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Brake boosters

Kern Dog

Life is full of turns. Build your car to handle.
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Hello,
A common upgrade for classic car owners is improved brakes. Like many of you, my car was originally a 4 wheel non power drum model.

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Within the first year of ownership, I swapped in a front disc setup from a 1975 Dart. 11” rotors, proportioning valve, 8 3/4” single diaphragm booster and 15/16” master cylinder. The car weighed 3660 lbs then and stopped quite well. Over the years I have made several changes including brake stuff. Currently I have that same A body booster but with an aluminum 15/16” master cylinder. I have 13” front rotors and calipers with 2 1.59” pistons. The rear is a 11.7 rotor with a single 1.5” piston.
The brakes are good but not great. I’ve been told that a B body dual diaphragm booster would be an improvement but have heard of a high failure rate with reproduction units.
Soooo…. I looked through my stash. I have a few different boosters from cars and trucks that I have parted out and am wondering if any of them would work.
First up for the purposes of a baseline is an A body unit similar to what I have in the car now.

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This measures 8 3/4” in diameter.
Next up is what looks like a dual diaphragm unit.

FC25710C-15C3-4E36-9D54-94ACEEC84BE3.jpeg
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It is unusual due to the strange placement of the check valve hole.
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The second booster is smaller in diameter.
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I suspect it may be from an early 70s power drum Valiant but I don’t know for sure.
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7” dual diaphragm??

Next is a power drum B body unit.

00293176-2959-4A2E-943D-D644A3E4C339.jpeg


I know that the drum units won’t work for me but I wanted to show it.
Finally are these two from 70s era Dodge trucks:

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Dual diaphragm, 8 3/4” diameter.
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Two bolt mount for a later model aluminum master cylinder too. Notice how trucks have the reservoirs backwards.
I think the 4 bolts at the back are spaced different from the B body units though.

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Funny thing. Manual brakes straight to the master. Same on older Dodge trucks manual or power. No linkage.
 
My pick would be one of the truck dual diaphragm boosters. These were used originally only on 440 powered trucks for valve cover clearance. The small block and 400 powered trucks used the larger single diaphragm booster. Like you said, the reservoirs were reversed. And 2 bolt mounting.
 
The problem though is that the truck boosters have a 4 bolt firewall mounting pattern that is 3 1/2" apart while the firewall stiffening plate is 3 1/4" apart. I just noticed this after I made the second post here. I could oval out the holes but I'm not sure if I want to do that.
I was thinking that I could use what I have here.
A booster rebuild company like "Booster Dewey" would surely have a core charge if I didn't supply an exact model to send them.
 
I don't understand what you are trying to accomplish? Your first posting stated that, after the disc swap to the '75 A Body brakes, the car stopped quite well. But after more "improvements", the brakes are good but not great? You are fixing what wasn't broken?
 
Why don't you go to Hydro Boost and be done with it?
Mike
 
is the performance worse now as is or better than when you had stock A body set up?
The first change that I made was to the Dart booster, master cylinder and 11" front discs. The stock 10" rear drums were still in place. The car weighed 3660 lbs and still had the 318.
Yeah, it stopped quite well but this was over 20 years ago. What impressed me then may not impress me today.
The change to rear disc brakes in 2006 did not improve stopping ability at all. They didn't get worse though.
I'm just trying to get the brakes to impress me. I've driven manual disc/drum Dusters and Darts that inspire more confidence.
 
I’m definately no wizard on this stuff but if I recall it seems that when some go to rear disc as well as fronts is when they have lack luster performance, or as in your case performance that doesn’t meet their expectations. I can help but wonder if it the dynamics of having to push so much more fluid into a caliper as opposed to a wheel cylinder Is part of the cause. Also am thinking that the system is designed as ‘whole’ and that the engineers in charge are able to balance it all better as a complete solution from day one as opposed to what many enthusiasts do by adding a brand X here then a Brand Y two years later then throwing a brand A into the mix a year after that etc…. If that makes sense. Maybe if it were all one manufacture following their recommendations it would perform best? And they would be accountable too?

on my last car I tried the 15/16 bore aluminum master and chased a few lower pedal problems and then also faded pedal issues after it sat for more than a week. Always needing a pump to get full pressure and pedal and it was fine for the whole drive and the days following providing it was t too long. I ended up putting a inline residual pressure valve on the rear circuit of that car and I think that helped. on my current duster I think I will try a 1 1/32 bore master and see how that goes.. still not sure which way to go.

if anyone else reading this has tried the 1 1/32 bore in their A body and provide feedback as to its performance that would be appreciated too. It’s a manual brake application do to low vacuum.

Stick with it, chasing these brake issues is frustrating to say the least.
 
I’m definately no wizard on this stuff but if I recall it seems that when some go to rear disc as well as fronts is when they have lack luster performance, or as in your case performance that doesn’t meet their expectations. I can help but wonder if it the dynamics of having to push so much more fluid into a caliper as opposed to a wheel cylinder Is part of the cause.
This posting makes me think. You are pushing a larger volume of brake fluid into calipers as opposed to the smaller volume necessary for wheel cylinders. Is it possible that you may need steel brake lines and the rubber hoses with larger internal diameters to allow for the increased volume?
(I don't know, but am just asking the question....)
 
This posting makes me think. You are pushing a larger volume of brake fluid into calipers as opposed to the smaller volume necessary for wheel cylinders. Is it possible that you may need steel brake lines and the rubber hoses with larger internal diameters to allow for the increased volume?
(I don't know, but am just asking the question....)
If volume was the problem the pedal would go to the floor or down low and you would need another pump to increase the volume.
 
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