Single vs. Dual Reservoir Master Cylinders

SINGLE VS. DUAL

I have heard the arguments many times, claiming a properly maintained and working single reservoir master cylinder is just as safe as a dual reservoir system. My response is always the same, “if a single reservoir system is so good, then why are they no longer offered?” Often when things go wrong with a car mechanically, there is no warning they are about to fail, and most long-time enthusiasts have had their share of new or rebuilt parts fail as well. Brake systems are comprised of numerous parts, all-working together to stop the vehicle. As cars evolved from four-wheel drum systems to disc/drum combinations, the design of the various components making up the system changed in order to keep pace with the new technology. One important change was the shift from single reservoir master cylinders to dual reservoir master cylinders.

Originally developed to handle the different fluid volume requirements for disc/drum brake combinations, it became quickly evident the dual reservoir systems also offered important safety benefits that were equally as applicable to the drum/drum brake cars as well. Single reservoir master cylinders provide pressure to both the front and rear systems, however, should a failure occur somewhere in the system, there is a very good chance that all brakes will be lost in the vehicle. With a dual reservoir system the brake circuits are split into front and rear, and in the event of a failure you have a much better chance of safely stopping the vehicle.

Typically in disc/drum dual reservoir master cylinders, one of the reservoirs is larger than the other. Often the larger reservoir is for the disc brakes although some models of cars exist where this is reversed. Many new cars today, have a single reservoir although the reservoir splits internally when the fluid drops to a lower level, these systems also still use separate front and back brake circuits.

When using a dual reservoir master with disc brakes on the front, the output pressure is equal on each port and must be regulated or adjusted through an external proportioning valve to provide proper balance.

I understand the purists point of view, and although I strongly advocate for converting cars to use dual reservoir master cylinders, at the very least any enthusiast running a single reservoir master cylinder, should ensure their emergency brake system is in top working order and test it often.

Discussion
  • (will not be published)

17 Responses to “Single vs. Dual Reservoir Master Cylinders”
  1. Merton Keith

    On many 1940’s & 1950’s cars and trucks the master cylinder and if used also the booster is mounted under the floorboard on the longitudinal frame rail. Also many of these vehicles other than Chevy’s there is no bolt in kit to convert. It’s all Jake leg modification, although I could do with lots of work, I don’t think good on brake systems. Also many modifications change the master cyl. to the firewall, sometimes the original defroster must be deleted also vehicle originality is lost. I don’t think whom ever wrote this article has a conception of what it takes to do a dual master cyl. change over.

    Reply
    • Mark Simpson

      No offense taken…
      Although I have converted numerous cars from single to dual reservoir.
      We agree that the Master cylinder should be placed exactly where the original was (or close), as I too don’t like to see them hanging off the firewall if they were never there in the fist place. Yes Most Ford’s and Chevy’s have kits available to make the job easier, but many of these same kits with minor modifications also fit Chryslers, Packards, Studebakers, etc…
      I agree you must feel confident in your own fabrication skills before altering brake system components. but in all the conversions I have done I have never run into a situation that made the conversion impossible.

      Wrench Safe, Mark

      Reply
  2. Dale

    I agree one hundred per cent on the change to a dual master system. When one spends a small fortune on performance and suspension upgrades, it seems that far to often , the braking is not even addressed other than a clean up and some new friction. The change up is pretty simple to complete, and is FAR SAFER than the use of a PARK BRAKE that has always fallen under the MISNOMER of an “emergency” brake.

    Reply
  3. Howard Scheetz

    Totally agree. I lost all fluid in an old single reservoir Dodge. Yes, my emergency system worked well. However, the dual systems increase the safety factor. I intend to switch my recently purchased ’52 to a dual system this winter.

    Reply
  4. n2oldcars

    This is classic car RESTORATION club isn`t? A dual master cylinder is great for regular use cars, restomods, hot rods ect…But for a true restoration,then the original braking systems needs to be used.I`ve gone both routes with good results.

    Reply
  5. Jim Morace

    You are 100% right on. I have a 1965 Mustang that I just changed over to a Dual system. My son is old enough to dive now and always asked to take the Mustang out, Now he can. Kid’s don’t know about a parking brake.

    Reply
    • Carter Gorman

      Reading the post above made me wonder: Are kids less intelligent now than they were in 1989? Or are the parents? When I was 16 in 1989 I was given my 1st car as a present from my folks. An inexpensive 1964 Ford Falcon 2-door Standard Series sedan. I drove it with its non-power brake system to school and everywhere else I needed to go. And my folks mentioned the parking brake, too. → Your son could have taken your ’65 Mustang out to drive with its single master cylinder braking system before you changed it over. It’s not as if you’re standing aloof and are out of the picture . . . you are ~right there~ to instruct him about what a parking brake is. “Kids don’t know about a parking brake” — well, they would if you’d tell them! My parents told me! It has never occurred to me that parking brakes were such a complex issue that are not easily explained between Parent and Child. Maybe I’ve missed something over the past 29 years? I do know old cars are ~still~ old. Anyway, I didn’t have a choice: I either had to drive the Falcon or continue riding to school every day in that godawful Palm Beach County bus. → I picked the Falcon — complete with single-master cylinder system (and parking brake).

