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Questns about switchng MC, avoid 5port Jun block

Printed From: TheAMCForum.com
Category: The Garage
Forum Name: Suspension, Steering, Brakes & Wheels
Forum Description: What makes it stop, turn, and smooths the ride
URL: https://theamcforum.com/forum/forum_posts.asp?TID=117620
Printed Date: Mar/29/2024 at 12:34am
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Topic: Questns about switchng MC, avoid 5port Jun block
Posted By: 1958 rambler super
Subject: Questns about switchng MC, avoid 5port Jun block
Date 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! 



Replies:
Posted By: Buzzman72
Date 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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Buzzman72...void where prohibited, your mileage may vary, objects in mirror may be closer than they appear, and alcohol may intensify any side effects.


Posted By: 1958 rambler super
Date 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. 


Posted By: Scrappy
Date 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 http://www.mpbrakes.com/" rel="nofollow - 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.


Posted By: 1958 rambler super
Date 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... 


Posted By: Scrappy
Date 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.


Posted By: Buzzman72
Date 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.

https://www.speedwaymotors.com/shop/speedway-residual-pressure-valves~8193-10191-652" rel="nofollow - Speedway Residual Pressure Valves (speedwaymotors.com)


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Buzzman72...void where prohibited, your mileage may vary, objects in mirror may be closer than they appear, and alcohol may intensify any side effects.


Posted By: 1958 rambler super
Date 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.... 




Posted By: Scrappy
Date 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.


Posted By: 1958 rambler super
Date 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.... 



Posted By: Scrappy
Date Posted: Nov/25/2022 at 10:30am
Yes, the diameter of the piston is the bore diameter. 


Posted By: 1958 rambler super
Date Posted: Nov/28/2022 at 6:33pm
Here's the new mc I'm going to try and work with, the bolt holes are maybe 3inches and 1/4 instead of the 3inches and1/8, the hole the push rod goes into looks the same, I havent stuck it in there to see if it's a good fit, ran out of time before I had to leave for work. 
there is a black rubber boot that came with the mc, the hole in the boot is super small compared to the push rod size that I'll be using, the same one that was used with the single mc already on the rambler. If the rod is just a little too big to go into the mc, I could get the rod lathed down by maybe 1/32 or 2/32, just to make sure it won't bind as it moves. 
I think I can open up the bolt holes on the mc a little and make it work, and use the two bottom holes in the firewall, but the dual mc is alot heavier then the single and hope the two bolts will be enough to hold it as time goes on.
The front port is 1/2
The back port is 9/16
Tomorrow I'll look at some adapters or reducers to connect the 3/8 nuts into those ports, and also a npt three way for the stop light switch. 


Posted By: nickleone
Date Posted: Nov/28/2022 at 7:55pm
Cut the rubber boot not the push rod.  I have had a similar MC on my 62 Classic, enlarge the mounting holes, I did no problem for the last 12 years using 2 studs with nuts.

Nick Leone


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nick
401 71 Gremlin pro rally car sold
390 V8 SX/4 pro rally car sold
1962 Classic SW T5 4 wheel disc brakes


Posted By: 1958 rambler super
Date Posted: Nov/28/2022 at 8:19pm
Oh! I think you got the wrong idea, I meant lathe down the push rod so it won't bind in the piston of the mc, and that's good news the two bolts will be enough to hold it no problem.
Wait a minute... You said use two studs with nuts.... I can't do that, (of course I can, just read on....) because there is threaded nuts welded on the other side of the firewall to accept the smaller size of stud used with the original, smaller mc, I'm sure the holes on this new mc are meant for studs little bigger (might have to do a fact check on that) and I would need to drill out the square nut to use the larger stud and nut... Did you mean "enlarge the mounting holes" of the mc, or the firewall? 
Also I was going to use the old rubber boot that's still on the push rod. 
Wait a minute... That rod moving back and forth wouldn't bind, because it wouldn't move back and forth in the piston, it's the piston that will be moving in the bore of the mc, being pushed by the driver at the brake pedal, and being pushed back by the spring in the bore of the mc. 
I geuss the only problem could be is to make sure the alignment of the piston for the push rod is not a problem.. 


Posted By: nickleone
Date Posted: Nov/30/2022 at 2:31pm
Enlarge the mounting holes on the MC.  Use the studs that came with the firewall mounting for the original MC

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nick
401 71 Gremlin pro rally car sold
390 V8 SX/4 pro rally car sold
1962 Classic SW T5 4 wheel disc brakes



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