Dual chamber Master Cylinder conversion

[msstring]

I've seen some posts on here about conversion from the original single chamber to dual. I would love to do this for safety reasons if it can be done as a direct replacement. I have a '50 F3 with no vacuum boost. Any suggestions?

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[JSeery]

It can be done (for safety) but you have to be sure the pedal has enough stroke to take advantage of it. It is difficult to get 1/2 of the master cylinder to work because of the pedal arrangement in this old Fords.

[WABOOM]

I would love to add a dual MC to my 51 Mercury. I'll be watching this thread.
Look at this item I found on Ebay.
https://rover.ebay.com/rover/0/0/0?m...2F171026600991
It relocates the master cylinder assembly further back under the cab with this bracket to utilize the stock brake pedal lever. How difficult is it to upgrade to PB on a flathead? Can a flathead provide enough vacuum?

[Tinker]

oops... ugh my bad.

[Flathead Fever]

I worked on a fleet of 400 vehicles, a lot of those vehicles still had single master cylinders. Not once did I ever see a "single" brake system completely fail. With the exception of when a snow chain cross-link broke and sheared the metal brake line right off the wheel cylinders. That happened several times. That was the drivers fault for letting the cross-links wear too thin. We had bags and bags of new cross-links. All they had to do was ask and I would crimp-on new set of cross-links for them.

Back then, those phone company vehicles were being serviced every three-months. Part of that inspection was to put them up on a hoist and pull the drums and inspect the brakes. We pulled back the rubber dust boots on the wheel cylinders to see if they were beginning to leak. If we saw a little moisture we ignored it. If there was actual liquid behind the boot we rebuilt the cylinder and the one on the opposite side. We had an plastic box assortment of wheel cylinder cup sizes. We ran a ball hone through the cylinders. Wiped the bore clean with brake fluid and a paper towel until nothing showed up on the white paper. We replaced just the cups unless the outer boots were cracked then we used a kit with the piston, cups and the boots. A kit was half the price of a new wheel cylinder and just replacing the cups was probably less than a dollar a wheel cylinder. A lot of time you could leave the wheel cylinder on the vehicle and still run a hone through them. That way you did not need to disturb the metal brake line. On the mountain trucks the nuts on the brake lines would rust to the tubing and the tubing would twist with the nut. On those it was better not to mess with them so you didn't end-up making new metal lines. We rebuilt the wheel cylinders for year's, until we got bought out and the new corporation decided it was too big of a liability. We still did it if it kept a vehicle in service. You just didn't write it in the record's. I never saw a wheel cylinder completely fail.

We looked at the back of the master cylinders on each service to see if they were beginning to leak. You would see fluid running down the inside of the firewall if it was leaking. If the master cylinder was bolted to a vacuum brake booster then you could not see the back of the master cylinder. On those you pulled the vacuum line on the booster and stuck a small piece of rubber tubing down in there to make sure there was no brake fluid in the bottom of the booster, from a leaking master cylinder. You use a rubber hose because something like a welding rod could poke a hole in the booster's rubber diaphragm. If something is going to fail in a single brake system its going to be the master cylinder. Not because a seal completely blew-out but because of neglect. You could have a slow leak and the reservoir could run out of fluid. If you check your fluid level and its low you need to look at the back of the master cylinder for leakage. If its not leaking there and has lost a lot of fluid from a wheel cylinder you will see brake fluid on the brake backing plate. It might even being running down the tire if the car has been sitting a long time. The other thing that can happen to a master cylinder is dirt can block the little ports that allow the fluid to flow from the reservoir to the piston. You will press on the pedal and you won't have any. You step on it again and you have a normal pedal. If your master cylinder looks like mud inside this might happen to you. This only ever happened to me once and it was on my first car, a '65 Mustang fastback that was twelve-year's old. So was the brake fluid.

