Another Disc brake question.

WOT440

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Good morning, all. I'm considering doing a Scarebird front disc brake conversion on my 68 Newport. I have recently, within the last two years had my brake booster rebuilt,
(booster Dewey). It has less than 1k miles on it.
My question is...is it absolutely necessary to use a disc brake booster for this conversion? Has anyone used a drum brake booster with disc brake set up with success?
TIA. Appreciate all suggestions and opinions.





1965-72 Plymouth, Dodge C-Body full size front disc
 
Save yourself some grief and get the dual diaphragm booster when you install front discs. Here is the reason. Drum brakes require about 400 PSI and that is about all you can get from your single diaphragm booster. Discs require almost 900 PSI. Chrysler fixed this problem for us when they started using front discs.
Oh, and don't forget the proportioning valve either. There are tons of threads on this site dealing with this very problem.
I tried using my newly rebuilt drum booster just like you are planning. It will stop the car but I can guarantee you won't be happy with it.
 
Save yourself some grief and get the dual diaphragm booster when you install front discs. Here is the reason. Drum brakes require about 400 PSI and that is about all you can get from your single diaphragm booster. Discs require almost 900 PSI. Chrysler fixed this problem for us when they started using front discs.
Oh, and don't forget the proportioning valve either. There are tons of threads on this site dealing with this very problem.
I tried using my newly rebuilt drum booster just like you are planning. It will stop the car but I can guarantee you won't be happy with it.
Exactly what I was looking for. Thank you.
 
When I first found the Scarebird website and "upgrades", I thought it was neat to find somebody who was using "auto supply" parts rather than used parts from a salvage yard. Things one could go down ant order rather than messing with chiggers, grassburrs, and possible critters in the grass.

THEN, a few years later, I noticed that the recommendations had changed. Why? The aftermarket has ceased to support them! Normal thing, sales volume drops and as inventories deplete, no new batches of parts are produced, just line the OEMs do.

Over the decades, there were things that were "everywhere" on lots of cars, then the car platforms changed and something else, "everywhere" replaced the earlier parts. H78x14 tires was the first one, it seemed. Drum brake drums, etc.

Just something to think about for down-the-road with Scarebird conversion items. I'm not against his concept, just the realities of such.

CBODY67
 
As far as I was aware, the size master cylinder was more important than the booster in regards to building the neccessary pressure! The booster is there to assis your foot and thats where you have to decide if you are okay "having to step on it harder" or to have a "soft and mushy pedal".
 
Yup, use the disc booster, 1000% for the reasons above, PLUS this:

If for some reason you're involved in an accident where a serious injury or death occurs, and in the investigation to determine why, and it's determined that you did the work on your car (as an unlicensed mechanic), and perchance there are questions regarding the braking performance and therefore the braking system is inspected and it is discovered that a drum booster was used in place of the correct disc booster, the lawyers will have a field day.

Yes there will be people who say their drum booster works fine on their disc system, and all power to them. I tried it and it was shyte. Disc booster made all the difference, plus I had comfort that in a panic situation, maybe my car's braking performance with the correct parts will mean that 20' stopping difference than means NOT killing the idiot on the bicycle that rode out in front of you.
 
But then you could argue that the drum booster would still provide upgraded brake power to the disc brakes over manual drums, plus the accuser would need to prove that this was cause of the accident. Forensic testing of the brake force and so on would then determine if there was something wrong with it. But that would mean that the justice system would work and not simply create a witch hunt without any evidence like they usually do.

Mechanics aren't neccessarily "licensed", I could literally go and apply at a shop and be a mechanic so I don't know if that argument holds. Some places only hire you with the SAE certification, sure but most around here don't require it. I also have seen more "trash" done by "licensed mechanics" than others. We actually care about our vehicles, the person you pay to work on them does not, and only does it for the money, not the passion. Having someone else install the kit, I would personally expect that the bolts get left loose... just as a perspective from what I have seen before.

Still, I would do it correct and use the correct booster for the discs. Booster really is just an assist to your force on the foot. As far ad I am aware, there is no "requirement" to have that and it sort of falls under the "creature compfort" as I understand it. Anyway, do it the right way lol.
 
Yup, use the disc booster, 1000% for the reasons above, PLUS this:

If for some reason you're involved in an accident where a serious injury or death occurs, and in the investigation to determine why, and it's determined that you did the work on your car (as an unlicensed mechanic), and perchance there are questions regarding the braking performance and therefore the braking system is inspected and it is discovered that a drum booster was used in place of the correct disc booster, the lawyers will have a field day.

