dual master cylinder swap

[rmk57]

Which is the simplest way to perform the this swap? I'm still going to use my original drum brakes so a proportioning valve shouldn't be needed. Would it be ok to just run the rear brake line right to the master cylinder and use the existing ports for the front brakes?

[Ford Blue blood]

Nope....might as well keep the jug on it.  This topic has been brought up before and using a dual master without the factory switch/proportioning valve is the same as having a single.

That ugly assembly has a piston in it that slides over and closes off the failed section of the brake system in adition to providing proportioning and a light on the dash that says you have a brake problem.  Without it there the center seal on the piston in the master never seats.  The only master cylinder that is a true dual master is the early 63 Vette.  It had two pistons (4 seals) that operated independently.

69/70 Mustang drum/drum will bolt up, get the valve for that car, same goes for the 76 Granada......

[rmk57]

I was going to run the rear brake line straight to the master cylinder by passing the original block and then use the extra port just for my front brakes. So in a
way the front and rear brakes would be separate in case of a master cylinder failure.

[Ford Blue blood]

You still have an in essence a single master.  The fact that there are only three seals in the assmebly is the root of the problem.  A sure way to test this out is to note when you bleed the brakes without the proper parts the pedel falls all the way to the floor, with the factory (or aftermarket) switch/proportioning valve in place you will note the pedel goes about 3/4 to the floor and then stiffens up.  After bleeding you will have to re-center the slider (turn off the brake warning switch) by going to the other end and cracking a bleed valve with slight pressure.  Easiest way to do this is hook a test light to the switch terminal and the battery and wait for it to go out.

If one of the seals in the master fails you loose everything, hence the need for an operating emergency brake.  A much more likely failure would be a ruptured flex line or a rusted hard line.

[rmk57]

I have 3 brake proportioning valves all from different year Fords. There all disc brake units and I would like to know if it would be ok to use one with my drum/drum brake 57 ? I do plan on a disc brake swap one day just not now.

[bagboy]

I used the brake line blockunder the drivers side cowl.With anew line you go to the front conection.And next put a plug in the block wherte the previous line went. You really don't need a sliding  warning switch. At least I think so ps  66mustang  works pretty good [sure aint power brakes]

[Ford Blue blood]

Yes you do not need the warning switch.......you need the slider!

[rmk57]

 I did some research on the porp valves I have on hand and the one I'm going to use is from a manual drum brake 1968 Galaxie part #C8AA...... There is actually one on e-bay right now and it's identical to mine. Thanks for all lthe help guys. Randy