We also checked the rubber brake lines for cracks. They usually outlast the vehicle. We did have a recall on some of larger C-50 Chevy trucks for the right brake hose failing. They used the same hose on the left and on the right so what think a minute, what could possibly cause just the right hose to fail? The battery box was mounted right above the hose and the acid would drip down onto the crimped-on metal end of the brake hose and it would rust away. Then the rubber hose would blow-off the fitting. That took years to happen. I never saw a brake hose fail in the 30-year's I was there.

I have no problem trusting a single brake system that I have inspected. They are perfectly safe if maintained properly. Unless something rips off a brake hose or a steel line the system will not completely fail. If something does hit a steel line it usually crushes it but it doesn't tear. The most important thing is you don't have a dashboard warning light to tell you that your low on brake fluid. You have to check it once in awhile. I always glance at my tires when I'm walking up to my vehicle to make sure they are not going flat. At the same time I look at the bottom of brake backing plates to make sure they are not wet. If its been a long time since I have driven the vehicle I check the brake fluid level and the pedal travel.

I went to a Bendix brake training class. The instructor said that if you flushed out your brake fluid every two-year's the hydraulic parts like the master cylinder and wheel cylinders would last forever. Its the moisture that gets in the fluid that does the damage. Brake fluid is hydroscopic. That means it absorbs water at about 2% a year. This is funny, word search does not recognize "hydroscopic" its trying to change it to "hydroponic" There must be more marijuana growers than brake mechanics. Even though your brake system is sealed it expands and contracts with temperature change. This can draw moisture in past the seals. The most neglected system on a vehicle is the most important, the hydraulic portion of the brakes. Nobody ever changes their brake fluid? If its brown that is rust in your fluid. It can only rust if there is water in your brake fluid. Once it starts rusting its impossible to stop it. You can put new fluid in and it will just turn brown again. If the fluid is black, that is the your rubber cups going deteriorating. Its a hint that you should rebuild all the cylinders.

At the very least, on your daily drivers change the fluid every time you do a brake job. Your antique cars should still have their fluid changed every two year's but that's probably not going to happen, even in my own garage.

Next item. Built into your drum brake, master cylinder, is a residual check valve. It allows the brake fluid to return to the reservoir when you release the brake pedal but then it closes off leaving just a little pressure still in the system. Its not enough pressure to keep the wheel cylinder pistons from returning but its enough to push out the lips on the rubber cups, in the wheel cylinders, against the cylinder's bore and create a seal. This helps prevent the wheel cylinders from leaking. If the vehicle sits for a longtime that pressure is going to bleed off. If you have cars you don't drive at least get in them and stomp on the brakes a few times every once and a while. That will put the pressure back on the wheel cylinder cups.

Keep your brake fluid clean. Check your fluid level often. Make sure when you do check it that when you put the lid back on the master cylinder that the gasket is in place. If its not, your fluid could slosh out of the reservoir. This happens! There is nothing wrong with a single brake system if its maintained properly. It will not completely fail, except in old black and white movies.

[Tinker]

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not to forget to mention, why the e-brake is important. Its the mechanical override. As cars get more dependent on electronics and gadgets, the more a nice mechanical cable seems okay.

[Rascal]

Very informative & thank you for sharing, I agree regarding the single system, always reliable, and yes maintenance & observation is the key on old classics,

[V8 Bob]

Originally Posted by Tinker

Believe 56-58 fords ran dual mc's without a booster. Mustang 3 bolts are popular, with a re plumb on older fords.

The first year Fords used dual masters was '67, mandated by law. And what Mustang master has 3 bolts?

[V8 Bob]

Originally Posted by msstring

I've seen some posts on here about conversion from the original single chamber to dual. I would love to do this for safety reasons if it can be done as a direct replacement. I have a '50 F3 with no vacuum boost. Any suggestions?
Sent from my LM-G710VM using Tapatalk

First thing is to know the bore size of your present master.

[51 MERC-CT]

Originally Posted by WABOOM

I would love to add a dual MC to my 51 Mercury. I'll be watching this thread.
Look at this item I found on Ebay.
https://rover.ebay.com/rover/0/0/0?m...2F171026600991
It relocates the master cylinder assembly further back under the cab with this bracket to utilize the stock brake pedal lever. How difficult is it to upgrade to PB on a flathead? Can a flathead provide enough vacuum?

