Convert to Dual-circuit master cylinder?


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Post Sat Dec 15, 2018 8:51 am

Convert to Dual-circuit master cylinder?

I have a '60 B112 pickup with drum brakes front and back, and would like two brake circuits for safety. Can I use a master cylinder from a vehicle that has front discs and rear drums? Would I just need to insert a proportioning valve? Thanks - Mike
    1960 B112 V8 stepside
    1966 Triumph TR4A IRS
    1993 Miata LE -- daily driver

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Post Sat Dec 15, 2018 9:46 am

Re: Convert to Dual-circuit master cylinder?

No, you need a master for drums all around with rpcv (residual pressure check valve) in both outlets. Proportioning valves are used when there are disks in front/drum in rear to reduce pressure to the rear to prevent lock on light to medium brake applications. With drums all around they aren't required.
You need to select the master carefully to match the original bore and stroke (volume) and not just look at will it fit the hole.

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Post Thu Dec 20, 2018 6:20 pm

Re: Convert to Dual-circuit master cylinder?

I'm following this conversation, let me know what you find.

Thanks

Golden Jubilee
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Post Thu Dec 20, 2018 7:52 pm

Re: Convert to Dual-circuit master cylinder?

I would be looking for a dual master cylinder from a Ford or GM pickup with four wheel drums. I would think the better advice would be to try and match the master cylinder to the brakes. The diameter of the master piston should have a ratio match to the wheel cylinders. You will need this to maintain similar pedal pressure under stopping conditions. EZ stuff and some simple math.
CB89 mentioned residual check valves in the brake lines. I use them and I will never be without a RCV again. For the bother of installing them, you will get instant pedal response. The "daze" of a low OMG pedal will be gone.
I have not looked, but I would be surprised if there were no circuit diagrams on the internet. You Tube may have a how to video.
Like B72 might say, "This is not rocket surgery."
https://www.speedwaymotors.com/
http://www.ecihotrodbrakes.com/brake_facts.html
http://www.how-to-build-hotrods.com/brake-system.html
[b] I would rather have tools I do not need than to need tools I do not have

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Post Mon Dec 31, 2018 7:57 am

Re: Convert to Dual-circuit master cylinder?

Thank you, Nikki and Cornbinder. This points me in the right direction.
    1960 B112 V8 stepside
    1966 Triumph TR4A IRS
    1993 Miata LE -- daily driver

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Post Mon Jan 14, 2019 4:04 pm

Re: Convert to Dual-circuit master cylinder?

Mike-
Have you made any progress? I'm thinking of trying this in the spring on my A-102. Right now, it doesn't look like I can find a dual master cylinder with 3 mounting bolt holes. I may need to make an adapter plate to convert from 3 to 2 hole. Hopefully, if I find a new master with matching bore and stroke I can just use a longer pushrod to compensate for the plate.

Steve

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Post Mon Jan 14, 2019 4:46 pm

Re: Convert to Dual-circuit master cylinder?

I don't recall on the A series, or maybe it was the B series that went to the firewall mounting.

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Post Tue Apr 16, 2019 9:28 pm

Re: Convert to Dual-circuit master cylinder?

longrifle100,
Life got in the way, so I am just now getting back to looking at the brakes on my B112. I did get a mounting bracket for the booster and MC from a '72 IH pickup. It will act as a stand-off for the new unit. In a few weeks I'll get started on the engineering and planning. I hope.
    1960 B112 V8 stepside
    1966 Triumph TR4A IRS
    1993 Miata LE -- daily driver

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