Yes there will be people who say their drum booster works fine on their disc system, and all power to them. I tried it and it was shyte. Disc booster made all the difference, plus I had comfort that in a panic situation, maybe my car's braking performance with the correct parts will mean that 20' stopping difference than means NOT killing the idiot on the bicycle that rode out in front of you.
Different perspective but valid point. Main objective is safety above all. Thanks for that.
 
As far as I was aware, the size master cylinder was more important than the booster in regards to building the neccessary pressure! The booster is there to assis your foot and thats where you have to decide if you are okay "having to step on it harder" or to have a "soft and mushy pedal".
The Master cylinder size is important in the manner of how much pressure is transferred to the brake fluid but is only part of the formula. Here is the formula for figuring out what you need......... Say you have an 8" single diaphragm booster and a master cylinder with a 1" bore.
The formula works like this. 4" X 4" x 3.14=50.24 square inches X 8 =401.9 pounds of force. Your 1" master cylinder has .78 square inches. You divide the 401.9 by .78 giving you 515.2 lbs of output force. That is all you get no matter how hard you stomp on the pedal.
Now say you have a dual diaphragm 8" booster. That doubles the 401.9 to 803.8 pounds of force. Divide that by .78 gives you 1030.5 pounds of output force.
If you have a 3/4" bore you have .44 you get more force yet. With the dual diaphragm 8" booster you get 803.8 divided by .44 gives you 1826.8 pounds of force.
With this information, it is easy to see why a single 8" booster is good enough for drum brakes that require around 400 PSI. Disc brakes require closer to 900 PSI. That is why the manufacturers stepped up to the dual 8" diaphragm with a 1" master bore.
I had to learn this lesson the hard way just like many of us that try to mix match parts that will not work together.
 
But then you could argue that the drum booster would still provide upgraded brake power to the disc brakes over manual drums, plus the accuser would need to prove that this was cause of the accident. Forensic testing of the brake force and so on would then determine if there was something wrong with it. But that would mean that the justice system would work and not simply create a witch hunt without any evidence like they usually do.

Mechanics aren't neccessarily "licensed", I could literally go and apply at a shop and be a mechanic so I don't know if that argument holds. Some places only hire you with the SAE certification, sure but most around here don't require it. I also have seen more "trash" done by "licensed mechanics" than others. We actually care about our vehicles, the person you pay to work on them does not, and only does it for the money, not the passion. Having someone else install the kit, I would personally expect that the bolts get left loose... just as a perspective from what I have seen before.

Still, I would do it correct and use the correct booster for the discs. Booster really is just an assist to your force on the foot. As far ad I am aware, there is no "requirement" to have that and it sort of falls under the "creature compfort" as I understand it. Anyway, do it the right way lol.
To me, the POINT is that IF Chrysler's performance standards could have been met with the drum brake power booster on power front disc brake vehicles, they would NOT have spent the money to put the dual-diaphram booster on the disc brake cars, period. It's about the total area of the diaphram(s) that makes it work.

In the Fuselage cars, they had more cowl real estate to support a larger diameter booster, but they still used the Midland-Ross booster for power drum brakes, as my '70 DH43 has on it, just like my '66 Newport Town Sedan has.

Many mechanics might not need to be "licensed" (dependent upon where they are located), but they CAN be certified in the brake system area of expertise by a 3rd party organization. By taking a test and having some experience in the particular area. Certainly, anybody can sign up for, pay the money, and take the test, to hopefully pass it. By observation, few people not "in the biz" do that, so that certification AND patch are "credentials", but have to be renewed every so often. OEMs have their own training programs, too. These things would be "credentials" of the fact "something was known about what was done". If a prosecuting attorney did not ask about related credentials, they would not be doing their job well. BUT of course, this is why we have insurance for such situations! Personal or business.

In the DFW area, tv and radio are full of "accident and injury" lawyers who have orchestrated $$million settlements for their clients. Usually from "big trucking firms", but they can direct their efforts to "little people", too. Just be aware of these things.

Disc brakes might be better in the mountains and from higher speeds, as to stopping and fade resistance, but in unexpected situations, it's still "that first stop" that is usually where things happen. In THAT scenario, the OEM drum brakes would lock all four wheels (or at least the rears) such that it was tires that made the difference, not the braking system itself. With the driver's skill in steering around the issue a plus (evasive maneuver).

It has always been my orientation to do "upgrades" with at least an OEM level of execution and parts as the best way to do things. Suspension parts, brake parts, engines, etc.

