I have heard the argument many times, claiming a properly maintained 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 composed 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 purist’s point of view, and although I strongly advocate for converting cars to 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.
What bore size master cyl. do you recommend for a 67 Mustang with 4 wheel Aerospace Disc?
Hello Gary,
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about 5 years ago I put radials on my 1951 Chevy pickup and converted to a dual master on 4 drums, two years ago I converted to a disk/drum set up and changed the master cylinder. the safety and, ride, handling and braking power improved greatly and I will never go back to bias ply tires and a 4 wheel drum set up. My wife just bought a 1951 Willys pickup, I have already ordered the front disk kit and dual master. Unless you don’t drive your classic much and keep the braking system impeccable, retaining a single master and 4 drums is just not safe.
I had an interesting experience on my 2002 Dakota. The two lines from the master cylinder were rubbing together after the plastic spacer must have succumbed to age and fallen off. The lines both burst at the same time. Fortunately I was on my property and in 4 wheel drive low, but still on a steep hill. The low gearing made it possible for me to have control and stop. I have a 1948 Chevy two ton that I was thinking of converting to dual, but decided not to. Getting the dual to work properly with the original linkage and balancing the pressure may have been more hazardous than the single system.
paul many moons ago i converted a 50 gmc to dual reservoir master cylinder. i used the original brake pedal and put the master cylinder and booster under the floor. since i worked in a machine shop i was able to make a linkeage that worked. reason for doing that was that i converted it to 4wd.
I’ve driven a Lot of older cars (In rough condition) even just to get them home or to a friends place to work on—
Having driven a lot of older cars (in rough shape) I’ve experienced brake failure–Total failure in single reservoir systems (Scary) (I’ve even crashed) But with a dual system I’ve always maintained control–Redundancy is a good thing–
I have a 1959 Edsel Corsair with drum/drum and the Treadlevac booster. Is there a conversion kit for my car? I also have a 1966 Plymouth Satellite that I would like to convert also. Is there a kit for that car? It is also drum/drum. Thanks!
Hello Kurt. Often the only solution for Tredelvac cars is to pull the entire system out of the car and replace it with a newer style booster and dual master cylinder.
You might want to check with the folks at Leed Brakes too, as they sometimes have solutions for difficult to fit cars. Here’s a link: https://leedbrakes.com/
The 1966 Satellite is a lot easier… in 1967 they switched to dual reservoir brakes and those parts will fit your car and are still available from sources like Rock Auto for under $50 for a master.
Mark
Classic Car Restoration Club
Owned 3 pre-1967 corvettes… each once, the first upgrade was to update to a 1967 dual MC. I learned the hard way in my high school car, a 1965 Impala Convertible. The brake line split in traffic and it was terrifying. Getting home was no joy either (backroads & emergency brake). Every old car since then, you guessed it. If you have a judged trailer queen – fine, get your show points, otherwise, it should be considered a mandatory upgrade to protect the car and yourself (in that order!)
I changed my single to dual on my 65 Impala with original drum brakes 👍
I have a 1932 Chevrolet Confederate, 2 door convertible coupe, old school HotRod. It has front disc, rear drum and a dual Master cylinder, The MC is mounted to the frame under the body, with no power booster. The brakes work fine but the pedal is kinda hard. Harder than other OE equipped manual brake cars that I have driven over the years. The firewall is clean for the no hood/hotrod look. All components are hidden. The MC has barely enough room to take the cap off and no service/inspection cover in the floorboard. No way to install the large drum style booster. How can I add an electric booster? Would I need a different MCyl because I see no fitting to accept a vaccum line? Do they mount to the MC or remote? Would adding an electric booster dramatically decrease my hard pedal? I want to keep the “Hidden look” and mount everything under the car. Like I said, The brakes work OK but the pedal is a little harder than I prefer. Also there is No parking/emergency brake at all. What are your suggestions? I enjoy and learn from your articles. Thanks. R.S.
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been doing this for many years. lost brakes on a single sys once the emer brake is almost no good. so a dual sys is the way to go. like to keep thing org but stoping is nicer. jim
1957 Thunderbird with drum/drum brakes. Thinking of going to power brake system, and am reading conflicting remarks as to the need for a proportioning valve in the system. Needed or not?
Hello Bobby. For safety reasons, adding power brakes is a great choice and so is converting to dual reservoir master cylinders.
The proportioning valve ONLY operates when rapid or panic stopping a car.
…and when the brakes are slowly applied it has no effect.
When panic stopping it reduces the flow of brake fluid to the rear brakes to prevent them from locking up first and putting the car into a skid.
In single reservoir systems often there was only a splitter that would split the brake fluid to both front and back lines.
In a dual reservoir system the front and back are separate systems and the prop valve serves to help maintain control of the vehicle in panic stop situations.
This is especially important when there’s reduced traction like a wet or icy road surface when the effects of locking up the rear brake first are more likely to send the car into an uncontrolled skid.
I prefer an adjustable proportioning valve for conversion applications, and factory preset prop valves for cars that were originally equipped with them.