This is my installation of the PB on my '51 Merc. with use of bracket kit and 7" booster.

1979 GM (24mm bore) remote fill master cylinder.
Difficulty depends on the person doing the installation.
There is adequate vacuum to make it work perfectly.

[msstring]

Originally Posted by V8 Bob

First thing is to know the bore size of your present master.

I hope to get it opened up today. This truck has sat for 30 years. At one point the pedal was completely stuck. The one time I pushed hard enough that it freed up but no break. So that is why I think the MS needs to be rebuilt or replaced. I'll see what I find when I get into it.

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[msstring]

Thanks for the feedback. I agree the single chamber system may be perfectly fine as long as I make sure the lines are good.

But, I am skeptical because I did have the lovely pleasure of having the break system completely fail twice in one day on a little 12 ton straight truck.
First time sitting at a stop light and all of a sudden the pedal went to the floor. Surprised me but not a big deal drove in low gear to a service station got the line replaced and on my way.
Second time fully loaded coming down the ramp off the interstate. Brake pedal went straight to the floor, rolling 60 MPH down hill with a stop sign at the bottom!!! Laid on the horn and rolled straight through and up the other side where it finally slowed down enough that I was able to downshift and get stopped. That will get the blood pumping in a 16 year old kid!!! Was able to reverse back down the on ramp drove in low gear to a service station got the line replaced and went on my way home. All in a day's work .

An experience I will never forget, that was nearly 40 years ago. Fortunately no one was hurt.

I do agree though that all could have been avoided with better maintenance. I don't remember which line broke first. The second we figured was because the line had been disturbed during the first replacement.

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[JSeery]

Again, just realize that the dual setup will NOT work in most installations. So you may be depending on a safety factor that is not really there!

[msstring]

Originally Posted by 51 MERC-CT

This is my installation of the PB on my '51 Merc. with use of bracket kit and 7" booster.

1979 GM (24mm bore) remote fill master cylinder.
Difficulty depends on the person doing the installation.
There is adequate vacuum to make it work perfectly.

Thanks for sharing. This looks like a fun project but probably more than I want to bite off. [emoji4]

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[1948F-1Pickup]

Originally Posted by Flathead Fever

I worked on a fleet of 400 vehicles, a lot of those vehicles still had single master cylinders. Not once did I ever see a "single" brake system completely fail. With the exception of when a snow chain cross-link broke and sheared the metal brake line right off the wheel cylinders. That happened several times. That was the drivers fault for letting the cross-links wear too thin. We had bags and bags of new cross-links. All they had to do was ask and I would crimp-on new set of cross-links for them.

Back then, those phone company vehicles were being serviced every three-months. Part of that inspection was to put them up on a hoist and pull the drums and inspect the brakes. We pulled back the rubber dust boots on the wheel cylinders to see if they were beginning to leak. If we saw a little moisture we ignored it. If there was actual liquid behind the boot we rebuilt the cylinder and the one on the opposite side. We had an plastic box assortment of wheel cylinder cup sizes. We ran a ball hone through the cylinders. Wiped the bore clean with brake fluid and a paper towel until nothing showed up on the white paper. We replaced just the cups unless the outer boots were cracked then we used a kit with the piston, cups and the boots. A kit was half the price of a new wheel cylinder and just replacing the cups was probably less than a dollar a wheel cylinder. A lot of time you could leave the wheel cylinder on the vehicle and still run a hone through them. That way you did not need to disturb the metal brake line. On the mountain trucks the nuts on the brake lines would rust to the tubing and the tubing would twist with the nut. On those it was better not to mess with them so you didn't end-up making new metal lines. We rebuilt the wheel cylinders for year's, until we got bought out and the new corporation decided it was too big of a liability. We still did it if it kept a vehicle in service. You just didn't write it in the record's. I never saw a wheel cylinder completely fail.