Respectfully,
CBODY67
 
Agreed with cbody67. I moved to the windy and mountainy west coast and the 4 wheel discs are a great upgrade here. Lime I daid, use the right components that are supposed to work together. If you want to be 100% correct, the wheel cylinder diameter and how many pistons your caliper has plays a role in the pressure department as well I found out!

Right Stuff G80011501: Brake Booster/Master Cylinder Combo Mopar - JEGS

This is what I am using for my all around discs and the stopping power is more than plenty! The only negative is that the bracket that holds it to the firewall is sort if flimsy making this entire contraption shake from vibrations. I'm going to have to reinforce the brackets a little soon.
 
To me, the POINT is that IF Chrysler's performance standards could have been met with the drum brake power booster on power front disc brake vehicles, they would NOT have spent the money to put the dual-diaphram booster on the disc brake cars, period.
Absolutely, I agree. Municipal, state/provincial laws aside re licensing, it's based on common sense.
 
just to throw a shovelfull of poo into the discussion...somewhere in this forum is a thread where the guy was removing the aftermarket conversion , which he hated, and going back to factory discs...I don't recall all the reasons....personally I'd try to find the stock 69-73 setup which we all know works...as far as the booster, you already own it ,so I would try it... my 68 had a Midland booster and has been stopping fine for over 20 years with a disc conversion, but I have no idea whether a Bendix one might not work as well...I'll also state that I've never driven a car with a dual diaphram booster so I can't tell you how much better it may stop
 
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There have been a number of similar statements - and it boils down to "factory engineering is best" for these braking systems hands down - at least, that's my opinion. Others may differ, and it's their right to disagree.

When you say your 68 has a Midland booster with a disc conversion - is it a drum booster, or the wider single diaphragm later issue disc booster? Regardless, if you're satisfied with the system...
 
I suspect that Chrysler's performance standards go FAR past "normal driving" situations. Which is what most of us normally do. In that case, a drum brake booster can appear to work well, but if in the same situation as the not-normal-use of Chrysler's standards, it would not be as good, which is where the dual-diaphram unit would be needed to meet those performance criteria.s

Many might not have experienced total brake fade, where no amount of pedal pressure will slow the vehicle. In these situations with power front disc brakes, where the rear brakes have completely faded, the front brakes are stopping the car and MORE pedal pressure would be needed. So, in that situation, all of the booster-added pressure would be good to have.

It was the practice to include a power booster with any front disc brake car in the 1960s and later. EXCEPT for 1970 Camaros which could have non-power brake front discs. I had a work associate who had one of those cars. I asked how much pressure it took to stop the car, which was driven in normal traffic uses. He replied "fine". At the time, he and his wife were in their 20s. FWIW

Enjoy!
CBODY67
 
Really don't know...this is the booster in question....it was on the car when I bought it 24 years ago...I just replaced the master with a 71 disc one and did the later discs...
0827241210.jpg
 
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It's 2024, the first thing 90% of people do after plowing into someone on the street is hang up and dial 911...

My first line of defense from litigation is my car... I'm so broke I'm driving a 70's land yacht..

The limiting factor of power vs non on these old cars is the length of the lever. Lots of performance cars use non power disc but they have high ratio foot pedals. I have been chastised before for calling into question the deities at the corporation so this is only an observation. When I was a kid I had two dodge trucks that were so over boosted in comparison to other cars that it took time to learn to drive them. When that young people always seem to be moving and when you are a kid with an 8' bed that doesn't have to be made, every other week somebody want to borrow your truck.
We had great fun watching the learners.
I was one house from the stop sign. That first one was a doosey.. they always thought it was them but at the second stop sign they looked back in disbelief and we would be rolling.

Good will to all and good thing for smart cars!
Pic by nephew, we were headed to swapmeet

62838.jpeg
 
The original 64 Chrysler drum power booster with 67 dual 1 inch drum master works very well on my 64 New Yorker with 78 Corboba 11.75-inch disc brakes in all street driving conditions. Haven't tried it yet with a 1.25 master.
Pedal modulation is very good and requires little effort to lock the disc at any sane speed. Haven't tried it at 80 and I'm not going to.
The 64 offered power or manual drum brakes. Both used a 1-inch master cylinder.
The 65 rare manual disc used a 1-inch master cylinder.

But this is a 64, not a 68.
 
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If I were you, I’d get the dual-diaphragm booster. If I were me, I’d keep using the original drum master, as I still am, on my ‘66 300 that I converted to ‘72 C-body discs, in the ‘80s.
 
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