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Old 08-11-2012, 08:31 PM
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Vacuum for Power Brakes!

I am needing some suggestions on sorting out my power brakes!
Most of the stuff is from Speedway, 4 wheel GM Metric disc brakes, rears have
mechanical parking brake. Single diaphram booster with Corvette style master
cylinder.
The engine is a small block Chevy 383 stroker with a vintage Babe Erson cam
that I have some info on. The duration, 218 degrees @ .050, 104 degree lobe separation, lift .456 Int, .449 Exh.
Pretty lumpy @ Idle.
Intake manifold is Edelbrock Performer EPS with Edelbrock 650 cfm #1406.
I wonder about where to pull the vacuum for the brake booster?
Right now the vacuum is coming from the top right side of the intake manifold.
I know that the carb has a large vacuum port in the back-middle above the base
which is now plugged.
What about vacuum pumps or canisters?
The brakes willl stop the truck but just not good enough to lock them up or stop fast!
Help me out!
Thanks! Joe
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Old 08-11-2012, 10:44 PM
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Hi Joe,

104 LS sounds pretty hairy even with the 218 .050 duration. I run a 106 with 230, and after years of trying I have it idling smoothly at 1000rpm! No problem with a 3000-stall converter. It will go lower, but I hate lumpy idle. Bad for the valve train IMO.

I run my vacuum line from the tail of the Holley to a Summit booster can (visible as the yellow thing in the photo), then from that to the normal canister. Effectively just makes a bigger canister. It works fine for me; I've locked the brakes once trying to skid around an idiot who stopped short on the highway near a ramp (successfully, I might add). Without it I had a hard time stopping at a red light; very unnerving! If you need to, you can daisy chain as many of them as you can stand to get enough volume. I think one will do it though.

You can run the vacuum hose either from the carb base or the intake manifold; same difference. Carb base is easier since no further plumbing is required, but your setup ought to work ok too.

You shouldn't need a vacuum pump. The only street cars I've seen with them were improperly plumbed (like a 'Vette I saw with a 6-71 that ought to never see less than about 12" of vacuum at the carb base).

Last edited by Leoman; 08-11-2012 at 11:09 PM. Reason: mention picture
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Old 08-15-2012, 10:31 AM
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Have you put a vacuum gauge on the engine to determine what the vacuum reading is? I tried a tank in addition to my booster to increase the volume, but it still didn't give me enough stopping power. I eventually removed the booster and run mine as a manual master, and it stops better than it did with a low vacuum system and booster.
I can't imagine that a 4wheel disc system wont put a light car on it's nose if you had enough vacuum. You could add a vacuum pump to work it, but they're spendy and noisy. I borrowed one from a friend to try, but it was noisier than my electric fuel pump!
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Old 08-15-2012, 08:15 PM
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I'll get back to you!

I thank all of you for your ideas! The truck is presently at a friend's house having an
oak roof structure built for it. As soon as I get it back I will get after it with a vacuum gauge, relocate my vacuum takeoff at the carb base and go from there.
I will keep you posted as I sort this out and let you know what I find!
Thanks! Joe
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Old 10-27-2012, 06:20 PM
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Gettin' there!

I' ve been going over my brake system and this is what I have now:
The biggest problem I had was not enough throw from the pedal pivot to the master cylinder rod. I extended the throw but lost some leverage up top! But before I was not moving the MC piston enough. Now If I nail the brakes it will lockup and slide, a vast improvement!
I have found that my engine makes 9" of vac at idle, bring it up to 1200 rpm, it will produce 20". So now I have to decide how I want to go about producing vacuum when I'm in traffic and can't produce the RPMs' to bring up the vacuum.
At least now I know I can stop but sometimes it just takes more pedal pressure!
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