We looked at the back of the master cylinders on each service to see if they were beginning to leak. You would see fluid running down the inside of the firewall if it was leaking. If the master cylinder was bolted to a vacuum brake booster then you could not see the back of the master cylinder. On those you pulled the vacuum line on the booster and stuck a small piece of rubber tubing down in there to make sure there was no brake fluid in the bottom of the booster, from a leaking master cylinder. You use a rubber hose because something like a welding rod could poke a hole in the booster's rubber diaphragm. If something is going to fail in a single brake system its going to be the master cylinder. Not because a seal completely blew-out but because of neglect. You could have a slow leak and the reservoir could run out of fluid. If you check your fluid level and its low you need to look at the back of the master cylinder for leakage. If its not leaking there and has lost a lot of fluid from a wheel cylinder you will see brake fluid on the brake backing plate. It might even being running down the tire if the car has been sitting a long time. The other thing that can happen to a master cylinder is dirt can block the little ports that allow the fluid to flow from the reservoir to the piston. You will press on the pedal and you won't have any. You step on it again and you have a normal pedal. If your master cylinder looks like mud inside this might happen to you. This only ever happened to me once and it was on my first car, a '65 Mustang fastback that was twelve-year's old. So was the brake fluid.

We also checked the rubber brake lines for cracks. They usually outlast the vehicle. We did have a recall on some of larger C-50 Chevy trucks for the right brake hose failing. They used the same hose on the left and on the right so what think a minute, what could possibly cause just the right hose to fail? The battery box was mounted right above the hose and the acid would drip down onto the crimped-on metal end of the brake hose and it would rust away. Then the rubber hose would blow-off the fitting. That took years to happen. I never saw a brake hose fail in the 30-year's I was there.

I have no problem trusting a single brake system that I have inspected. They are perfectly safe if maintained properly. Unless something rips off a brake hose or a steel line the system will not completely fail. If something does hit a steel line it usually crushes it but it doesn't tear. The most important thing is you don't have a dashboard warning light to tell you that your low on brake fluid. You have to check it once in awhile. I always glance at my tires when I'm walking up to my vehicle to make sure they are not going flat. At the same time I look at the bottom of brake backing plates to make sure they are not wet. If its been a long time since I have driven the vehicle I check the brake fluid level and the pedal travel.

I went to a Bendix brake training class. The instructor said that if you flushed out your brake fluid every two-year's the hydraulic parts like the master cylinder and wheel cylinders would last forever. Its the moisture that gets in the fluid that does the damage. Brake fluid is hydroscopic. That means it absorbs water at about 2% a year. This is funny, word search does not recognize "hydroscopic" its trying to change it to "hydroponic" There must be more marijuana growers than brake mechanics. Even though your brake system is sealed it expands and contracts with temperature change. This can draw moisture in past the seals. The most neglected system on a vehicle is the most important, the hydraulic portion of the brakes. Nobody ever changes their brake fluid? If its brown that is rust in your fluid. It can only rust if there is water in your brake fluid. Once it starts rusting its impossible to stop it. You can put new fluid in and it will just turn brown again. If the fluid is black, that is the your rubber cups going deteriorating. Its a hint that you should rebuild all the cylinders.

At the very least, on your daily drivers change the fluid every time you do a brake job. Your antique cars should still have their fluid changed every two year's but that's probably not going to happen, even in my own garage.

Next item. Built into your drum brake, master cylinder, is a residual check valve. It allows the brake fluid to return to the reservoir when you release the brake pedal but then it closes off leaving just a little pressure still in the system. Its not enough pressure to keep the wheel cylinder pistons from returning but its enough to push out the lips on the rubber cups, in the wheel cylinders, against the cylinder's bore and create a seal. This helps prevent the wheel cylinders from leaking. If the vehicle sits for a longtime that pressure is going to bleed off. If you have cars you don't drive at least get in them and stomp on the brakes a few times every once and a while. That will put the pressure back on the wheel cylinder cups.

