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Discussion Starter #1
I’m gonna do a disc brake conversion on my 3rd gen. I also want to convert to power brakes. What is the minimum vacuum necessary to work the brake booster? Thanks, Matt
 

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70 Nova, 427, TKO600, Vintage Air, Terminator EFI
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I’m gonna do a disc brake conversion on my 3rd gen. I also want to convert to power brakes. What is the minimum vacuum necessary to work the brake booster? Thanks, Matt
Well, hopefully someone here can give the spec's. I don't have any but you know it becomes driving technique. If you swat the throttle the engine pulls full vacuum decelerating giving the booster at least two safe pumps. Same thing when you are stopping for a light. If you downshift while slowing for the light the engine will pull full vacuum as the vehicle decelerates so you have good brakes during this time even with an automatic. It's when you are using the brake with the engine idling and say you are parking the car applying the brake frequently. That's you're going to notice the peddle getting harder so if you have a clutch you just swat the throttle. With an automatic you may have to do a neutral throttle swat but you have to remember not to swat the throttle with an automatic in gear. Not only does the car jump but the vacuum goes away and if you panic you can be pushing down on the brake as hard as you want but if your right foot is touching the gas peddle, the car won't stop.
There are electric vacuum pumps for brake boosters and there are belt driven vacuum pumps also. A quick search on Amazon shows a unit (see the picture). I don't know the quality of this unit, it's just some info in case you have vacuum issues after your upgrade. And can't forget Hydro Boost that can be integrated into your power steering system.
 

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Discussion Starter #3
Thanks for the great info Ed. It is a 4 speed Muncie so at least I have that going for me. And I don’t have power steering or the hydra boost would be nice.
 

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Mike - 74 Nova Baltimore, MD
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I agree with Ed D.

I'm not sure what the minimum vacuum necessary to work the brake booster is... but I have about 13-14 Hg of vacuum @ idle and my power brakes (front dics/rear drums) work fine while applying the brakes several times while the engine is idling.
- What is your current vacuum level at idle?
 

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At idle? 11-12
The only reason I asked was while watching a YouTube video the guy mentioned you needed about 18 inches for the booster to work. Seemed high to me. Also, is there much difference in performance between a 9” or 11” booster?
 

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70 Nova, 427, TKO600, Vintage Air, Terminator EFI
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At idle? 11-12
The only reason I asked was while watching a YouTube video the guy mentioned you needed about 18 inches for the booster to work. Seemed high to me. Also, is there much difference in performance between a 9” or 11” booster?
Are you kidding? After driving the car with non power brakes you're gonna to have trouble keeping your face off the steering wheel when you stop. I don't think you have to worry about booster size unless you have clearance issues with a big block or something. If you have a big block I would consider the 9". That way you can do service work on the engine and not have to fight the booster to gain access.
 
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