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Typical 55-56 Mopar Brake Master Cylinder Push-rod travel?
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56D500boy
Posted 2020-12-21 10:00 PM (#606959)
Subject: Typical 55-56 Mopar Brake Master Cylinder Push-rod travel?



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I am starting a brake project (more details to follow soon). I discovered this afternoon, that with the pedal travel at about 4.5", the distance that the brake push rod would move would be about 2.25" (the math is probably there staring me in the face, I am just too lazy at this moment to do measure all the components and do the math). However, more importantly, I have no clue what the typical maximum master cylinder piston travel is supposed to be (hopefully less than 2.25")

Can somebody please enlighten me?

Thanks in advance.

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56D500boy
Posted 2020-12-21 11:15 PM (#606961 - in reply to #606959)
Subject: RE: Typical 55-56 Mopar Brake Master Cylinder Push-rod travel?



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From the recent/on-going "Single to Dual" thread, I found this:

wizard - 2020-12-03 12:05 AM
So, since this got me curious I went out and checked some spare parts and came to some conclusions:
The oem master cylinder has a diameter of 1-1/8" (28,575mm) and a maximum stroke of approximately 1.150" (29mm), supplying a displacement of 18,6 cm³
The oem wheel cylinder has a diameter of 1-1/8" (28,575mm)
Ratio 1:1


I like that answer.

Are there more examples (longer? shorter?)?

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Powerflite
Posted 2020-12-21 11:26 PM (#606962 - in reply to #606959)
Subject: Re: Typical 55-56 Mopar Brake Master Cylinder Push-rod travel?



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You're asking for a lot of details without giving any details. Which pedal assembly are you referring to? Power or manual? They are different from each other. Which master are you referring to for the max travel? They are all different from each other or are you wanting it for the stock one? The math for the pedal involves measuring the distance from the pedal bolt to the rotation point and dividing that number by the distance from the push rod to the rotation point. That is your multiplication factor for travel distance and force. The remote master that I use has a max stroke of 1.55". You can look up the number for yours, or just measure it, if you have one handy.
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56D500boy
Posted 2020-12-22 2:15 AM (#606964 - in reply to #606962)
Subject: Re: Typical 55-56 Mopar Brake Master Cylinder Push-rod travel?



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Powerflite - 2020-12-21 8:26 PM
You're asking for a lot of details without giving any details. Which pedal assembly are you referring to? Power or manual?


I'm going to give lots of details tomorrow (Tuesday) in a different thread. I want to present the info in a logical manner and this is taking some time to organize the photos and diagrams.

The pedal assembly is from a 1955 Chrysler and with the 1639 515 Power Brake System (the Kelsey-Hayes PB booster that was only used in 1955). I want to use this pedal assembly because it mounts the master cylinder (and Power Brake booster) up high, well above my 315 hemi rocker cover. I am not using the Kelsey-Hayers PB booster and plan to use Drum/Drum dual master.

This is the guts of the multi-link brake pedal system from the 1639 515 power brake assembly with some measurements that I took today. (More info tomorrow).





Edited by 56D500boy 2020-12-22 11:37 AM




(55ChryslerPowerUnit1639515Diagram.jpg)



(55ChryslerPowerBrakePedalArrangement_MovementMeasurements.jpg)



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Attachments 55ChryslerPowerUnit1639515Diagram.jpg (79KB - 264 downloads)
Attachments 55ChryslerPowerBrakePedalArrangement_MovementMeasurements.jpg (174KB - 270 downloads)
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56D500boy
Posted 2020-12-23 1:39 PM (#607004 - in reply to #606959)
Subject: RE: Typical 55-56 Mopar Brake Master Cylinder Push-rod travel?



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Does this photo of the pistons from a Disc/Drum Dual master (posted by Dels56, thanks Del) help me figure this out? For scale, Del has said that the piston diameter is just over 1".

To me it looks like the front piston (for the rear brakes) has a length of about 1.5" (?). The rear piston is longer but that's because it's for the front disc brakes and they need more fluid volume. The front piston is the one that would govern the maximum piston travel distance.

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Powerflite
Posted 2020-12-23 2:58 PM (#607012 - in reply to #606959)
Subject: Re: Typical 55-56 Mopar Brake Master Cylinder Push-rod travel?



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There are two versions of that master. One has 15/16" bore and the other is 1 1/32" bore. I don't know the stroke, although I could measure it as I have one on my white Fury.
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56D500boy
Posted 2020-12-23 4:24 PM (#607015 - in reply to #607012)
Subject: Re: Typical 55-56 Mopar Brake Master Cylinder Push-rod travel?



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Powerflite - 2020-12-23 11:58 AM
There are two versions of that master. One has 15/16" bore and the other is 1 1/32" bore. I don't know the stroke, although I could measure it as I have one on my white Fury.


Del told me that "My master is 1.032” ". So not the 15/16" one. I will be using a drum/drum master so exact distances are not necessary at this point. I just want to know that less than 2.25" will be good because I think that for a 56 Dodge the maximum peddle travel with the stock accordian PB system is about the same as I am finding with this 55 PB pedal system (4 5/8" vs about 4.5").



Edited by 56D500boy 2020-12-23 5:07 PM




(BellowsTypePowerBrakeMechanism.jpg)



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Attachments BellowsTypePowerBrakeMechanism.jpg (160KB - 284 downloads)
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dels56
Posted 2020-12-23 5:56 PM (#607021 - in reply to #606959)
Subject: Re: Typical 55-56 Mopar Brake Master Cylinder Push-rod travel?


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Hi 56D500 boy, I did find one note in my book as to the approx stroke of the Dorman M88787 Master cylinder, 1.550"

Now for any one else looking at this, I was advised to use DOT 5 silicone brake fluid by the auto parts store but recently I have read that this is a NO, NO with this master cylinder and also with the OE rear wheel cylinder. Dave may like this answer also.

