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Old 01-30-2009, 08:17 PM
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Are all brake boosters the same?

What's the deal with the under floor, 50's stock location, power brake units? Do they measure up? If I slam on the brakes, will I get the same performance as the larger, firewall mounted booster?

TIA

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Old 01-31-2009, 09:04 AM
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The short answer to your question is yes, they do measure up and do give good performance.

As you might have guessed, lots of guys want power brakes on their rods but don't like the look of that power booster slug dangling over their beautiful engine. Also, if you are running a hood off roadster, rat rod, etc., no self respecting rodder wants that ugly thing anywhere in sight. Most logical solution is put it under the car. As you also surmise, with power brake boosters, bigger is definitely better. The larger the diameter of the unit, the more diaphragm exposed to vacuum => the more power applied to brakes (psi X sqin = lbs of force). Further, the booster must be smaller diameter, yielding an anemic power brake right? Well, enter the Detroit innovation of the dual diaphragm booster design. These have two isolated vacuum chambers and two diaphragms acting on the brake rod. Thus a single 7" booster has about 35sqin of diaphragm area but a dual diaphragm has over 70sqin of area which is about equal to a robust 10" dia unit. Thus you have you cake and eat it too; big vacuum boost and small size. Obviously the small diameter units also work great on the dash when you need the small size to fit around the 671 blowered 392 hemi in your Gremlin.
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Old 01-31-2009, 01:57 PM
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Gonna have to get me one of those dual diaphram 7" boosters for the Elky.
Absolutely no room for a larger one---and I would like a bit more help stopping dept. My current 7" just don't quite get it done.
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Old 01-31-2009, 02:08 PM
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Me too! The '59 Elky my grandson and I are working on needs a complete master cylinders so plan on getting on from Pick-A-Part. Here is an article on installing a late model 7" dual on a 60s muscle car. Bracket will be the only mini-problem but the fix in the article might work on the older car too. Worst case is I will need to build my own. Doing it this way for several reasons. First can't see spending a couple hundred $$ on a part that I can get from the junk yard for a few bucks, and second, I want the grandson to learn how everything works and rebuilding them is the #1 way to do that. Attacking a SBC and a junk yard 200R4 this summer!!
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Old 01-31-2009, 03:20 PM
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I've ben thinking about this and am wondering if you all know if it would work or not. Would it work to mount the Master Cylinder on the firewall and mount the booster on the back of the firewall under the dash? That way I could have power brakes,without the booster hanging out theere in view.

Shane
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Old 01-31-2009, 10:46 PM
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Sure. I have seen many rods that have sunken boosters either in a recess in the firewall or hidden behind it. Just have to work out the logistics of how to do it but it can be done. Need a fairly large under-dash area to pull it off like on a 60s and up mid to full size car or most any pickup.
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Old 02-01-2009, 03:27 AM
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And then of course you have the reverse mount 90 degree underdash version, too.
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Old 02-01-2009, 07:05 AM
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Thanks!!

I appreciate all the good suggestions. My Conestoga has minimal room even under the floor, but my pickup has acres.

Are these late model 7" dual MC's available in a junkyard? What cars came with them from the factory?

Thanks again,

Jeff
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Old 02-01-2009, 09:14 PM
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There are junk yard units. See the link I posted several posts above for the cars to look for. Mid 80s GM G bodies in particular.
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Old 02-02-2009, 08:08 AM
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Thanks again!
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Old 02-02-2009, 10:23 AM
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Here is some info I found on a vendor site;

"The 7" street rod booster requires 18" of vacuum to operate properly. With this vacuum level the booster will produce a maximum pressure output of 950 psi with a 1" bore master cylinder. This pressure level will work great for four wheel drum systems and disc/drum vehicles which are relatively light. This booster is not recommended for heavy disc brake cars like 55 Chevy's or for any four wheel disc brake system."

"The 7" dual diaphragm street rod booster requires 18" of vacuum to operate properly. With this vacuum level the booster will produce a maximum pressure output of about 1200 psi with a 1" bore master cylinder. This pressure level will work great for four wheel disc systems and disc/drum vehicles which are heavier."

"The 8" booster requires 18" of vacuum to operate properly. With this vacuum level the booster will produce a maximum pressure output of 1200 psi with a 1" bore master cylinder. This pressure level will work great for four wheel disc systems and disc/drum vehicles which are heavier. This booster is recommended for heavy disc brake cars like 55 Chevy's or for any four wheel disc brake system."

"The 9" dual diaphragm ultra booster requires 18" of vacuum to operate properly. With this vacuum level the booster will produce a maximum pressure output of 1400 psi with a 1" bore master cylinder. This pressure level will work great for four wheel disc systems on heavier cars and trucks."
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Old 02-02-2009, 11:47 AM
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Well, it looks like a 9" booster for the truck. A 7 or 8" should work for my car...
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Old 02-02-2009, 03:55 PM
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Quote:
Originally Posted by staleg
And then of course you have the reverse mount 90 degree underdash version, too.
Like the 80s Dodge vans had?
Shane
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Old 02-04-2009, 08:00 PM
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I can tell you that I started out with a 7" single diaphragm booster that came with the power disc conversion kit for my '58 Chevy. It was NOT adequate!!! I upgraded to a 8" dual diaphragm booster, & it made a BIG difference!
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Old 02-04-2009, 08:35 PM
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Quote:
Originally Posted by 58biscayne
I can tell you that I started out with a 7" single diaphragm booster that came with the power disc conversion kit for my '58 Chevy. It was NOT adequate!!! I upgraded to a 8" dual diaphragm booster, & it made a BIG difference!
Cool--Thanks. You would be the first to even reply to a question like "Who has used both on the same car"
But alas--cannot go to an 8"

With a 454 and a Hydraulic clutch---I am pinched for space.
Only about 1/8 clearance between the clutch master and the booster
Maybe a 1/2" to the valve cover.

With 4-whl disc---I could use all the help I can get
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