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#922061 - Fri Feb 22 2013 12:27 PM 1957 Chevy Pickup - Dual Master Cylinder Issue
VanattiWorkshop Offline
Wrench Fetcher
Registered: Thu May 03 2012 09:50 PM
Posts: 68
Loc: USA - East
Hi all!

I've had my dual master cylinder mounted for a few months now and finally got ready to go buy brake lines, when I realized I had a problem! My dual master cylinder, that I bought to replace the original, has 4 ports!

I bought this one, apparently by accident: http://www.americanclassic.com/images/BR0129.jpg

It says it's a "1936-1991 Master cylinder, dual reservoir, 1 inch bore, two 3/8 inch ports on each side (total of 4 ports), has deep bore with metal insert for both manual and power applications".

My truck has 4 drum brakes and no prop valve. Am I out of luck? I was considering running a line out of each port, directly to each wheel because I've read that drum cylinder's are metered at the port and don't use a prop valve but I have no idea about brake systems and why that would / wouldn't work.

I've goggled a bunch of various terms but can't find a solution. I'd really prefer not to have to order another one if possible. Any ideas?
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1957' Chevy Pickup
My welcome thread: Introduction and Story
My Album: 57' Chevy 3100 W/235
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#922066 - Fri Feb 22 2013 12:49 PM Re: 1957 Chevy Pickup - Dual Master Cylinder Issue [Re: VanattiWorkshop]
Pre '68 Dave Online
Shop Shark
Registered: Mon Jan 08 2001 12:00 PM
Posts: 4121
Loc: Snohomish,WA,USA
That cylinder is for multi use. Just plug the ones on the side you do not use.
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#922067 - Fri Feb 22 2013 12:50 PM Re: 1957 Chevy Pickup - Dual Master Cylinder Issue [Re: VanattiWorkshop]
3B Offline
Shop Shark
Registered: Wed Nov 09 2005 12:00 PM
Posts: 4793
Loc: B. C. Canada
Hy VanattiWorkshop, Don't panic, plug the two ports in the master cylinder which are more difficult to reach and plumb to in the truck. Now you can plumb the truck using the primary (the port closest to the pedal) to plumb to front brakes, and the secondary port to plumb the rear system. You can follow the factory plumbing, other than not connecting the front and rear systems. You should not need a proportioning valve for an all drum system. You will have to find out if your master cylinder was designed for drum, disc, or a disc/drum system, if it was for a disc or a disc/drum system you will have to install 10 p.s.i. residual pressure valves in the ports designed for disc brake use, hope that helps.
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#922070 - Fri Feb 22 2013 12:55 PM Re: 1957 Chevy Pickup - Dual Master Cylinder Issue [Re: VanattiWorkshop]
VanattiWorkshop Offline
Wrench Fetcher
Registered: Thu May 03 2012 09:50 PM
Posts: 68
Loc: USA - East
Unfortunately, I've read the manual and the website I bought it from, and can't seem to find if it's drum only or disc/drum. Still, that helps so much that I can just plug the unused ports.

Out of curiosity, what would happen if I ran a line from each port to each wheel? Uneven braking I'm guessing?

That's fantastic though, I can still go buy my lines. Thanks guys!
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1957' Chevy Pickup
My welcome thread: Introduction and Story
My Album: 57' Chevy 3100 W/235
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#922082 - Fri Feb 22 2013 01:31 PM Re: 1957 Chevy Pickup - Dual Master Cylinder Issue [Re: VanattiWorkshop]
truckernix Offline
Registered: Sun Mar 24 2002 12:00 PM
Posts: 8283
Loc: Bracebridge Ontario Canada
So how does one plug a port?

If you hooked up all four in such a way that one side was on one chamber and the other side was on the other, it would be really bad in a failure mode.