Del
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56D500boy
Posted 2020-12-23 9:32 PM (#607029 - in reply to #607015)
Subject: Re: Typical 55-56 Mopar Brake Master Cylinder Push-rod travel?



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I was out in my un-insulated 12 x 20 garage (which, after 5 hours at 3000W (overhead 3000/4000/5000W 240V heater) was up to a nominal 18C (about 64F) from 5C (about 41F) inside (2C (35F-ish) outside) to do a little work on my 56 Dodge shifter pod/dash project this afternoon for a bit. While I was under the dash, I measured the rough distances involved in the current PB set up and single channel MC.

Distance from the pedal pivot to the bolt through the pedal = about 12". Distance from the MC activation arm to the same pedal bolt, about 9.25". So the distance from the pedal pivot to the MC activation arm = about 2.75". This math isn't 100% perfect but, on a straight ratio basis, for 4 5/8" pedal travel, the MC activation arm would move about 1.1". I think that I am in business.

The 5.5" measurement is for a related future project mock-up.



Edited by 56D500boy 2020-12-23 11:30 PM




(BellowsTypePowerBrakeMechanism_Annotated.jpg)



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Attachments BellowsTypePowerBrakeMechanism_Annotated.jpg (162KB - 278 downloads)
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samstrader
Posted 2020-12-23 9:41 PM (#607030 - in reply to #606959)
Subject: Re: Typical 55-56 Mopar Brake Master Cylinder Push-rod travel?


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I have been following this brake work too from Del and Todd. Del said he used a Chrysler Imperial 1970 master cylinder. I looked this up on Rock Auto and it has a 1 1/8 bore which I think is what was needed to keep the pedal from going down so far. Not sure what you are planning but just wanted to point out that Del found a master cylinder with a 1.125 bore...
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dels56
Posted 2020-12-23 9:48 PM (#607031 - in reply to #606959)
Subject: Re: Typical 55-56 Mopar Brake Master Cylinder Push-rod travel?


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I used a 1976 Dodge Dart master cylinder from Dorman Products, pt nbr M88787 1.032” bore.
Del S
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dels56
Posted 2020-12-23 9:50 PM (#607032 - in reply to #606959)
Subject: Re: Typical 55-56 Mopar Brake Master Cylinder Push-rod travel?


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I used a 1976 Dodge Dart master cylinder from Dorman Products, pt nbr M88787 1.032” bore.
Del S
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Powerflite
Posted 2020-12-24 12:00 AM (#607040 - in reply to #606959)
Subject: Re: Typical 55-56 Mopar Brake Master Cylinder Push-rod travel?



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If you are going to change it, you could also change it to use an electric booster instead of vacuum. Not a bad option because you could keep it hidden.
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dplotkin
Posted 2020-12-24 7:46 PM (#607071 - in reply to #607030)
Subject: Re: Typical 55-56 Mopar Brake Master Cylinder Push-rod travel?


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samstrader - 2020-12-23 9:41 PM

I have been following this brake work too from Del and Todd. Del said he used a Chrysler Imperial 1970 master cylinder. I looked this up on Rock Auto and it has a 1 1/8 bore which I think is what was needed to keep the pedal from going down so far. Not sure what you are planning but just wanted to point out that Del found a master cylinder with a 1.125 bore...


Believe you confuse Del with Dan. I'm Dan. I'm the guy who is using a 1970 Imperial master on a Chrysler 300 F. The Dodge Dart master is too long to clear the carb.

Dan
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dels56
Posted 2020-12-28 6:16 PM (#607211 - in reply to #606959)
Subject: Re: Typical 55-56 Mopar Brake Master Cylinder Push-rod travel?


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Dorman Master Cylinder M71297. 1.125" Bore

Del
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56D500boy
Posted 2020-12-30 2:49 PM (#607267 - in reply to #607029)
Subject: Re: Typical 55-56 Mopar Brake Master Cylinder Push-rod travel?



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Typical (for me): While looking for something not that important, I happen upon a diagram that I have been looking for somewhat desparately: The 1955 Mopar Power Brake pedal arrangement diagram (with notation on the maximum pedal travel). 6 inches would be about 3" at the booster. Way more than the 1.5"+/- that the master cylinder really needs.

The corresponding 55 Manual brake pedal arrangement, to me, shows that, in 1955, the basic pedal bracket and pedal were the same for the power brake and manual systems (with obvious deletions and additions, as needed). The manual brake pedal arrangement shows the return spring and the rubber stop that I am missing and still need to chase down.





Edited by 56D500boy 2020-12-30 2:54 PM




(55ChryslerPowerBrakePedalDiagram.jpg)



(55ChryslerPowerBrakeDiagrams_4.jpg)



(55ChryslerManualBrakePedalDiagram.jpg)



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Attachments 55ChryslerPowerBrakePedalDiagram.jpg (85KB - 268 downloads)
Attachments 55ChryslerPowerBrakeDiagrams_4.jpg (94KB - 268 downloads)
Attachments 55ChryslerManualBrakePedalDiagram.jpg (95KB - 272 downloads)
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Powerflite
Posted 2021-05-03 11:04 AM (#611669 - in reply to #606959)
Subject: Re: Typical 55-56 Mopar Brake Master Cylinder Push-rod travel?



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Something that was very interesting to me about this setup is, that this same '55 power booster was used on the '56 cars if you ordered power brakes with a manual transmission. I had wondered how they made that happen because I have never seen a clutch setup that would be compatible with the power brake pedal that's required for the accordion style booster. I am still wondering how they did it for the '57-up cars, or if they even had power brakes as an option for manually shifted cars at all.
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