Keep your brake fluid clean. Check your fluid level often. Make sure when you do check it that when you put the lid back on the master cylinder that the gasket is in place. If its not, your fluid could slosh out of the reservoir. This happens! There is nothing wrong with a single brake system if its maintained properly. It will not completely fail, except in old black and white movies.

Lotta truth there.
More worried about the under-maintained brake systems in the real world, driven by today's drivers..... and maybe a bypassing master, not out and out failure. Pedal to the floor nowadays is probably all it would take for disaster with today's drivers, close following distance and higher speeds.

[V8 Bob]

Originally Posted by JSeery

Again, just realize that the dual setup will NOT work in most installations. So you may be depending on a safety factor that is not really there!

Simply NOT true. You may have issues with dual masters, but they do work in all installations when set up properly. Knowledge of their operation is key, something many still do not fully understand, even after 50 years! Discouraging proven safety related items is not in anybody's best interest.

[1948F-1Pickup]

Originally Posted by msstring

I've seen some posts on here about conversion from the original single chamber to dual. I would love to do this for safety reasons if it can be done as a direct replacement. I have a '50 F3 with no vacuum boost. Any suggestions?

Sent from my LM-G710VM using Tapatalk

Don't know about an F-3 (is it the same x-member where the master cylinder attaches?) but I have a 67/68 Mustang dual reservoir master on my F-1. It's a 1" bore. Works fine; maybe 1" longer pedal stroke with slightly
less uumph required. I think the original F-1 master was 1 1/16"
F-3 I think was 1 1/4" ? At 1 1/4" you'd be into quite a bit of additional brake pedal travel going down to a 1" master. You'd have to do some
research to come up with a bigger bore..... might be a bit of a trick coming
up with 1 1/4 because at that size you're normally dealing with power brake
master cylinders and a different pushrod situation.

I think mine is an EIS master but the 1" 67-70 Mustang manual Drum Drum is Wagner #F73323

A lot of companies offer a 2 bolt to 3 bolt conversion plate. I've got one from Engineered Components (EC-410A) on my F-1.

[JSeery]

Originally Posted by V8 Bob

Simply NOT true. You may have issues with dual masters, but they do work in all installations when set up properly. Knowledge of their operation is key, something many still do not fully understand, even after 50 years! Discouraging proven safety related items is not in anybody's best interest.

That was the point Bob, and it is true in most installations. It takes real effort and knowledge and without that a dual master cylinder offers no safety whatever. You need to understand how it works and what it takes to get it to work on a single circuit or it is no value whatever. This is not discouraging safety related items, it is pointing out that there is no safety at all unless it is installed in a manner that allows it to function, and that is often difficult in these cars. Encouraging someone to install something that will not work as they think it will is not a good plan IMO.

[40cpe]

You speak of "real effort and knowledge" needed to make the dual cylinder work correctly. Beside the correct bore of the cylinder, isn't the stroke of the pedal/actuating rod the critical factor here? From what I've read, the emergency braking occurs at the very bottom of the pedal stroke and if the pedal/rod geometry isn't correct there might not be enough stroke to activate the good side of the system if a failure occurs on one side. Is there a comprehensive article on things to check when converting to a dual MC?

[V8 Bob]

Originally Posted by 40cpe

You speak of "real effort and knowledge" needed to make the dual cylinder work correctly. Beside the correct bore of the cylinder, isn't the stroke of the pedal/actuating rod the critical factor here? From what I've read, the emergency braking occurs at the very bottom of the pedal stroke and if the pedal/rod geometry isn't correct there might not be enough stroke to activate the good side of the system if a failure occurs on one side. Is there a comprehensive article on things to check when converting to a dual MC?

The dual master cylinder has to be able to full stroke before the pedal bottoms out and this should be checked initially with a dry system.

When a system failure occurs, that system's piston in the master will stroke it's full distance, resulting in an increase of pedal travel, but allowing full brake pressure in the other circuit. This should be verified while bleeding; the primary or secondary circuit should be functional with the other system open.