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Master cylinder differences.

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Doober View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Doober Quote  Post ReplyReply Direct Link To This Post Topic: Master cylinder differences.
    Posted: Sep/30/2022 at 8:22pm
Is there a difference between a manual disc master and a power disc master? Are the mounting hose spaced at different lengths? Are there any other differences? Needing the manual disc master for my 69 Rebel.
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tomj View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tomj Quote  Post ReplyReply Direct Link To This Post Posted: Sep/30/2022 at 10:59pm
This could/should be in suspension and brake... No problem though. 

Disc to drum, same principles same master cyl same mounting. However, drum masters have a little check valve, a spring and plunger, hidden under the brass cone inside each output port. 

You can convert a drum master to disc put extracting it. The trick is to use a small sheet metal screw to grip the inside of the hole, just enough to pull it out. Use two screw drivers, one on each side under the head to lever it out. Extract spring and plunger and push it back. 

Do that for the front circuit only unless you have disc rears (not AMC)
1960 Rambler Super two-door wagon, OHV auto
1961 Roadster American, 195.6 OHV, T5
http://www.ramblerLore.com

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Post Options Post Options   Thanks (0) Thanks(0)   Quote sweatlock Quote  Post ReplyReply Direct Link To This Post Posted: Oct/01/2022 at 6:26am
The OP is asking about the difference between the master cylinders for manual and power disc brake applications. 
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scott View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote scott Quote  Post ReplyReply Direct Link To This Post Posted: Oct/01/2022 at 7:11am
In 1969 there was no manual disc brake master cylinder. Power discs only.

Starting in 1971, you could get manual discs.

Tell us more about what you are trying to do. Convert a manual drum car to discs? Convert a power disc car to manual disc? What disc brake setup are you using??
"Prolly" is not a word.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ramblinrev Quote  Post ReplyReply Direct Link To This Post Posted: Oct/01/2022 at 7:17am
Scott has it right.
And when there was the option of manual or power disc, they are different master cylinders.

74 Hornet Hatchback X twins (since 1977)
62 American Convertible (still worth the $50 I spent in 1973!) AMCRC #513, AMO #384
70 AMX 360 4-speed (since 1981)
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tomj View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tomj Quote  Post ReplyReply Direct Link To This Post Posted: Oct/01/2022 at 9:59pm
Originally posted by sweatlock sweatlock wrote:

The OP is asking about the difference between the master cylinders for manual and power disc brake applications. 

I was too long winded -- the difference between drum and disc masters is the presence of the check valve on drum masters. Remove that and a drum master cyl becomes a disc master.

Therecl may be cases when disc and drum specify different masters if bore or other features change.
1960 Rambler Super two-door wagon, OHV auto
1961 Roadster American, 195.6 OHV, T5
http://www.ramblerLore.com

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sweatlock View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote sweatlock Quote  Post ReplyReply Direct Link To This Post Posted: Oct/02/2022 at 6:45am
I re-read your response and you are correct, my mistake. 

Another difference is that the reservoirs are different sizes on a disc brake master cylinder (volume) and on a drum brake master cylinder they’re the same size. 


Edited by sweatlock - Oct/02/2022 at 8:22pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mbwicz Quote  Post ReplyReply Direct Link To This Post Posted: Oct/02/2022 at 6:53pm
Just a couple of questions to the experts:

- I would expect that the leverage would be different on a manual master cylinder.  Either a smaller bore master cylinder or a different brake pedal.  Did AMC do either of these?

  I'm just thinking about the initial question, if the OP wants to take a PDB car and go to manual brakes, would he need to change the MC?  Maybe his booster went bad and he just wants to run manual discs.

Thanks,
Mike
1970 AMX, one step forward, one step back. Both steps cost time and money.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Doober Quote  Post ReplyReply Direct Link To This Post Posted: Oct/08/2022 at 5:17pm
So, if I got a 1971 manual disc master. Would it fit a 69 Rebel that was fittedwith manual drums? Would the stubs spacing be the same? I am converting my manual drums to manual disc.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ramblinrev Quote  Post ReplyReply Direct Link To This Post Posted: Oct/08/2022 at 8:03pm
You're probably going to have to try it and see. Buy it and compare. Return if it doesn't match the studs.
74 Hornet Hatchback X twins (since 1977)
62 American Convertible (still worth the $50 I spent in 1973!) AMCRC #513, AMO #384
70 AMX 360 4-speed (since 1981)
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