Edited by truckernix (Fri Feb 22 2013 01:34 PM)
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#922112 - Fri Feb 22 2013 03:36 PM Re: 1957 Chevy Pickup - Dual Master Cylinder Issue [Re: VanattiWorkshop]
3B Offline
Shop Shark
Registered: Wed Nov 09 2005 12:00 PM
Posts: 4793
Loc: B. C. Canada
Hy Guys, in theory you could indeed use all four ports on the master cylinder, you would just need to use the two primary ports for the front brakes, and the two secondary ports for the rear brakes. You would have to run more tubing, and add another rear flex line if you did do it that way, sounds like a lot of extra work to me. As to pluging the ports, you just need to use an inverted flare plug of the correct size, Weatherhead p/n 131X?, you may have to purchase port adapters to convert the ports to a standard size because the modern master cylinders have all kinds of different size tube nuts goin into them, hope that helps.
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#922161 - Fri Feb 22 2013 11:48 PM Re: 1957 Chevy Pickup - Dual Master Cylinder Issue [Re: VanattiWorkshop]
truckernix Offline
Registered: Sun Mar 24 2002 12:00 PM
Posts: 8283
Loc: Bracebridge Ontario Canada
I guess you will want to make sure that there are residual valves in your system. I don't know if they would have provided them inside your master.


Edited by truckernix (Sat Feb 23 2013 02:02 AM)
_________________________
1951 GMC 1 Ton Flatbed -- It is finally on the road and what a great time I have driving it!
1951 1 Ton Completed


My Chevy Master 4 Door is on the Road!
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#922388 - Sat Feb 23 2013 02:55 PM Re: 1957 Chevy Pickup - Dual Master Cylinder Issue [Re: VanattiWorkshop]
VanattiWorkshop Offline
Wrench Fetcher
Registered: Thu May 03 2012 09:50 PM
Posts: 68
Loc: USA - East
I think I'll go with the plug route since I already have 3 brake hoses and don't want to order another. I'll probably plug the left front and left rear since those are tucked on the inside of the frame and harder to get to.

Still not sure if I need prop / residual valves so maybe I'll just have to find out the hard way.
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1957' Chevy Pickup
My welcome thread: Introduction and Story
My Album: 57' Chevy 3100 W/235
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#922667 - Sun Feb 24 2013 02:03 PM Re: 1957 Chevy Pickup - Dual Master Cylinder Issue [Re: VanattiWorkshop]
3B Offline
Shop Shark
Registered: Wed Nov 09 2005 12:00 PM
Posts: 4793
Loc: B. C. Canada
Hy VanattiWorkshop, I sent an "E" mail to American Classic, trying to find out what the original application for the master cylinder was full disc, disc/drum, or full drum, I was answered by a budding politician, they said " Trick question. If you plumb it then yes it works for all". So I sent him another "E" mail asking them if their master cylinder p/n BRO129 had built in residual pressure valves. Their answer was "Another trick question. None of them do to my knowledge. You only need them really if you are sighting the master cylinder low under the floor and the fluid will run back. We sell a 2 and a 10 valve for that." So from that I would assume (and yes I know what we do when we do that) that BRO129 would require a 10 p.s.i. residual valve in the front and rear brake circuits. I was extremely disappointed with their response, drum brake master cylinders have residual pressure valves built into them, regardless of where on the vehicle the master cylinder is mounted. Hope that helps
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#923244 - Tue Feb 26 2013 09:59 PM Re: 1957 Chevy Pickup - Dual Master Cylinder Issue [Re: VanattiWorkshop]
Tiny_Jaime Offline
Shop Shark
Registered: Tue Aug 07 2012 07:19 AM
Posts: 582
Loc: Henderson, Nevada
I just purchased one from ebay for my 56 3100 chevy. It looks identical to that picture here. My came with two plugs. My dirrections says add your brake lines, you may use either side of the master cylinder, plug off the other side with the enclosed plugs. Oh the only difference my has a booster on it. this one you have should be for a drum /drum set up because if you had disks you would need a proportioning valve. It also says the lines closest to the booster is for the rear and farthest away from the booster is for the front and the lines do cross each other, because it need to be plumbed this way as the master cylinder ports are staggered to get the front braked to hit first creating the dive you need.

good luck
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