after 40 or so years! 

 

There's a long one (booster to check valve) and a little short one (check valve to manifold.  This short one is a straight hose that's forced into a bend--for those 40+ years; it's the most logical one to crack.  Replace with the same hose from an E21 320i.  The factory learned from their mistakes and on the 320 that hose is molded with a bend in it, so isn't under constant tension.  

 

If the hoses check out, you probably have a leak in the booster itself.  There are places that can rebuild your booster with a new diaphragm, but those boosters are pretty long-lived.

 

mike

Thanks for the replies! I did actually replace the long hose and check valve but didn’t replace the bent one yet. I didn’t see any visible damage to it but who knows if there’s something tiny, I’ll replace that when I can get the e21 320i hose (thanks for that tip mike!). 
my only thought is that if the booster itself wasn’t holding tight, wouldn’t I have real stiff brakes? After a ton of bleeding I got them to be working well and (hopefully) ruled out the booster as a defect!

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I had a similar issue. When I pressed the brake the engine would have a vacuum leak and cause it to shake a bunch.  The shaking got worse over time, and the problem did end up being the booster, it needed to be rebuilt. 
 

from my understanding, the diaphragm starts to deteriorate if you get brake fluid in the booster, which is what happened to my car. 
 

got the booster rebuilt and solved the problem 

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12 hours ago, Cooper said:

I had a similar issue. When I pressed the brake the engine would have a vacuum leak and cause it to shake a bunch.  The shaking got worse over time, and the problem did end up being the booster, it needed to be rebuilt. 
 

from my understanding, the diaphragm starts to deteriorate if you get brake fluid in the booster, which is what happened to my car. 
 

got the booster rebuilt and solved the problem 

This is both good, and bad news hah. Was hoping I dodged that bullet. Thanks!

 

12 hours ago, Mark92131 said:

 

That long hose needs to be special wire reinforced brake hose as Mike pointed out, not just heater hose, part No. 34331108710 or

34331115926

for the BMW 320i

Otherwise, it will collapse under vacuum.

 

Mark92131

Awesome, thanks mark

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