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Questns about switchng MC, avoid 5port Jun block

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1958 rambler super View Drop Down
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    Posted: Nov/19/2022 at 6:36pm
Ok, the single piston MC I have has a huge 5/16 line coming from it, supplying fluid to a five port junction block, then the other lines going to the wheel cylinders are 3/16 line. I think I've wrecked the five port Junc block, galvins site says they have one but their sometimes wrong about what stock they have and they are shut down right now anyways.
There is a five port Junc block on inline tube website, theres no specs on it...

Would I be able to just switch the MC to a dual mc that the 3/16 brake lines connect to for the front and read brake lines? Removing the huge hard to bend 5/16 size hard line leading to a hard to find five port junction block that has a NPT port for the stop light switch....
Would a dual MC need to be connected to a proportion valve to work properly on my manual drum drum brake system that originally uses the single pist MC.??
Woukd I be able to select a manual dual MC, that is not power and does not connect to and work with a vacuum booster?
This is a great place to ask, while trying to do my own research.
Thanks guys! 


Edited by 1958 rambler super - Nov/19/2022 at 6:58pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Buzzman72 Quote  Post ReplyReply Direct Link To This Post Posted: Nov/19/2022 at 6:57pm
Just doing the math...the cross-sectional area of the 5/16" tubing is 0.981 square inches. 
And you want at least half that cross-sectional area for each of the two lines on a dual master cylinder. The cross-sectional area of 3/16" tubing is 0.589 square inches, so you're where you need to be. 

Next' determine what diameter line is required for your wheel cylinders. 

If they're 3/16", then you simply need two tee fittings with 3/16" inlets and outlets.  Run one line to front, then tee into the lines to each front wheel. From the other master cylinder port, run a single line to the rear, into the single flex hose, and then tee into the lines to the two wheel cylinders, along the rear axle housing. 

That way, you don't need a 5-port junction block; you only need two tee fittings, which are much easier to obtain.

Remember to bench-bleed your master cylinder before connecting to any new lines.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 1958 rambler super Quote  Post ReplyReply Direct Link To This Post Posted: Nov/19/2022 at 7:29pm
I've never worked with a dual MC, are the ports the size that accepts the nut on the end of the usual 3/16 standard, everyday sized brake line? The front port of the MC can go into a Tee that has three ports, one of which has a npt port for the stop light switch, I found one on inline tube website, that's for the rear brakes, because I think the front port of the mc is for the rear. Might have to do a fact check on that... 
So would the MC need to be a manual mc, or would a mc that was meant for power be able to be used?
Also, I was thinking I wouldn't need to bench bleed it? since all the lines are new and empty, the whole system is new. 


Edited by 1958 rambler super - Nov/19/2022 at 7:36pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Scrappy Quote  Post ReplyReply Direct Link To This Post Posted: Nov/19/2022 at 7:51pm
Originally posted by 1958 rambler super 1958 rambler super wrote:

I've never worked with a dual MC, are the ports the size that accepts the nut on the end of the usual 3/16 standard, everyday sized brake line?

There are plenty of adapters, so you will not have any issues attaching any size line to an MC.

Originally posted by 1958 rambler super 1958 rambler super wrote:

So would the MC need to be a manual mc, or would a mc that was meant for power be able to be used?

You would have to use a manual MC with a deep hole, as power MCs have a very shallow cone where the rod coming out of a booster goes.  If you try to use a power MC with a shortened manual rod, the rod could easily fall out of position.

Originally posted by 1958 rambler super 1958 rambler super wrote:

Also, I was thinking I wouldn't need to bench bleed it? since all the lines are new and empty, the whole system is new.

Bench bleeding, whether the system is new or not, will save you a whole lot of effort, especially since everything is empty.

I've gotten excellent service from Master Power Brakes when I've asked for tech information, or for recommendations.  They have a wide variety of MC styles and piston diameters, in both manual and power, so I would tell them what you're in need of and see what they have to say.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 1958 rambler super Quote  Post ReplyReply Direct Link To This Post Posted: Nov/19/2022 at 8:00pm
Ok I'll check them out, also, we'll, I guess they could answer this but I'll ask here anyhow, would it matter if the mc is for
 "disc drum" or "disc disc", not sure I'd easily or cheaply find a mc that was drum drum that wasn't nos and more expensive... 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Scrappy Quote  Post ReplyReply Direct Link To This Post Posted: Nov/20/2022 at 8:31am
Yes, it matters, as drum circuits contain residual pressure valves to enhance responsiveness.  A disc/disc MC might require a quick pump or two before maximum braking is available, which could be deadly in an emergency.

I doubt there's much difference in price, so I wouldn't worry over that.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Buzzman72 Quote  Post ReplyReply Direct Link To This Post Posted: Nov/20/2022 at 10:23am
You can buy the disc/disc master cylinder and add inline residual pressure valves. Speedway Motors sells them. 10 psi valves are for drum brakes, 2 psi valves are for disc brakes. If you decide later to convert to disc brakes, you can simply change out the RPV [residual pressure valve] on the proper line.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 1958 rambler super Quote  Post ReplyReply Direct Link To This Post Posted: Nov/23/2022 at 5:08pm
I was thinking of choosing this mc...    MC390360M...
 It's for drum drum. 
master power brakes sells it, even though the bolt holes don't completely match, I might be able to use the bottom holes, they do look like they are in a good spot for the opening of the firewall to accept the end of the mc and it might line up very well with the push rod connected to the pedal.
I think I'll have to see as I have it in hand... It's just one of those things, you have to have it to see if it'll work for the idea.
Here's the current brand new mc that might not get used... And the old junction block that's the problem.... 




Edited by 1958 rambler super - Nov/23/2022 at 5:28pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Scrappy Quote  Post ReplyReply Direct Link To This Post Posted: Nov/23/2022 at 5:19pm
Originally posted by 1958 rambler super 1958 rambler super wrote:

I was thinking of choosing this mc...    MC390360M...
 It's for drum drum. 

Make sure the bore diameter matches (or is very close) to what's in the car.  A smaller bore will make the brakes feel softer, a larger bore will make them feel harder; respectively, there will be more travel and less travel.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 1958 rambler super Quote  Post ReplyReply Direct Link To This Post Posted: Nov/23/2022 at 6:42pm
Ok, I just disassembled the old mc, looked at all the parts and realized I don't know what the "bore" size is... It's the thing that moves inside the inner diameter of the mc, when the push rod from the pedal pushes it, is that right? .... Meaning this mc has a 1 inch bore.... 



Edited by 1958 rambler super - Nov/23/2022 at 6:44pm
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