Mark
Classic Car Restoration Club
This is very I just changed my 1952 Chevy styline Deluxe to a dual System from the stupid one that was underneath the floor which always leak
Brakes are the most important thing on a car. If a car stumbles or even quits; in all but the most unusual situations, you’ll be ok. If the brakes fail while driving, the opposite occurs- you’re more likely to be in an accident. That car you’ve restored likely doesn’t have all of the safety features built in which means you’re more likely to be injured and your car will be wrecked. Safety trumps everything.
I am restoring a ’66 Toronado which unfortunately has 4 drums instead of the front discs they switch to on the ’67’s. But I am putting on a dual reservoir system and removing the single for safety reasons. I have read different things regarding the use of a proportioning valve, whether it really is necessary or not. My conversion kit did come with one but I am wondering if it really is necessary? Thank you for any advice you can give!
Hello Roger. If you have one, I would install it.
The proportioning valve ONLY operates when rapid or panic stopping a car.
…and when the brakes are slowly applied it has no effect.
When panic stopping it reduces the flow of brake fluid to the rear brakes to prevent them from locking up first and putting the car into a skid.
In single reservoir systems often there was only a splitter that would split the brake fluid to both front and back lines.
In a dual reservoir system the front and back are separate systems and the prop valve serves to help maintain control of the vehicle in panic stop situations.
This is especially important when there’s reduced traction like a wet or icy road surface when the effects of locking up the rear brake first are more likely to send the car into an uncontrolled skid.
I prefer an adjustable proportioning valve for conversion applications, and factory preset prop valves for cars that were originally equipped with them.
Mark
Classic Car Restoration Club
I have a stock 1937 Buick Century and would like to change to a dual master cylinder. What product would be available to do this ?
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1937 buick century want to change single master cylinder to double
I whole heartedly agree with everything in this article, single master thinking is back with the guys that opposed four wheel brakes obselete
I absolutely agree about this I am English and on one particular occasion I was driving 70 M.P.H. legally on the A40 coming out of London and a heavily travelled roundabout was ahead I started slowing down but my brakes failed the pedal almost went to the floor I managed to stop the back drums are not that good but good enough if it hadn’t been for the dual master cylinder I would not be here now as I said the roundabout was full of cars and to have hit them at 70 or even 60 or 50 would have been fatal this was 1971 and I was driving a Cortina
Downshift & e-brake. Must be prepared if you’re going to drive classics.
trying to convert 56 bel air 6 cyl all drums to dual master cylinder. I haven’t found one that clears the oil filter canister. do they make a master cylinder that is narrow to provide the necessary clearance. thanks
Hi Al.
It’s been awhile since I last worked on a 6-cylinder Tri-Five. But as I recall the oil filter hangs off the intake manifold and in order to put on a dual master or larger power brakes, we simply unbolted the oil filter then re-attached it ahead of the carburetor,
Sometimes we needed longer lines… but not always. Also some models had brackets that lowered the mounting location, if you have room maybe a solution like that would work too.
Thanks
Mark-Classic Car Restoration Club
<strong What dual master cylinder will bolt up to a 1962 Pontiac Bonneville with power brakes and 4 wheel drum brakes
Hi Dennis,
Thanks for your patience, here is the answer:
The original factory booster will work, but it is a much better installation if you replace both the master and the booster at the same time as the ’62 booster uses a unique push rod.
I would suggest a Master Power Brakes (www.mpbrakes.com) Master/Booster unit designed for your car ( #BM17015-4 ).
Wrench Safe, Mark
Classic Car Restoration Club
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?
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
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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 . . . ?
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.
IT’S “BRAKES”…N-O-T ‘Breaks’ 😛
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?
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
I have a 67 international scout 800 with a single reservoir master cylinder. Is it hard to change it over to a dual ?
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
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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.
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).
Those that were born in the 80’s thru today are more likely into playing on computers. Those born a two or three decades earlier where more into cars. Perhaps part of that is the technology was different and vehicles had less technology involved.
thanks for the explanation. all of my douts are cleared.
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.
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.
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.
Great article and explanation! These are great tidbits that can teach everyone. Keep them coming!
Dave
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.
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
Hello, I just got a 1964 Dodge D700 and it has a one line,brake master cylinder and i would like to upgrade the brakes, but have not found much information on this problem. This system also has a large vacuum operated one line booster.
Any help would be appreciated.
Thank you and have a great day.
Loyce
Hi Loyce,
Thank you for your patience while I asked the experts, here is the reply:
Your D700 is a BIG truck! and a dual master conversion seems like a good idea.
Although we are not aware of anyone making a conversion kit for this truck as not too many are even restored.
The 1-1/2″ bore indicates you need to push a lot of volume and a booster is a must.
We would look at newer Big trucks in salvage yards to find a newer master/booster/pedal that will work with this truck.
Keep in mind the 1-1/2″ bore and measure the stroke to make certain your new system has the necessary amount of fluid movement.
Wrench Safe,
Mark
Classic Car Restoration Club
You should be able to find someone with a late 70’s early 80’s truck with the same GVW you could get everything off of ,not so much to use but to trade in the MC and booster for remans and get the lines for a pattern.
Mark, I have a 1928 Ford Model A with a 283 V-8. I am having issues with my brakes locking up after I drive it for a few hours. I am told that the master cylinder is too close to the headers. What would my solution be to fix this issue if you recommend not moving the master cylinder to the firewall? Thanks.
Hello Tim,
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