      Reply
  6. Allan

    I have a 67 international scout 800 with a single reservoir master cylinder. Is it hard to change it over to a dual ?

    Reply
    • Customer Service

      Hello Allan,

      Switching from single reservoir master cylinders to dual, is one upgrade that is simply a must if you intend to drive your car/truck on a regular basis. if you are not making any disc brake conversions also the upgrade in most cases is very simple.

      Remove the old Master Cylinder, and line to the tee. There should be three lines leaving the tee, one to each front brake and one to the rear brakes. Disconnect the rear brake line from the tee, and insert the correct size flare nut plug into the tee where the rear line used to be. Now add a flare fitting splice to the end of the rear brake line. Install the new dual reservoir master cylinder, on your truck I believe the 1968 Scout used a dual reservoir master, and will bolt right up. You might want to check out the offerings from (www.ihpartsamerica.com). Now finish the connection by adding one line from the master to the tee, and another connecting the master to the rear brake line.

      Bleed the brakes and you’re done.

      Wrench Safe,
      Mark CCRC Video Membership

      We’d love to have you be a part of our community. We are convinced you will enjoy the benefits of becoming a member and having access to the best instructional how to videos and professional tips. We would like to offer you a special promotion for your first year membership.
      https://go.classiccarrestorationclub.com/C11291

      Reply
  7. Joe

    I installed a brake modification kit on my 63 Vette replacing the single master cylinder with a dual master cylinder. It seems to require more pedal pressure to stop than when it was a single master cylinder. Is this a common occurrence when switching to a dual system?

    Reply
    • Customer Service

      Hi Joe,

      Perhaps your new master cylinder has a bigger bore, which would require more stopping pressure to achieve the same braking force.

      The stock ’63 Corvette master has a 7/8-inch bore, if your new master is a common 1-inch bore it will take more foot pressure to achieve the same amount of brake pressure.

      Wrench Safe,

      Mark
      Classic Car Restoration Club Video Membership

      Reply
  8. Domenic

    I agree that dual masters is better. However, it is my understanding that with the advent of anti locking breaks it doesn’t seem to matter. I have a dual master cylinder on my 2004 Tahoe. One line broke coming out of the master cylinder and I lost all breaks in the truck. I was told it was because of the anti locking break system. Trust me, it was a huge surprise to me.

    Reply
  9. Carter Gorman

    The ’emergency braking system’ on my ’64 Ford Falcon is a handle underneath the steering wheel. Primitive even by 1964 standards, I reckon. I’ve never considered upgrading my single master cylinder braking system to a dual reservoir system. That said, I have the brakes checked every time I take the car in for servicing. I don’t want to go crashing into stuff, either! I figure the non-power brakes have worked as they are for 54 years now on a 2,500 pound car so I’m just going to leave them as they are. NOTE that I’m not saying a single master cylinder braking system is as good or safe as a dual master-cylinder reservoir braking system but as long as my brakes are working well with the yearly check-ups I’m not going to switch the system over. I don’t see myself as an automotive enthusiast or a purist in that I’m simply leaving the equipment alone that came with the car. If, when I became the owner of the Falcon in 1989, the braking system had already been ^upgraded^ to a dual reservoir master cylinder I’d have just left that alone, too. I can’t see any way I’d have had the brakes changed back original ‘single’ specs. A THOUGHT: Do cars with upgraded braking systems lose points for non-originality at the Concours d’Elegance? I wonder . . . ?

    Reply
  10. Todd Rauch

    I have a 1966 Ford F100. I want to update my braking system. Here my plan keep the drum brakes. Replace all of my brake shoes and brake line. The front brakes I want to covert to disc brakes with a a double master cylinder with a brake booster. Does this sound ok?

    Reply
    • Customer Service

      Hello Todd,

      Your planned upgrades are the same as most upgraded cars and trucks on the road, and should serve you well for years to come.
      Go for it you’ll be very happy you did.

      Thanks,

      Mark
      Classic Car Restoration Club Video Membership

      We’d love to have you be a part of our community. We are convinced you will enjoy the benefits of becoming a member and having access to the best instructional how to videos and professional tips. We would like to offer you a special promotion for your first year membership.
      https://go.ClassicCarRestorationClub.com/C14156

      Reply