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Old 06-21-2008, 10:00 PM   #1
djs69stang
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Default brake booster vacuum line to?

I have installed the new Edelbrock 600 cfm barb, it idles and runs great! But when the brakes are applied, yuck, the engine runs somewhat rough and the brakes are minimal with me having to push the pedal hard. There were no problems with the brakes before the install and the booster is running off the manifold. There is a port on the back of the EDL carb, should I run the booster on that port? Nothing in the manual says to do or not to do, it just says some guys do so, if not then it should be plugged which it is.
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Old 06-22-2008, 12:01 AM   #2
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Sounds like a vacuum leak somewhere. your brakes should be hooked to the intake , the port in the rear would work as well but it's all the same thing. what about your idle mixture ?

Could be a leak but not bad enough to detect until the added draw of the booster comes on. cover the air horn slowly with a rag with it at an idle, if it speeds up you have a leak.
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Old 06-22-2008, 01:04 AM   #3
jerry69
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Your hose from the booster goes to the rear port of the Edelbrock . Here's FAQ from Edelbrocks web site.
Q: Can I run my PCV line to the rear of the carburetor?
A: We do not recommend routing the PCV line to the rear of the carburetor. We recommend that the PCV line go to the front, if you have power brakes, they go to the rear.

Hope this helps, I'm running the same with my 69 Mustang and 71 Chevelle....
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Old 06-22-2008, 04:28 PM   #4
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Default Manual brakes instead of power, why

Quote:
Originally Posted by jerry69 View Post
Your hose from the booster goes to the rear port of the Edelbrock . Here's FAQ from Edelbrocks web site.
Q: Can I run my PCV line to the rear of the carburetor?
A: We do not recommend routing the PCV line to the rear of the carburetor. We recommend that the PCV line go to the front, if you have power brakes, they go to the rear.

Hope this helps, I'm running the same with my 69 Mustang and 71 Chevelle....

I put the brake booster on the rear of the carb, blocked off the previous intake port, and when I step on the brake pedal, the rpm's surge 500, and the brakes are still manual instead of power. But, I will say this, whereas before the engine would run rough upon pushing the brake pedal, now it stays smooth.
When I popped off the inlet on the brake booster there was a surge of air which should mean that it is holding vacuum right?
The fluid level in the master cylinder is fine.
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Old 06-22-2008, 05:03 PM   #5
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OK I'm wondering if you have a leak at idle... try this. start the car and check your RPM's without stepping on the brakes, shut the car off..... Now take that power booster hose off the back of the carburator and plug it and restart the engine...should be the same RPM's at idle..... If you have an increase with it plugged off then your booster is leaking on one side..... When you step on the brakes with the hose hooked up then it's blocking off where the vacuum leak is.... On both my cars with the same set up there is no RPM change.....

Last edited by jerry69; 06-22-2008 at 05:22 PM..
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Old 06-23-2008, 09:24 PM   #6
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I started the car with the current set up of brake booster vacuum to rear of EDL carb, warm up, idle is at 800. I disconnected the brk bstr line and plugged the back of the carb, idle is at 800. I connected the brk bstr line to the intake manifold tree on the rear, idle is at 1000, and when I touch the brake the rpm surges a few hundred, and the engine runs rough. Engine runs smooth when the brk bstr is connected to the carb and surge in rpms is greater. No matter what the brk bstr line connected to, no power brakes.
I think I will rip everything off the IM, take the IM off and reseal it.
I also think that my brk bstr may be shot.
Stupid engine is going to be the death of me this year!!!!!!!!!!!
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Old 06-23-2008, 09:40 PM   #7
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Check the, I don't know what you call it, plug at the booster. My Cougar was acting up, and I found that this gasket dang thing was cracked. Replaced it, problem went away. Just check it.
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Old 06-23-2008, 10:26 PM   #8
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I found this on brake boosters and looks like either a check valve or diaphragm could be your problem...

Vacuum enters the booster through a check valve on the booster. The check valve is connected to the engine with a rubber hose and acts as a one-way valve that allows vacuum to enter the booster but does not let it escape. The booster is an empty shell that is divided into two chambers by a rubber diaphragm. There is a valve in the diaphragm that remains open while your foot is off the brake pedal so that vacuum is allowed to fill both chambers. When you step on the brake pedal, the valve in the diaphragm closes, separating the two chambers and another valve opens to allow air in the chamber on the brake pedal side. This is what provides the power assist.
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Old 06-25-2008, 10:04 PM   #9
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Quote:
Originally Posted by jerry69 View Post
I found this on brake boosters and looks like either a check valve or diaphragm could be your problem...

Vacuum enters the booster through a check valve on the booster. The check valve is connected to the engine with a rubber hose and acts as a one-way valve that allows vacuum to enter the booster but does not let it escape. The booster is an empty shell that is divided into two chambers by a rubber diaphragm. There is a valve in the diaphragm that remains open while your foot is off the brake pedal so that vacuum is allowed to fill both chambers. When you step on the brake pedal, the valve in the diaphragm closes, separating the two chambers and another valve opens to allow air in the chamber on the brake pedal side. This is what provides the power assist.
Is this something I can rebuild, I have not had one apart but it sounds like there is not too much to the item. Probably a weekend thing for now anyway.
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Old 06-26-2008, 12:49 AM   #10
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Myself I never had and since stopping might save your life I would just buy another booster..... Check out www.rockauto.com you might get a good deal there. I just bought rear drums for $26.00 each and the big 3 Autozone, Napa and Checker wanted $72.00 each.... I ended up getting 2 drums, 2 wheel cylinders and new brake shoes...all A C Delco with shipping for $110.00 so I saved a bundle.... good luck.
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