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dual master cylinder


zephyrdave
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I'm in the process of converting my 41 Zephyr to a dual master cylinder.  I am using one from Speedway Motors..., and not the Mustang.  You need remote reservoirs as the MC is under the floor of the vehicle to fill it.  I am changing out the brake lines with stainless steel prefabbed ones from Classic Tubing.  All other brake components such as wheel cylinders need to be replaced too.  I am going to be using a vacuum assist on the master cylinder (7inch) unit to make the brakes work better.  Once it's all together it should be fine.  You should change the King Pins if any wear as well as steering linkage parts since you've gone that far.  Takes some efforts, but well worth it for a much better/safer braking system in today's worst traffic on the planet!

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A couple of items to ponder.  Can you fit the 7” booster under the floor without lowering the m/c.  You will need a vacuum port for the booster.  Hard to find without messing with the top of engine.  You only have a small hole in floor boards for the old ‘fruit jar m/c.  That will have to be addressed unless you go with remote  reservoirs.   

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Just now, Beltfed said:

A couple of items to ponder.  Can you fit the 7” booster under the floor without lowering the m/c.  You will need a vacuum port for the booster.  Hard to find without messing with the top of engine.  You only have a small hole in floor boards for the old ‘fruit jar m/c.  That will have to be addressed unless you go with remote  reservoirs.   Also remember, the smaller the bore on the m/c the higher the pressure output

 

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There is room under the floor for the booster to mount to the MC.  As to the vacuum line, it can run under the floor/firewall up to the manifold to connect.  Someone a while back posted a lot of photos of their conversion  process.  We can look for them so that it might help with the installation.  The main reason I am working on it is the safety aspect of the single MC brake system.  If you somehow loose brake pressure, the only thing you have is to gear it down and hope the emergency brake works.  With a dual MC you do have at least 2 other wheels to stop you.  With the remote reservoirs it's easy to keep the fluid topped off.  I will be using proportioning valves also to even out the braking from front to rear, with front taking a little more of the braking efforts.  

 

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Thanks for advice guys. My car has been on the road for 4 years after I restored it. I am considering the dual master for safety. The car stops pretty well now. No real issues, just thinking of safety. The mustang has 1" bore and I think my 39 might be 1 1/16. Not sure, can't remember.

DSC04941.JPG

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Definitely I would recommend replacing the MC with a dual.  And use proportional valves to balance front to rear stopping pressures.  You will need to install remote reservoirs under the hood to keep the MC filled as you won't be able to fill it under the floor as the old one did.  Speedway and Summit racing have parts to fix this.  I'm going to install a Wilwood dual cylinder with remote reservoirs and a 7 inch vacuum assist for much better braking.  Those reservoirs can be mounted with a kit under the hood so you can keep 'em full of brake fluid.  Speedway can help you with the setup.  

 

 

 

 

 

 

 

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I did the 7" dual booster and new master cylinder on my 48.  Had to make an adapter plate between booster and frame with a couple coupling nuts and a piece of 1/4 rod to use the stock pedals.  I mounted a new fill reservoir on inner fender.  You might want to consider the Speedway disk brake kit as well.  Uses Ford pickup disks and GM pistons.  My intake manifold had a tapped hole for vacuum to run windshield wipers, just put in a "T" and ran hose to booster. 

Abe

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  • 3 weeks later...

Just for information, I have driven my 1940 Mercury over 80,000 with the original type master cylinder since 1976, without a catastrophic failure. The system has had a couple of master cylinder failures and one wheel cylinder failure. 

 

The one master cylinder and the wheel cylinder failures were noticed when the pedal was lower than normal and the brake fluid level was low. I was still able to come to safe stops. The master cylinder leak started to show up when I was more than 90 miles from home and I made it home with some pedal left. If I had felt that the brakes would fail before I got home, I would have added fluid to the master cylinder before starting for home. The wheel cylinder problem was noticed when I was washing the car and saw the brake fluid on the tire.

 

The other master cylinder failure showed up as the pedal would get mushy in traffic, but return to normal after resting. I just replaced it and all of the hoses this spring.

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